Front. Microbiol. Frontiers in Microbiology Front. Microbiol. 1664-302X Frontiers Media S.A. 10.3389/fmicb.2025.1741549 Original Research Postbiotic metabolites present in the supernatants of Lysinibacillus xylanilyticus and Bacillus cereus promote the germination and growth of Hibiscus sabdariffa and Prosopis juliflora Ruiz-Aymá Gabriel 1 † Investigation Resources Writing – original draft Formal analysis Data curation Writing – review & editing Romero-Arguelles Ricardo 1 † Writing – review & editing Data curation Conceptualization Writing – original draft Rios-Del Toro Esther E. 1 Project administration Visualization Writing – review & editing Formal analysis Methodology Writing – original draft Funding acquisition Juarez-Gaspar Alexa 1 Writing – review & editing Methodology Writing – original draft Visualization Supervision Olalla-Kerstupp Alina 1 Software Writing – original draft Formal analysis Writing – review & editing Loredo-Tovias Marco 2 Writing – review & editing Methodology Resources Conceptualization Visualization Writing – original draft González-Rojas José I. 1 Supervision Writing – review & editing Resources Writing – original draft Villarreal-Treviño Licet 3 Resources Writing – review & editing Supervision Investigation Writing – original draft Guzmán-Velasco Antonio 1 * Data curation Validation Resources Visualization Methodology Conceptualization Project administration Formal analysis Investigation Writing – review & editing Funding acquisition Supervision Software Writing – original draft Gomez-Govea Mayra A. 1 * Writing – review & editing Funding acquisition Resources Writing – original draft Investigation Project administration Data curation Software Visualization Universidad Autónoma de Nuevo León, Facultad de Ciencias Biológicas, Laboratorio de Biológia de la Conservacion y Desarrollo Sostenible, San Nicolás de los Garza, Mexico Universidad Autonoma de San Luis Potosi, Facultad de Ingenieria, Laboratorio de Agua y Suelo, San Luis Potosi, Mexico Universidad Autónoma de Nuevo León, Facultad de Ciencias Biológicas, Laboratorio de Microbiología General, San Nicolás de los Garza, Mexico Correspondence: Mayra A. Gomez-Govea, mayra.gomezgv@uanl.edu.mx Antonio Guzmán-Velasco, antonio.guzman@uanl.mx

These authors have contributed equally to this work and share first authorship

 23 01 2026 2025 16 1741549 07 11 2025 16 12 2025 26 12 2025 Copyright © 2026 Ruiz-Aymá, Romero-Arguelles, Ríos-Del Toro, Juarez-Gaspar, Olalla-Kerstupp, Loredo-Tovias, González-Rojas, Villarreal-Treviño, Guzmán-Velasco and Gomez-Govea. 2026 Ruiz-Aymá, Romero-Arguelles, Ríos-Del Toro, Juarez-Gaspar, Olalla-Kerstupp, Loredo-Tovias, González-Rojas, Villarreal-Treviño, Guzmán-Velasco and Gomez-Govea https://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Introduction

The search for sustainable agricultural strategies has highlighted the importance of plant-microbe interactions within soil ecosystems. In particular, extracellular metabolites produced by soil bacteria represent a promising, yet underexplored, source of bioactive compounds capable of modulating plant germination and early development.

 Methods

This study evaluated the biostimulant potential of extracellular metabolites present in bacterial cell-free supernatants on the germination and early growth of Hibiscus sabdariffa and Prosopis juliflora under controlled laboratory conditions. Two native bacterial strains isolated from soils of Nuevo León, Mexico, were identified as Lysinibacillus xylanilyticus and Bacillus cereus using MALDI-TOF mass spectrometry. Supernatants obtained after cultivation in Luria–Bertani (LB) medium were applied directly to seeds, and germination and growth parameters were recorded. Phytochemical screening of the supernatants was also performed.

 Results

The L. xylanilyticus supernatant significantly enhanced seed germination (96.66 ± 5.77%; p < 0.0001) and promoted early growth in both plant species, increasing shoot length, leaf width, and fresh biomass. In contrast, the B. cereus supernatant inhibited H. sabdariffa germination (30 ± 10%; p = 0.0146) and showed limited effects on P. juliflora. Notably, a 50:50 mixture of both supernatants completely inhibited H. sabdariffa germination while significantly stimulating P. juliflora germination (90 ± 10%; p = 0.0130). Phytochemical analysis revealed low concentrations of carbohydrates and coumarins, suggesting that the observed effects were likely mediated by other, unidentified bioactive metabolites.

 Discussion

These findings demonstrate that extracellular metabolites produced by soil-derived bacteria exert species-specific and measurable biological effects on seed germination and early plant growth. The contrasting responses observed between plant species and supernatant combinations underscore the complexity of plant–microbe chemical interactions. Overall, this study highlights the potential of bacterial extracellular metabolites as microbiome-based tools for sustainable agriculture and ecological restoration.

 bacteria bio-stimulants germination posbiotic supernatants The author(s) declared that financial support was received for this work and/or its publication. This work was funded by the Secretaría de Ciencia, Humanidades, Tecnología e Innovación (SECIHTI) grant no. CBF2023-2024-2946. In addition to financial support through SNI-Level 1 (MG-G), SNI-Level 1 (GR-A), SNI-Level candidate (RR-A), SNI-Level 1 (ET), SNI-Level 1 (AO-K), SNI-Level 1 (JG-R), SNI-Level 2 (LV-T), and SNI-Level 1 (AG-V). section-at-acceptance Microbe and Virus Interactions with Plants Introduction

Agriculture continues to be a fundamental pillar of global sustainability, particularly considering the sustained increase in food demand resulting from rapid population growth (Liakos et al., 2018). In this context, the transition to sustainable agricultural systems has driven the search for strategies that reduce the environmental impact of conventional practices (Keswani et al., 2020). Currently, agricultural productivity depends largely on the intensive use of inorganic chemical fertilizers, whose prolonged use poses serious ecological risks, including soil degradation, aquifer contamination, and disruption of native microbial communities (Bhardwaj et al., 2014). Soil microbial communities play an essential role in the fertility and functionality of agricultural ecosystems thanks to their wide metabolic diversity, which can directly influence plant nutrition and development (Keswani et al., 2020). This knowledge has driven the development of biofertilizers, biological products that promote plant growth through mechanisms such as biological nitrogen fixation, phosphate solubilization, or phytohormone synthesis, constituting an ecological and sustainable alternative to synthetic fertilizers (Vasseur-Coronado et al., 2021). Numerous studies have documented the positive effect of plant growth-promoting rhizobacteria (PGPR) and mycorrhizal fungi on nutrient availability and crop productivity (Canbolat et al., 2006; Arango et al., 2011; Hakim et al., 2021; Zuluaga et al., 2021; Homthong et al., 2022; Maia et al., 2023). However, the effectiveness of these biotechnologies may be limited by the low persistence of inoculated microorganisms in the soil and their possible interactions with native microbial communities, factors that determine the success of inoculation (Manfredini et al., 2021). Within this framework, bioactive compounds discharged by soil microorganisms, including secondary metabolites and extracellular enzymes, are increasingly recognized as crucial in regulating plant growth and shaping the functional dynamics of the rhizosphere (Pandey et al., 2020). Recently, there has been increased interest in so-called postbiotics, defined as preparations containing inactivated (non-viable) microorganisms and/or their biologically active metabolites, capable of inducing beneficial effects in plants or soil without relying on active microbial colonization (Hijová, 2024). This approach represents a promising and more controllable strategy compared to traditional biofertilizers.

Postbiotic metabolites comprise a wide range of molecules with diverse ecological and physiological functions, including organic acids (acetic, lactic), bacterial phytohormones such as indole-3-acetic acid (IAA) and gibberellins, antimicrobial lipopeptides (surfactin, fengicin, iturin), siderophores, and volatile organic compounds (VOCs), among others (Olanrewaju et al., 2017). Among the most relevant secondary metabolites are bacteriocins and antimicrobial peptides, widely described in genera such as Pseudomonas, Bacillus, Streptomyces, and Stenotrophomonas, characterized by their ability to produce antibiotics and antifungal compounds (Compant et al., 2005; Sansinenea and Ortiz, 2011). Likewise, species of Serratia, Paenibacillus, and Pseudomonas synthesize extracellular enzymes such as chitinase, which play a crucial role in the biological control of phytopathogens (Ordentlich et al., 1988; Lim et al., 1991). More than 90% of soil bacteria produce siderophores, low molecular weight molecules that chelate ferric iron (Fe3+) from the environment, increasing its bioavailability to plants (Sayyed et al., 2013). The most prominent genera include Enterobacter, Rhodococcus, Bacillus, and Pseudomonas (Shah et al., 2022). In addition, various soil bacteria synthesize phytohormones such as IAA, cytokinins, gibberellins, and abscisic acid, which act as natural biostimulants of plant development (Xu et al., 2023; Poveda and González-Andrés, 2021). These postbiotic molecules represent sustainable alternatives with low environmental impact that can contribute to improving nutrient availability, suppressing diseases, and stimulating plant growth, promoting more resilient and ecologically balanced agriculture (Hijová, 2024).

In this context, the selection of bacterial strains and model plant species is crucial for evaluating the potential application of postbiotics. L. xylanilyticus and B. cereus are soil bacteria widely distributed in arid and semi-arid ecosystems, recognized for their ability to produce extracellular enzymes, siderophores, and phytohormones. Both were isolated from native soils in Nuevo León, Mexico, making them representative of local conditions and of interest for use in bio-stimulation strategies adapted to water-limited environments. The selected plants, H. sabdariffa and P. juliflora, are contrasting but complementary models within the framework of regional sustainable agriculture. H. sabdariffa is a crop of high agronomic and commercial value, traditionally grown under low-tech conditions, while P. juliflora is a xerophytic species widely distributed in semi-arid areas, recognized both for its forage utility and for its invasive nature and adaptability to degraded soils. The comparative study of both species allows for the evaluation of the physiological response to postbiotics in plants with divergent ecological strategies: one of productive interest (H. sabdariffa) and the other of ecological relevance (P. juliflora). Therefore, the objective of this study was to evaluate the effects of postbiotic metabolites present in supernatants produced during the growth of L. xylanilyticus and B. cereus on the germination and development of H. sabdariffa and P. juliflora, to explore their potential as bio-stimulants or biological control agents in different agricultural contexts.

 Materials and methods Strains

The strains of L. xylanilyticus and B. cereus were isolated from soil samples collected in the town of Iturbide, Nuevo León, Mexico, located in the Sierra Madre Oriental, at an altitude between 1,250 and 2,258 m above sea level (coordinates: 24°45′24.6′′ N 99°53′35.5′′ W). The strains were identified using an automated MALDI-TOF mass spectrometry system (BD™ Bruker MALDI Biotyper™). The mother cultures were stored at −80 °C in Luria-Bertani (LB) broth (Difco, Mexico) supplemented with 20% glycerol (Sigma-Aldrich, Mexico). Fresh cultures were obtained by inoculating an aliquot into 5 ml of LB broth and incubating overnight (18–20 h) at 37 °C.

 Postbiotic production

L. xylanilyticus and B. cereus were cultured in 1,000 m of Luria-Bertani (LB) broth at a concentration of 1 × 106 cells/ml at 37 °C with constant agitation (150 rpm). McFarland standards were used to count the inoculum. When the cultures reached the end of the logarithmic growth phase (12 h), they were centrifuged (Thermo Scientific Sorvall Lynx 6000) at 13,000 × g for 15 min at 4 ± 2 °C to separate the cell pellets from the supernatants. Once centrifuged, the supernatants were filtered with a 0.22 μm filter to prevent live bacterial cells from interfering with the experiments. An incubation time of 12 h was selected based on the growth curves of the two bacterial strains (Supplementary Figure 1) and previous reports indicating that the production of metabolites with relevant biological activities occurs predominantly in the late logarithmic and early stationary phases (Gómez-Govea et al., 2017). Finally, the supernatants were stored in sterile glass bottles at −80 °C until use.

 Bioassays

Bioassays were conducted to evaluate the effects of postbiotics present in the supernatants of L. xylanilyticus and B. cereus on seed germination and plant growth. The following treatments were selected for this purpose: supernatants of L. xylanilyticus, supernatants of B. cereus, and a combination of both supernatants in a 50:50 ratio. Distilled water and sterile LB broth were used as controls. Each bioassay consisted of five independent replicates, with ten seeds per treatment.

 Effects of <italic>L. xylanilyticus</italic> and <italic>B. cereus</italic> supernatants on the germination of <italic>Hibiscus sabdariffa</italic> and <italic>Prosopis juliflora</italic> under laboratory conditions

The supernatants were applied to the seeds following the methodology described by Smyth et al. (2011), with minor modifications. In summary, ten seeds per treatment were placed on sterile filter paper inside plastic containers disinfected with 70% ethanol. The treatments were applied using sterile sprayers (1.4 ml initial application), followed by misting with distilled water twice a day for seven consecutive days under aseptic conditions. Germination tests were performed in the dark at 25 ± 2 °C. A seed was considered to have germinated when the radicle reached at least 1 cm in length. The germination percentage (GP) was calculated according to ISTA (2015) as the ratio of the total number of germinated seeds to the total number of seeds sown, multiplied by 100. The germination rate was evaluated using the germination rate index (GRI) described by Maguire (1962), calculated using formula (Maguire, 1962):

I⁢V⁢G=∑GiTi

Where Gi is the number of seeds germinated on the i day, and Ti is the number of days from sowing to that observation. This method accounts for both the number of seeds germinated and the time required for germination, providing an estimate of seedling emergence vigor.

 Effect of <italic>Hibiscus sabdariffa</italic> and <italic>Prosopis juliflora</italic> growth with <italic>L. xylanilyticus</italic> and <italic>B. cereus</italic> supernatants

For this test, the seeds of both plants were germinated with distilled water under the conditions described above. Once the seeds had germinated, the supernatants were evaluated for plant growth using the methods described by Van Staden et al. (2020) and Santiago et al. (2020), with minor modifications. The seedlings were transplanted into sterile soil collected from the site where the bacterial strains were isolated, in 15 cm × 15 cm black polyethylene bags containing 100 g of soil. These were kept in greenhouse conditions with a controlled temperature of 25 ± 2 °C and a photoperiod of 18:6 (light:darkness). The variables evaluated were stem diameter, leaf width, leaf length, and fresh weight. At the time of transplanting (time = 0), 15 ml of each treatment was applied directly to the soil: supernatant of L. xylanilyticus, supernatant of B. cereus, and a 50:50 mixture of both supernatants, including the controls. Seven days after transplanting, the treatments were reapplied (15 ml per pot). After this, the plants were watered once a day with 15 ml of tap water for four weeks. Each bioassay consisted of five independent replicates, with ten seeds per treatment.

 Phytochemical analysis of supernatants

Preliminary identification of secondary metabolites in plant extracts was carried out by qualitative phytochemical screening tests (Romero-Arguelles et al., 2025). For the detection of alkaloids, the Dragendorff test was used, in which 1 mg of the extract was dissolved in 2 mL of methanol and four drops of the reagent previously prepared from two solutions were added: one with Bi(NO3)3 in acetic acid and water (Solution A), and the other with potassium iodide (Solution B); the formation of a persistent red–orange coloration indicated a positive result. Carbohydrates were identified by Molisch’s test, adding the corresponding reagent and concentrated sulfuric acid, and were considered positive if a purple ring formed at the interface. To detect coumarins, 10% sodium hydroxide was used on the extract dissolved in methanol, observing a yellow coloration that disappeared upon acidification. The instaurations were determined with 2% potassium permanganate, evidencing a positive test by discoloration or brown precipitate of MnO2. Flavonoids were detected with concentrated sulfuric acid, differentiating subtypes by the color changes observed. For quinones, the extract, ethanol, and 5% NaOH were mixed, and the color formation and its UV spectrum were recorded. Saponins were identified with concentrated H2SO4 and 10% NaHCO3, being considered positive due to the formation of persistent bubbles. Sesquiterpene lactones were detected by the Baljet test, using a mixture of picric acid and NaOH, which resulted in a change from orange to dark red. Sterols and terpenes were evaluated by the Salkowski test, adding sulfuric acid to a chloroform solution of the extract, with a red–brown ring as a positive indication. Finally, phenolic compounds (tannins) were detected with 2.5% FeCl3, generating red, blue–violet, or green precipitates as a positive reaction.

 Statistical analysis

All quantitative measurements were performed using three independent biological replicates, and the results are expressed as mean ± standard deviation (SD). Prior to inferential analysis, data normality within each experimental group was assessed using the Shapiro–Wilk test, and homogeneity of variances was verified using Levene’s test. When the data met the assumptions of normality and homoscedasticity, comparisons among treatments were conducted using one-way analysis of variance (ANOVA), followed by Tukey’s post-hoc test for multiple comparisons. In cases where at least one assumption was not met (p < 0.05), nonparametric tests were applied, using the Kruskal–Wallis test for global comparisons among treatments. All statistical analyses were performed using GraphPad Prism version 9.0 (GraphPad Software Inc., San Diego, CA, USA). Values of p < 0.05 were considered statistically significant.

 Results Characterization of isolated bacterial strains

Two bacterial strains were isolated from the soil sample collected (B7 and B9). Once isolated, they were characterized using mass spectrophotometric analysis (MALDI-TOF), resulting in a relationship between strain B7 and Lysinibacillus xylanilyticus with a score of 2.00. On the other hand, the results of the identification of strain B9 showed a relationship with Bacillus cereus with a score of 2.19 (Table 1).

Identification of bacteria isolated from soil samples based on mass spectrometry.

Strain Identification Score
B7 Lysinibacillus xylanilyticus 2.00
B9 Bacillus cereus 2.19
Effects of <italic>Lysinibacillus xylanilyticus</italic> and <italic>Bacillus cereus</italic> supernatants on the germination of <italic>Hibiscus sabdariffa</italic> and <italic>Prosopis juliflora</italic> under laboratory conditions

The effect of cell-free supernatants from L. xylanilyticus and B. cereus was evaluated by applying them directly to seeds of H. sabdariffa and P. juliflora. The results showed that treatments based on L. xylanilyticus supernatant significantly promoted germination by 96.66 ± 5.77% (p < 0.0001) compared to the LB broth control, while B. cereus supernatant significantly reduced the germination percentage to 30 ± 10% (p < 0.0146) (Figure 1A). In contrast, the 50:50 mixture of L. xylanilyticus and B. cereus supernatants completely inhibited germination, showing values equivalent to zero throughout the assay (Supplementary Table 1).

Distribution graphs and germination speed index (GSI) of H. sabdariffa seeds under the following treatments: supernatant of L. xylanilyticus, supernatant of B. cereus, mixture of supernatants of L. xylanilyticus and B. cereus (50:50). Distilled water and sterilized LB broth were used as controls. (A) Distribution of treatments evaluated in germination. (B) Germination speed. A one-way ANOVA with Tukey’s multiple comparison test was used to compare the controls with the treatments. Significance was set at p < 0.05 (ns > 0.05; *< 0.05; ****< 0.0001).

A) Bar chart showing average germination across five treatments: distilled water, LB broth, L. xylanilyticus supernatant, B. cereus supernatant, and 50:50 mixture. L. xylanilyticus supernatant shows highest germination. B) Line graph illustrating germination speed index over seven days for the same treatments. L. xylanilyticus supernatant and LB broth show increased germination speed over time, while B. cereus and the 50:50 mixture show lower values.

The germination speed index (GSI) reflected behavior consistent with the total germination results (Figure 1B). Seeds treated with L. xylanilyticus supernatant achieved the highest GSI values from the third day onward, significantly exceeding the controls. Seeds treated with B. cereus supernatant showed slow and limited germination, while the 50:50 mixture showed no germination activity. Statistical analysis using one-way ANOVA followed by Tukey’s multiple comparison test confirmed significant differences between treatments (p < 0.05), highlighting the promoting effect of L. xylanilyticus supernatant and the inhibitory effect of B. cereus supernatant on the germination and germination rate of H. sabdariffa.

In the case of P. juliflora seeds, significant differences were only observed in the treatment of combined supernatants of L. xylanilyticus and B. cereus (50:50), resulting in a germination percentage of 90 ± 10%, compared to distilled water controls (33.33 ± 5.77%) (p < 0.0130) and LB broth (10 ± 0%) (p < 0.0003). The remaining treatments yielded germination percentages of 43.33 ± 5.77% for L. xylanilyticus based treatments and 33.33 ± 5.77% for B. cereus based treatments (Figure 2A).

Distribution graphs and germination speed index (GSI) of P. juliflora seeds under the following treatments: supernatant of L. xylanilyticus, supernatant of B. cereus, mixture of supernatants of L. xylanilyticus and B. cereus (50:50). Distilled water and sterilized LB broth were used as controls. (A) Distribution of treatments evaluated in germination. (B) Germination speed. A one-way ANOVA with Tukey’s multiple comparison test was used to compare the controls with the treatments. Significance was set at p < 0.05 (ns > 0.05; *< 0.05; ***< 0.001).

Panel A is a bar chart showing average germination across five treatments: distilled water, LB broth, L. xylanilyticus supernatant, B. cereus supernatant, and a 50:50 mixture. Significant differences are indicated by asterisks. Panel B is a line graph depicting germination speed index over seven days for the same treatments, with the 50:50 mixture showing the highest increase. Error bars display variability.

In terms of the germination speed index (GSI), the treatment with the combined supernatants of L. xylanilyticus and B. cereus (50:50) had the highest value of 9.00 ± 1.00, indicating an acceleration of the germination process compared to the other treatments. In contrast, the LB broth control showed the most significant inhibition of P. juliflora germination with an index of 1.33 ± 0.57 at 5 days (Figure 2B).

 Effect of <italic>Hibiscus sabdariffa</italic> and <italic>Prosopis juliflora</italic> growth with supernatants of <italic>L. xylanilyticus</italic> and <italic>B. cereus</italic>

The supernatants were analyzed to evaluate their effects on plant development, assessing stem size, leaf width, leaf length, and fresh weight. The observation period lasted four weeks, and the treatments were applied to the plants every seven days. The results showed that the LB broth control completely inhibited the development of both seedlings, so it was excluded from the statistical analyses. In H. sabdariffa plants, treatments based on L. xylanilyticus supernatants promoted greater growth in several plant parameters, showing a significant increase in stem size of 1.72 ± 0.21 mm (p < 0.004), leaf width of 8.20 ± 2.94 mm (p < 0.005), and fresh weight of 0.13 ± 0.06 g (p < 0.006) compared to the control (distilled water). The supernatant of B. cereus had no significant effects on any of the parameters evaluated. On the other hand, treatment with the 50:50 mixture of supernatants showed a positive effect only on leaf length of 12.60 ± 2.70 mm (p < 0.001), with no significant differences in the other parameters (Figures 3A–D).

Differences in the growth parameters of H. sabdariffa plants under the following treatments: supernatant of L. xylanilyticus, supernatant of B. cereus, mixture of supernatants of L. xylanilyticus and B. cereus (50:50). Distilled water was used as a control. (A) stem, (B) leaf width, (C) leaf length, and (D) fresh weight. A one-way ANOVA with Tukey’s multiple comparison test was used to compare the control with the treatments. Significance was set at p < 0.05 (ns > 0.05; *< 0.05; **< 0.01; ***< 0.001).

Boxplots show the effects of four treatments (distilled water, *L. xylanilyticus* supernatant, *B. cereus* supernatant, and a 50:50 mixture) on plant growth parameters: A) stem width, B) leaf width, C) leaf length, and D) fresh weight. Statistical significance between groups is indicated by asterisks: ns (not significant), * (p<0.05), ** (p<0.01), *** (p<0.001).

On the other hand, P. juliflora plants treated with L. xylanilyticus supernatants promoted greater growth in all parameters evaluated, showing a significant increase in stem length of 1.40 ± 0.10 mm (p < 0.005), leaf width of 8.92 ± 1.43 mm (p < 0.018), leaf length of 11.66 ± 1.15 mm (p < 0.0009), and fresh weight of 0.17 ± 0.01 g (p < 0.006) compared to the control (distilled water). The supernatant of B. cereus only showed a significant difference in leaf length with 8.66 ± 0.57 mm (p < 0.016). On the other hand, treatment with the 50:50 mixture of supernatants showed a positive effect on stem development of 1.32 ± 0.31 mm (p < 0.016) and leaf length of 10.33 ± 2.51 mm (p < 0.003) (Figures 4A–D). In summary, L. xylanilyticus proved to be the most effective treatment for improving the growth of both plants compared to the control and the other treatments.

Differences in the growth parameters of P. juliflora plants under the following treatments: supernatant of L. xylanilyticus, supernatant of B. cereus, mixture of supernatants of L. xylanilyticus and B. cereus (50:50). Distilled water was used as a control. (A) stem, (B) leaf width, (C) leaf length, and (D) fresh weight. A one-way ANOVA with Tukey’s multiple comparison test was used to compare the control with the treatments. Significance was set at p < 0.05 (ns > 0.05; *< 0.05; **< 0.01; ***< 0.001).

Four box plots comparing plant growth under different treatments: A) Stem diameter shows the highest increase with a 50:50 mixture, significant differences indicated by asterisks. B) Leaf width is also highest with the 50:50 mixture. C) Leaf length is significantly longer with L. xylanilyticus supernatant. D) Fresh weight is greatest with the 50:50 mixture. Each plot includes distilled water, L. xylanilyticus supernatant, B. cereus supernatant, and a 50:50 mixture treatments, with significance levels marked by asterisks. Phytochemical analysis of supernatants

The phytochemical content of the supernatants of both bacterial strains was characterized. Both supernatants showed low carbohydrate intensity, and in the case of L. xylanilyticus supernatants, low coumarin intensity was also detected. No other compounds evaluated were detected in the analyzed supernatants (Table 2).

Phytochemical composition of aqueous extracts of bacterial supernatants.

Classes SupernatantBacillus cereus SupernatantLysinibacillusxylanilyticus
Triterpenes − −
Coumarins − ++
Sesquiterpene lactones − −
Quinones − −
Saponins − −
Flavonoids − −
Tannins − −
Carbohydrates ++ ++
Alkaloids − −

++, low intensity 50%; −, negative reaction.

 Discussion

Microorganisms have become crucial contributors to sustainable agriculture by providing solutions to environmental problems (Manfredini et al., 2021). In this respect, postbiotics represent an environmentally friendly alternative for improving soil health and crop productivity (Panghal et al., 2022). In this study, we evaluated the effects of bacterial postbiotics derived from strains isolated from native soils of Nuevo León, Mexico, on the germination and early growth of Hibiscus sabdariffa and Prosopis juliflora. Cell-free supernatants from Lysinibacillus xylanilyticus and Bacillus cereus cultures were tested under controlled laboratory conditions. Our results showed that bacterial supernatants exert differential and significant effects on germination. In H. sabdariffa, the supernatant from L. xylanilyticus significantly increased germination (96.66 ± 5.77%, p < 0.0001), whereas the B. cereus supernatant significantly reduced it (30 ± 10%, p = 0.0146); the 50:50 mixture completely inhibited germination. These effects were consistently reflected in the germination speed index (p < 0.05).

In P. juliflora, only the mixed supernatant treatment (50:50) showed a significant effect, increasing germination (90 ± 10%) compared with both water (p = 0.0130) and LB broth controls (p < 0.0003), and also exhibiting the highest germination speed index (9.00 ± 1.00). On the other hand, treatments based on sterile LB broth completely inhibited the germination of Hibiscus sabdariffa. This inhibitory effect observed for LB control could mask or underestimate the actual impact of bacterial metabolites, which is why future research should use more refined alternative controls, such as uninoculated incubated medium or dialysed medium, to more accurately isolate the specific contribution of microbial metabolites.

Species of the genus Bacillus are widely associated with plant growth promotion through the production of high levels of ammonia, indolic compounds, gibberellins, and other metabolites (Vinodkumar et al., 2017; Shafi et al., 2017; Ongena and Jacques, 2008; Minaxi et al., 2012; Ge and Wei, 2023). However, these strains are known to produce beneficial compounds; they have also been found to synthesize antimicrobials such as cyclic lipopeptides, polyketides, and bacteriocins, which can influence seed or plant behavior (Keswani et al., 2020). In our study, the supernatant of B. cereus exhibited an inhibitory effect on the germination of H. sabdariffa. These results are consistent with those reported by Cabra Cendales et al. (2017), who found that the Bacillus subtilis strain GIBI 200 had no significant effect on tomato seed germination. Similarly, Hoang et al. (2005) reported that B. cereus extracts inhibited seedling growth in Lactuca sativa.

Rhizosphere-associated bacteria are known to inhibit plant growth through the direct or indirect release of allelochemicals into the rhizosphere (Barazani et al., 2001; Vacheron et al., 2013). This phenomenon has been documented in genera such as Bacillus, Pseudomonas, and Serratia, which produce volatile organic compounds (VOCs) that inhibit germination and root growth in Arabidopsis thaliana (Zhao et al., 2019; Luo et al., 2022). In contrast, Lysinibacillus spp. has been associated with beneficial activities for promoting plant growth, such as the solubilization of inorganic phosphorus into forms readily available for plant uptake (Ahsan et al., 2021). The seed microbiome, comprising microorganisms that inhabit both the interior and exterior of seeds, plays a crucial role in the germination process. These microbial communities, together with soil nutrients and rhizospheric microorganisms, can establish a beneficial coexistence that favors seed germination (Poppeliers et al., 2023; Ge and Wei, 2024; Papin et al., 2025). Multiple factors could explain the lack of increased germination observed in H. sabdariffa. Seed phenotypic differences are relevant in P. juliflora, which showed better germination performance under similar conditions. The above may be attributed to the greater resistance and adaptive capacity of P. juliflora seeds compared to H. sabdariffa (Sawal et al., 2004; Patnaik et al., 2017). Moreover, these bacteria can produce both plant growth-promoting compounds and antagonistic metabolites, which can potentially interfere with the seed microenvironment (Keswani et al., 2020; Esquivel et al., 2024). These results suggest that metabolites present in the evaluated bacterial supernatants can exert variable effects on the germination of the tested species, with a potential inhibitory action. Such responses are not uncommon, as antagonistic compounds have been reported in cell-free supernatants from growth-promoting bacteria (Naureen et al., 2017).

Significant differences (p < 0.05) were observed in the growth parameters of both plant species. L. xylanilyticus supernatants showed the most excellent postbiotic effect. In H. sabdariffa, significant increases were detected in leaf width (p = 0.029) and fresh weight (p = 0.029), while in P. juliflora, differences were observed in leaf length (p = 0.031), stem length (p = 0.034), and fresh weight (p = 0.008). These findings are consistent with previous studies, which reported that L. xylanilyticus has a biostimulant effect on spinach sprouts, increasing dry weight through the production of indole-3-acetic acid in all strains tested (Ahsan et al., 2021). Similarly, Lysinibacillus sp. (ZM1) has been shown to promote root growth in maize seedlings due to high auxin production (Pal et al., 2024). Moreover, L. sphaericus improved seedling vigor, germination rate, and shoot length in cucumber and tomato under greenhouse conditions (Naureen et al., 2017). These results highlight the high biostimulant potential of Lysinibacillus spp., which is attributed to the diverse metabolites they produce (Jamal and Ahmad, 2022; Pantoja-Guerra et al., 2023). The differences in the response to the treatments between P. juliflora and H. sabdariffa can be explained by their ecophysiological contrasts. P. juliflora is a highly adaptable species with strong tolerance to adverse environmental conditions, which may favor a more pronounced response to the extracellular metabolites present in the bacterial supernatants. In contrast, H. sabdariffa shows more specific germination requirements and greater sensitivity to environmental factors such as salinity and temperature (Taghvaei et al., 2022). Overall, these differences should be considered when extrapolating the applicability of the results to agricultural or ecological restoration contexts.

Bioactive compounds may be found among the molecules secreted during bacterial metabolism. Many of these molecules show various activities against pathogens, insects, pests, human diseases, and predators (Hussain et al., 2018). Or function as plant growth promoters like phytohormones (Egamberdieva and Teixeira da Silva, 2015). Natural coumarins have demonstrated both biological and allelopathic potential in a wide range of organisms and have been isolated from numerous microorganisms (Venugopala et al., 2013; Mondol et al., 2013; Costa et al., 2016). However, most studies have focused on their therapeutic effects due to their vigorous antimicrobial activity. Species of the genus Lysinibacillus are known to produce coumarins.

Furthermore, L. xylanilyticus CZ29 has been used as a probiotic, promoting plant growth by inhibiting harmful bacteria (Feng et al., 2021). Coumarins under iron-limiting conditions are secreted into the soil, where they reduce insoluble Fe3+ to soluble Fe2+, which can then be absorbed, thereby stimulating the growth of both plants and beneficial bacteria (Pieterse and Stringlis, 2023). In addition, these molecules function as signaling agents regulating interactions among commensals, pathogens, and plants (Reen et al., 2018; Yang et al., 2023).

In the present study, the qualitative detection of coumarin-like compounds in the cell-free supernatants of L. xylanilyticus should be interpreted as a preliminary finding, as the methods employed allow only the indication of the presence of certain classes of metabolites without enabling their structural identification or quantification. In this context, although the presence of coumarin-type compounds may be associated with the observed effects on plant germination and growth, a direct attribution of a specific physiological role to these molecules cannot be made. Therefore, the results suggest a potential contribution of extracellular metabolites to the detected biological effects, while highlighting the need for more comprehensive and targeted metabolomic analyses (LC-MS/MS or GC-MS) to identify the compounds responsible and to elucidate the underlying mechanisms of action. These results suggest that the mechanism of action involves providing antimicrobial protection against soil-borne pathogens while acting as signaling molecules that modulate plant growth responses, highlighting their potential as key bioactive compounds in strategies based on the addition of postbiotics for sustainable agriculture.

 Conclusion

Postbiotics have emerged as promising agents for supporting soil health. These compounds from microbial metabolism offer an alternative to conventional agrochemicals. This study evaluated the biostimulant effects of postbiotics produced by two native bacterial strains isolated from soils in Nuevo León, Mexico. The results show that L. xylanilyticus produces postbiotics that have a greater impact on the early growth of H. sabdariffa and P. juliflora, making it a promising candidate for studying its metabolites in plants application. In contrast, B. cereus postbiotics showed inhibitory effects when applied to seeds, demonstrating the importance of strain selection for application in plants or seeds. This study observed the distinct responses to postbiotics from native bacteria that can be used as an alternative to agrochemicals. These findings provide a foundation for the future development of biostimulant formulations using native strains, which are developed to enhance crop production productivity.

 Data availability statement

The original contributions presented in this study are included in this article/Supplementary material, further inquiries can be directed to the corresponding author.

 Author contributions

GR-A: Investigation, Resources, Writing – original draft, Formal analysis, Data curation, Writing – review & editing. RR-A: Writing – review & editing, Data curation, Conceptualization, Writing – original draft. ER-D: Project administration, Visualization, Writing – review & editing, Formal analysis, Methodology, Writing – original draft, Funding acquisition. AJ-G: Writing – review & editing, Methodology, Writing – original draft, Visualization, Supervision. AO-K: Software, Writing – original draft, Formal analysis, Writing – review & editing. ML-T: Writing – review & editing, Methodology, Resources, Conceptualization, Visualization, Writing – original draft. JG-R: Supervision, Writing – review & editing, Resources, Writing – original draft. LV-T: Resources, Writing – review & editing, Supervision, Investigation, Writing – original draft. AG-V: Data curation, Validation, Resources, Visualization, Methodology, Conceptualization, Project administration, Formal analysis, Investigation, Writing – review & editing, Funding acquisition, Supervision, Software, Writing – original draft. MG-G: Writing – review & editing, Funding acquisition, Resources, Writing – original draft, Investigation, Project administration, Data curation, Software, Visualization.

 Acknowledgments

We thank the Secretaría de Ciencia, Humanidades, Tecnología e Innovación (SECIHTI), for its invaluable support in strengthening and generating high-quality scientific knowledge.

 Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

 Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.

 Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

 Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fmicb.2025.1741549/full#supplementary-material

Graphical summary.

 References Ahsan N. Marian M. Suga H. Shimizu M. (2021). Lysinibacillus xylanilyticus strain GIC41 as a potential plant biostimulant. Microbes Environ. 36:ME21047. 10.1264/jsme2.ME21047 34744143 Arango M. C. Ruscitti R. Ronco R. Beltrano A. (2011). Mycorrhizal fungi inoculation and phosphorus fertilizer on growth, essential oil production and nutrient uptake in peppermint (Mentha piperita L.). Rev. Bras. Plantas Med. 14 692–699. 10.1590/S1516-05722012000400018 Barazani O. Friedman J. Cromack K. (2001). Allelopathic bacteria and their impact on higher plants. Crit. Rev. Microbiol. 27 41–55. 10.1080/20014091096693 11305367 Bhardwaj D. Ansari M. W. Sahoo R. K. Tuteja N. (2014). Biofertilizers function as key player in sustainable agriculture by improving soil fertility, plant tolerance and crop productivity. Microb. Cell Fact. 13:66. 10.1186/1475-2859-13-66 24885352 Cabra Cendales T. Rodríguez González C. A. Villota Cuásquer C. P. Tapasco Alzate O. A. Hernández Rodríguez A. (2017). Bacillus effect on the germination and growth of tomato seedlings (Solanum lycopersicum L.). Acta Biolo. Colomb. 22 37–44. 10.15446/abc.v22n1.57375 Canbolat M. Y. Bilen S. Çakmakçı R. Şahin F. Aydın A. (2006). Effect of plant growth-promoting bacteria and soil compaction on barley seedling growth, nutrient uptake, soil properties and rhizosphere microflora. Biol. Fertil. Soils 42 350–357. 10.1007/s00374-005-0034-9 Compant S. Duffy B. Nowak J. Clément C. Barka E. A. (2005). Use of plant growth-promoting bacteria for biocontrol of plant diseases: Principles, mechanisms of action, and future prospects. Appl. Environ. Microbiol. 71 4951–4959. 10.1128/AEM.71.9.4951-4959.2005 16151072 Costa T. M. Tavares L. B. B. de Oliveira D. (2016). Fungi as a source of natural coumarins production. Appl. Microbiol. Biotechnol. 100 6571–6584. 10.1007/s00253-016-7660-z 27364626 Egamberdieva D. Teixeira da Silva J. A. (2015). “Medicinal plants and PGPR: A new frontier for phytochemicals,” in Plant-growth-promoting rhizobacteria (PGPR) and medicinal plants, Vol. 42 eds Egamberdieva D. Shrivastava S. Varma A. (Cham: Springer), 1–14. 10.1007/978-3-319-13401-7_14 Esquivel N. H. Sagarnaga-Villegas L. M. Barrera-Perales O. T. Leos-Rodríguez J. A. A. Salas-González J. M. (2024). ROSELLE (Hibiscus sabdariffa L.) production in Mexico: Challenges and strategic prospects. Trop. Subtrop. Agroecosyst. 27:5124. 10.56369/tsaes.5124 Feng Y. H. Xiong J. Li Y. Zhang T. Cheng L. J. Jin L. Y. (2021). Effects of the inoculation of two different growth-promoting bacteria on the structure and diversity of microflora in tomato roots. Trop. Agric. 52, 6–8. 10.13651/j.cnki.fjnykj.2021.06.002 6404524 Ge M. Wei X. (2023). Spermosphere bacteria promote Ormosia henryi seed germination by activating metabolic pathways. Forests 14:1136. 10.3390/f14061136 Ge M. Wei X. (2024). Spermosphere bacterial community at different germination stages of Ormosia henryi and its relationship with seed germination. Sci. Hortic. 324:112608. 10.1016/j.scienta.2023.112608 Gómez-Govea M. A. García S. Heredia N. (2017). Bacterial metabolites from intra- and inter-species influencing thermotolerance: The case of Bacillus cereus and Geobacillus stearothermophilus. Folia Microbiol. 62 183–189. 10.1007/s12223-016-0487-2 27896600 Hakim S. Naqqash T. Nawaz M. S. Laraib I. Siddique M. J. Zia R. (2021). Rhizosphere engineering with plant growth-promoting microorganisms for agriculture and ecological sustainability. Front. Sustain. Food Syst. 5:617157. 10.3389/fsufs.2021.617157 Hijová E. (2024). Postbiotics as metabolites and their biotherapeutic potential. Int. J. Mol. Sci. 25:5441. 10.3390/ijms25105441 38791478 Hoang L. Joo G. J. Kim W. C. Jeon S. Y. Choi S. H. Kim J. W. (2005). Growth inhibitors of lettuce seedlings from Bacillus cereus EJ-121. Plant Growth Regul. 47 149–154. 10.1007/s10725-005-3217-3 Homthong M. Kaewpuk W. Yamsuan S. Thongsima A. Mokkapan K. Pikulthong V. (2022). Screening of indole-3-acetic acid PGPB from three agricultural systems at Nakhon Pathom, Thailand. Biodiversitas 23 5935–5941. 10.13057/biodiv/d231147 Hussain M. I. Qamar Abbas S. Reigosa M. J. (2018). Atividades e novas aplicações das cumarinas enquanto metabólitos secundários. Planta Daninha 36:16. 10.1590/s0100-83582018360100016 ISTA (2015). International rules for seed testing. Bassersdorf: International Seed Testing Association. Jamal Q. M. S. Ahmad V. (2022). Lysinibacilli: Biological factories intended for bio-insecticidal, biocontrol, and bioremediation activities. J. Fungi 8:1288. 10.3390/jof8121288 36547621 Keswani C. Singh H. B. García-Estrada C. Caradus J. He Y. W. Mezaache-Aichour S. (2020). Antimicrobial secondary metabolites from agriculturally important bacteria as next-generation pesticides. Appl. Microbiol. Biotechnol. 104 1013–1034. 10.1007/s00253-019-10300-8 31858191 Liakos K. G. Busato P. Moshou D. Pearson S. Bochtis D. (2018). Machine learning in agriculture: A review. Sensors 18:2674. 10.3390/s18082674 30110960 Lim H.-S. Kim Y.-S. Kim S.-D. (1991). Pseudomonas stutzeri YPL-1 genetic transformation and antifungal mechanism against Fusarium solani, an agent of plant root rot. Appl. Environ. Microbiol. 57 510–516. 10.1128/aem.57.2.510-516.1991 16348417 Luo H. Riu M. Ryu C. M. Yu J. M. (2022). Volatile organic compounds emitted by Burkholderia pyrrocinia CNUC9 trigger induced systemic salt tolerance in Arabidopsis thaliana. Front. Microbiol. 13:105090. 10.3389/fmicb.2022.105090 Maguire J. D. (1962). Speed of germination-aid in selection and evaluation for seedling emergence and vigor. Crop Sci. 2 176–177. 10.2135/cropsci1962.0011183X000200020033x Maia E. P. V. Garcia K. G. V. de Souza Oliveira Filho J. Pinheiro J. I. Filho P. F. M. (2023). Co-inoculation of rhizobium and arbuscular mycorrhiza increases Mimosa caesalpiniaefolia growth in soil degraded by manganese mining. Water Air Soil Pollut. 234:289. 10.1007/s11270-023-06314-8 Manfredini A. Malusà E. Costa C. Pallottino F. Mocali S. Pinzari F. (2021). Current methods, common practices, and perspectives in tracking and monitoring bioinoculants in soil. Front. Microbiol. 12:698491. 10.3389/fmicb.2021.698491 34531836 Minaxi G. Nain L. Yadav R. C. Saxena J. (2012). Characterization of multifaceted Bacillus sp. RM-2 for its use as plant growth promoting bioinoculant for crops grown in semi-arid deserts. Appl. Soil Ecol. 59 124–135. 10.1016/j.apsoil.2011.08.001 Mondol M. A. M. Shin H. J. Islam M. T. (2013). Diversity of secondary metabolites from marine Bacillus species: Chemistry and biological activity. Mar. Drugs 11 2846–2872. 10.3390/md11082846 23941823 Naureen Z. Rehman N. U. Hussain H. Hussain J. Gilani S. A. Al Housni S. K. (2017). Exploring the potentials of Lysinibacillus sphaericus ZA9 for plant growth promotion and biocontrol activities against phytopathogenic fungi. Front. Microbiol. 8:1477. 10.3389/fmicb.2017.01477 28861045 Olanrewaju O. S. Glick B. R. Babalola O. O. (2017). Mechanisms of action of plant growth promoting bacteria. World J. Microbiol. Biotechnol. 33:197. 10.1007/s11274-017-2364-9 28986676 Ongena M. Jacques P. (2008). Bacillus lipopeptides: Versatile weapons for plant disease biocontrol. Trends Microbiol. 16 115–125. 10.1016/j.tim.2007.12.009 18289856 Ordentlich A. Elad Y. Chet I. (1988). The role of chitinase of Serratia marcescens in biocontrol of Sclerotium rolfsii. Phytopathology 78 84–88. Pal G. Saxena S. Kumar K. Verma A. Kumar D. Shukla P. (2024). Seed endophytic bacterium Lysinibacillus sp. (ZM1) from maize (Zea mays L.) shapes its root architecture through modulation of auxin biosynthesis and nitrogen metabolism. Plant Physiol. Biochem. 212:108731. 10.1016/j.plaphy.2024.108731 38761545 Pandey K. D. Patel A. K. Singh M. Singh V. Kumari A. Jalaluddin S. (2020). “Secondary metabolites from bacteria and viruses,” in Natural bioactive compounds: Technological advancements, eds Sinha R. P. Häder D. P. (Amsterdam: Elsevier), 19–40. 10.1016/B978-0-12-820655-3.00002-1 Panghal A. Charan Singh Haryana C. Kumar Patra J. Gomes Cruz A. Gomes da Cruz A. Suri M. (2022). Postbiotics: From emerging concept to application. Front. Sustain. Food Syst. 6:887642. 10.3389/fsufs.2022.887642 Pantoja-Guerra M. Burkett-Cadena M. Cadena J. Dunlap C. A. Ramírez C. A. (2023). Lysinibacillus spp.: An IAA-producing endospore forming-bacteria that promotes plant growth. Antonie Van Leeuwenhoek 116 615–630. 10.1007/s10482-023-01828-x 37138159 Papin M. Polrot A. Breuil M. C. Czarnes S. Dreux-Zigha A. Le Roux X. (2025). Pre-sowing recurrent inoculation with Pseudomonas fluorescens promotes maize growth. Biol. Fertil. Soils 61 125–140. 10.1007/s00374-024-01873-2 Patnaik P. Abbasi T. Abbasi S. A. (2017). Prosopis (Prosopis juliflora): blessing and bane. Tropical Ecology, 58, 455–483. Available online at: https://www.researchgate.net/publication/322682224_Prosopis_Prosopis_juliflora_Blessing_and_bane (accessed June 12, 2025). Pieterse C. M. J. Stringlis I. A. (2023). Chemical symphony of coumarins and phenazines in rhizosphere iron solubilization. Proc. Natl. Acad. Sci. U. S. A. 120:e2304171120. 10.1073/pnas.2304171120 37094125 Poppeliers S. W. Sánchez-Gil J. J. de Jonge R. (2023). Microbes to support plant health: Understanding bioinoculant success in complex conditions. Curr. Opin. Microbiol. 73:102286. 10.1016/j.mib.2023.102286 36878082 Poveda J. González-Andrés F. (2021). Bacillus as a source of phytohormones for use in agriculture. Appl. Microbiol. Biotechnol. 105 8629–8645. 10.1007/s00253-021-11492-8 34698898 Reen F. J. Gutiérrez-Barranquero J. A. Parages M. L. O’Gara F. (2018). Coumarin: A novel player in microbial quorum sensing and biofilm formation inhibition. Appl. Microbiol. Biotechnol. 102 2063–2073. 10.1007/s00253-018-8787-x 29392389 Romero-Arguelles R. Romo-Sáenz C. I. Tamez-Guerra P. Fonseca-Rivera D. Elizondo-Luevano J. H. Rodriguez-Garza N. E. (2025). In vitro and in vivo antitumor activity of a chloroform partition from Ibervillea sonorae (S. Watson) Greene endophytic Bacillus subtilis extracts. Plants 14:1474. 10.3390/plants14101474 40431040 Sansinenea E. Ortiz A. (2011). Secondary metabolites of soil Bacillus spp. Biotechnol. Lett. 33 1523–1538. 10.1007/s10529-011-0617-5 21528405 Santiago H. S. Aranda-Ocampo S. Hernández-Morales J. Peña-Lomeli A. (2020). Effect of Bacillus spp. on the germination and growth of roselle plants (Hibiscus sabdariffa L.). Agro Productividad 13:1743. 10.32854/agrop.v13i10.1743 Sawal R. K. Ratan R. Yadav S. B. S. (2004). Mesquite (Prosopis juliflora) pods as a feed resource for livestock - A review. Asian-Australas. J. Anim. Sci. 17 719–725. 10.5713/ajas.2004.719 Sayyed R. Z. Chincholkar S. B. Reddy M. S. Gangurde N. S. Patel P. R. (2013). “Siderophore producing PGPR for crop nutrition and phytopathogen suppression,” in Bacteria in agrobiology: Disease management, ed. Maheshwari D. (Berlin: Springer), 291–304. 10.1007/978-3-642-33639-3_17 Shafi J. Tian H. Ji M. (2017). Bacillus species as versatile weapons for plant pathogens: A review. Biotechnol. Biotechnol. Equip. 31 446–459. 10.1080/13102818.2017.1286950 Shah D. Khan M. S. Aziz S. Ali H. Pecoraro L. (2022). Molecular and biochemical characterization, antimicrobial activity, stress tolerance, and plant growth-promoting effect of endophytic bacteria isolated from wheat varieties. Microorganisms 10:21. 10.3390/microorganisms10010021 35056470 Smyth E. M. McCarthy J. Nevin R. Khan M. R. Dow J. M. O’Gara F. (2011). In vitro analyses are not reliable predictors of the plant growth promotion capability of bacteria; a Pseudomonas fluorescens strain that promotes the growth and yield of wheat. J. Appl. Microbiol. 111 683–692. 10.1111/j.1365-2672.2011.05079.x 21672102 Taghvaei M. Nasrolahizadehi A. Mastinu A. (2022). Effect of light, temperature, salinity, and halopriming on seed germination and seedling growth of Hibiscus sabdariffa under salinity stress. Agronomy 12:2491. 10.3390/agronomy12102491 Vacheron J. Desbrosses G. Bouffaud M. L. Touraine B. Moënne-Loccoz Y. Muller D. (2013). Plant growth-promoting rhizobacteria and root system functioning. Front. Plant Sci. 4:356. 10.3389/fpls.2013.00356 24062756 Van Staden J. Ngoroyemoto N. Kulkarni M. G. Stirk W. A. Gupta S. Finnie J. F. (2020). Interactions between microorganisms and a seaweed-derived biostimulant on the growth and biochemical composition of Amaranthus hybridus L. Nat. Prod. Commun. 15 1–9. 10.1177/1934578X20934228 Vasseur-Coronado M. du Boulois H. D. Pertot I. Puopolo G. (2021). Selection of plant growth promoting rhizobacteria sharing suitable features to be commercially developed as biostimulant products. Microbiol. Res. 245:126672. 10.1016/j.micres.2020.126672 33418398 Venugopala K. N. Rashmi V. Odhav B. (2013). Review on natural coumarin lead compounds for their pharmacological activity. Biomed Res. Int. 2013:963248. 10.1155/2013/963248 23586066 Vinodkumar S. Nakkeeran S. Renukadevi P. Malathi V. G. (2017). Biocontrol potentials of antimicrobial peptide producing Bacillus species: Multifaceted antagonists for the management of stem rot of carnation caused by Sclerotinia sclerotiorum. Front. Microbiol. 8:446. 10.3389/fmicb.2017.00446 28392780 Xu F. Liao H. Yang J. Zhang Y. Yu P. Cao Y. (2023). Auxin-producing bacteria promote barley rhizosheath formation. Nat. Commun. 14:40916. 10.1038/s41467-023-40916-4 37726263 Yang Y. Xu J. Li Y. He Y. Yang Y. Liu D. (2023). Effects of coumarin on rhizosphere microbiome and metabolome of Lolium multiflorum. Plants 12:1096. 10.3390/plants12051096 36903956 Zhao P. Li P. Wu S. Zhou M. Zhi R. Gao H. (2019). Volatile organic compounds (VOCs) from Bacillus subtilis CF-3 reduce anthracnose and elicit active defense responses in harvested litchi fruits. AMB Express 9:119. 10.1186/s13568-019-0841-2 31352537 Zuluaga M. Y. A. Milani K. M. L. Miras-Moreno B. Lucini L. Valentinuzzi F. Mimmo T. (2021). Inoculation with plant growth-promoting bacteria alters the rhizosphere functioning of tomato plants. Appl. Soil Ecol. 158:103784. 10.1016/j.apsoil.2020.103784

Edited by: Debasis Mitra, Graphic Era University, India

Reviewed by: Elizabeth Temitope Alori, Landmark University, Nigeria

Andrea Mastinu, University of Brescia, Italy