Global warming induces climate change, increases global temperature, elevates atmospheric carbon dioxide, and changes precipitation patterns. It is the biggest threat to ecosystems and biodiversity (Allen et al., 2010). These changes increase drought, soil salinity, flooding, weeds, and pests, directly impacting crops and agriculture’s growth and development (FAO, 2009). Drought is expected to be the leading cause of reduced crop production by 2050 (Vinocur and Altman, 2005). After Nevada, Utah is considered to be the second driest state in the United States (Utah Department of Public Safety). On top of that, anthropogenic abuses and an increased frequency of extreme weather negatively affect soil health. Chemical fertilizers are used extensively to enhance crop production. However, adding these to the soil affects soil health and crop production through sanitization, water pollution, organic matter, and high costs (Olanrewaju et al., 2017; Pahalvi et al., 2021).

Landscaping, the major consumer of irrigation water, is an essential section of agriculture prone to adverse effects caused by environmental stresses. Recent studies using crop water demand and green water availability projections under changing climates have shown that we can adapt agriculture to green water scarcity through various management strategies and have the potential to promote global food security (He and Rosa, 2023). Promoting and using native plants in urban landscaping is in demand in arid urban areas in China (Liu et al., 2024). Native plants that grow in their natural habitat with little human intervention are promising in low-water landscapes (Rupp and Wheaton, 2014). The degraded lands, wildlife habitats, and wetlands have been restored by using these native plants (Hooper et al., 2005). The U.S. Intermountain West is rich in drought-tolerant woody and herbaceous native plants, which can symbiotically interact with actinobacteria Frankia and fix atmospheric nitrogen (Benson, 1982; Kratsch and Graves, 2004; Kratsch, 2011). Most of Utah is a wilderness rich in native plants and endemic species. Native plants are of keen interest to the Green Industry as they have traits adapted to their native environments, including drought and salt tolerance. Desert and dry-land native plant species are adapted to arid and semiarid conditions because of their deep root systems and are insect and fungi-resistant. They need less harsh chemicals such as fertilizers and pesticides that may harm natural environments and soil. Some native plants are recommended for low-water landscaping (Mee et al., 2003; Kratsch, 2011; Rosentreter et al., 2017). Although some native plants do very well in the wild, they are challenging to grow in a nursery or landscape environment. One possible reason for this could be a lack of natural symbioses with soil microorganisms in the landscape. For example, Ceanothus velutinus (snowbrush ceanothus) is challenging to propagate for nursery production and is recognized as an actinorhizal plant. They have a wide range of distribution from 2133- 2743 m elevation. The seeds of this plant show 80-90% germination if adequately collected and treated (Rupp and Wheaton, 2014). The roots of snowbrush ceanothus cutting are susceptible to rotting, and therefore, it is challenging to grow from cuttings in a propagation mix (Rupp and Wheaton, 2014). One possible reason for this failure to propagate could be the lack of native soil microbiome in the landscape media.

Soil is known as the most diverse and complex microbial ecosystem on the land (Crowther et al., 2019). The soil microbe-plant interactions are complex and are significant in plants’ growth and development (Lugtenberg and Kamilova, 2009). One gram of soil contains around 10 billion diverse microbes in and around the plant roots (Yadav et al., 2017). Plants secrete high or low molecular weight organic compounds as root exudates in the soil that attract the selective bacteria and colonize (Walker et al., 2003). A Study has shown that Pseudomonas stutzeri NRCB010 induces certain exudates from the roots of Tomato, which enhances the microbe’s colonization in the rhizosphere (Zhang et al., 2023). The microbe in the bulk soil around the roots acts as an inoculum and directs microbes to colonize the rhizosphere and roots (Bulgarelli et al., 2015). The microbes inhabiting the rhizosphere or roots, which can be bacteria, fungi, and viruses, exhibit several plant growth-promoting traits like phosphate solubilization, Indole-3-acetic acid (IAA), Nitrogen fixation, siderophore, catalase, ammonia production, ACC deaminase and protease activity and help plant’s growth and development (Mohanty et al., 2021).

Many PGPR are known to produce phytohormones like auxin, cytokinin, and several volatile organic compounds (VOC) that promote plant growth and help plants mitigate various biotic and abiotic stresses (Orozco-Mosqueda et al., 2023). They have also been shown to increase shoot length and diameter (Karlidag et al., 2007; Karakurt and Aslantas, 2010). IAA is a prominent member of the phytohormone auxin in plants and controls many plant growth activities, from root architecture to fruit and embryo development, phototropism, geotropism, apical dominance, leaf formation, and abscission (Srivastava, 2002). The tryptophan-dependent pathway is the best-understood pathway of IAA production in plants and microbes (Zhao, 2010). Natural and synthetic auxins such as IAA, IBA, naphthaleneacetic acid (NAA), and 2,4-dichlorophenoxyacetic acid (2,4-D) are in regular use for plant cells, tissue, and organ cultures to elicit specific morphogenetic responses, such as callusing and rooting However, IAA is very unstable; still, it is used for plant tissue cultures (Nissen and Sutter, 1990). Bacteria can improve overall plant health by producing IAA that can induce root architecture alterations that enhance water and nutrient uptake (Glick, 2012; Pii et al., 2015; Etesami et al., 2015b). In addition, bacterial IAA helps plants mitigate abiotic stresses such as drought, salinity, and heavy metal toxicity (Etesami and Glick, 2024). Besides, IAA PGPR has shown the ability for nutrient uptake, such as the ability to solubilize phosphate, nitrogen fixation, and siderophore, protease, and catalase production (Kumar et al., 2022). Besides all these plant growth-promoting traits in microbes, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase enzyme activity in several bacteria is helpful for plants to deal with ethylene stress. ACC is the precursor for the stress hormone ethylene in plants. ACC deaminase cleaves the ACC into ammonia and α-ketobutyrate and inhibits ethylene production. The microorganism with this enzyme activity in the rhizosphere reduces plant ethylene levels, inhibits its detrimental effects, and protects against biotic and abiotic stresses (Glick, 2014). Several plant growth-promoting bacteria have been isolated from the rhizosphere of pineapple from various stress-inducing habitats (Ratnaningsih et al., 2023).

Snowbrush ceanothus rhizosphere has a rich microbiome containing several plant-promoting bacteria that showed several plant growth-promoting characteristics such as IAA, catalase and siderophore production, phosphate solubilization, and the ability to fix nitrogen (Ganesh et al., 2022). The majority of rhizobacteria belonged to Pseudomonas and Streptomyces. However, there is a variety of PGPR belonging to Bacillus, Peribacillus, Variovorax, Xenophilus, Brevundimonas, Pantoea, Ancylobactor, and Priestia exhibiting various plant growth-promoting traits, including IAA, siderophore, and catalase production (Ganesh et al., 2022). We hypothesize that the native soil of snowbrush ceanothus harbors many growth-promoting bacteria that produce IAA, which can help the propagation of snowbrush ceanothus in greenhouse conditions and colonize the rhizosphere. In this study, we investigated the effect of bulk soil of the snowbrush ceanothus plants from Logan Canyon as inoculum on the cutting propagation of the snowbrush ceanothus in the greenhouse. We also isolated the IAA-producing rhizobacteria from the surviving cuttings and assessed them seven other PGP traits. Subsequently, we tested their ability to promote plant growth in Arabidopsis.

Snowbrush ceanothus is a challenging native plant to propagate in landscape (Rupp and Wheaton, 2014). A recent study showed several PGPR in the rhizosphere of native soil-treated greenhouse-grown ceanothus plants (Ganesh et al., 2022). This study revealed the inoculation of native soil to the propagation mix with Hormodin-2 to snowbrush ceanothus cuttings in the greenhouse showed visually longer and denser roots and a higher survival rate of 33% in June and 50% in July ( Supplementary Figure 1 and Figure 2A ). In soybeans, a study showed that inoculation of soybean seeds with a consortium of indigenous microbes from the adult healthy plants from two different managed soils benefited the seedling growth (May et al., 2023). In another study, the native soil from different crops, such as maize wheat, ryegrass, and sweet potato, was used to inoculate rice plants. This inoculation led to isolating wheat and maize-derived plant growth bacteria, significantly promoting rice plant growth (Habibi et al., 2014).

Various studies reported that PGPR promotes a plant’s root growth by producing indole acetic acid (IAA), an auxin known to regulate root growth and architecture (Vacheron et al., 2013; Grover et al., 2021). We isolated the IAA-producing bacterial isolates from the survived cuttings in the next step, and all isolates except for two isolates, CK-7 and CK-11, produced IAA more than 1 µg/mL. A rice seedling study upon inoculation with rhizosphere and endophytic isolates from rice plant roots reported that the “IAA may be the first PGP trait” for isolation of PGPB (Etesami et al., 2015a). Another study isolated the IAA-producing bacteria from banana, cotton, maize, and wheat rhizosphere. In pot experiments, these isolates showed significant growth promotion in wheat seedlings (Mohite, 2013).

All isolates except CK-1 could grow on DF media, which has ACC as a nitrogen source and may possess ACC deaminase activity. ( Figure 3B ; Table 2 ). Four isolates, CK-6, CK-40, CK-53, and CK-55, grow exclusively on DF media, showing that they possess ACC deaminase activity and can grow on ACC as a nitrogen source. CK-6 and CK-53 were identified as Pseudomonas, CK-40 is Klebsiella sp., and CK-55 is Sphingobium sp. However, four isolates, CK-3, CK-20, CK-22, and CK-24, grow moderately on the DF media. CK-24 was identified as Bacillus sp., CK-20 was identified as Massilia sp., and CK-3 and CK-22, were identified as Pseudomonas sp. The eight isolates grow mildly on DF media ( Figure 3B ). Klebsiella strain IG 3 was isolated from the wheat rhizosphere, exhibiting ACC deaminase activity and imparting salt tolerance in oat seedlings (Sapre et al., 2018). ACC deaminase-producing Pseudomonas were isolated from the rhizosphere soil of grapevine (Vitis vinifera L.) in arid regions of China. Most of these isolates were identified as Pseudomonas sp. One of the isolates, P. corrugata, weakens the drought-induced growth inhibition in grapevines (Duan et al., 2021). A study reported four ACC deaminase-producing P. fluorescence strains improved sweet corn productivity under limited water availability (Zarei et al., 2020). B. mojavensis PRN2 from the pea nodules exhibit ACC deaminase activity (Maheshwari et al., 2020). Similarly, three salt-tolerant isolates, B. subtilis (NBRI 28B), B. subtilis (NBRI 33 N), and B. safensis (NBRI 12 M), are reported to promote plant growth and modulate ethylene metabolism to impart salt tolerance in maize (Misra and Chauhan, 2020). Further characterization of these isolates for ACC deaminase activity and drought tolerance can lead to the development of bio stimulants.

One isolate, CK-1, belongs to Chryseobacterium sp. and showed extreme protease activity on skim milk agar along with siderophore, ammonia, and IAA production. Chryseobacterium soil isolates are known to have several plant-promoting traits, such as IAA, HCN, and antifungal production, and ACC deaminase activities make them useful in crop production. Besides, many species of Chryseobacterium have characteristics of degradation of aromatic compounds and play an essential role in industrial use (Nishioka et al., 2016). Chryseobacterium isolates from the metal-contaminated site can produce IAA, HCN, and ammonia and promote maize growth in greenhouse experiments (Marques et al., 2010). Similarly, Chryseobacterium isolates are known to deamidate proteins, produce proteases, and be used as bioremediation/biodegradation agents (Yamaguchi and Yokoe, 2000; Wang et al., 2008).

Isolate CK-20 was identified as Massilia sp. This isolate tested positive for IAA, ammonia production, ACC deaminase, and protease activity. Massilia sp. produce many components, such as synthesizing violacein, a natural antibiotic that is effective on malaria, diarrhea, and even tumors, and polyhydroxyalkanoate (PHAs), a kind of natural polymer biomaterial (Agematu et al., 2011; Han et al., 2014). Several Massilia sp. have been reported to act as a bioremediation agent and degrade toxic gas components like benzene, toluene, ethylbenzene, and xylene isomers in air and soil contaminants such as phenanthrene and chloroacetamide herbicides (Lou et al., 2016; Lee et al., 2017; Gu et al., 2021; Son et al., 2021). Massilia bacteria can also promote plant growth and increase the survival rate of plants in harsh environments. When Massilia was applied along with arbuscular mycorrhizal fungi, it alleviated the salt stress on plant growth, root colonization, and nutrient accumulation in corn plants in coastal reclamation areas (Krishnamoorthy et al., 2016).

Two isolates, CK-24 and CK-54, belong to the genus Bacillus. The isolate CK-24 can produce IAA and ammonia and grow on DF and nitrogen-free media. However, CK-54 can solubilize phosphate, show IAA, protease, and ammonia production, and grow on DF media. Like Pseudomonas, Bacillus is also a widely used PGPR because of its various PGP traits and serves as biocontrol. Different Bacillus species have been used worldwide as PGPR. Bacillus is biocompatible with other genera, like nitrogen fixer Azospirillum and Azotobacter, and is used as a co-inoculant in the consortia of bacteria (Kashyap et al., 2019). B. subtilis has been reported to suppress pathogens and mitigate biotic stress in plants (Hashem et al., 2019).

One isolate, CK-40, was identified as Klebsiella. This isolate produces the highest level of IAA with 41^±0.40µg/mL. It also showed an ability to grow on DF media, fix nitrogen, and solubilize phosphate, ammonia, and catalase production. The whole genome sequence analysis and other studies of a PGPR Klebsiella sp. D5A isolate from tall fescue roots revealed this bacterium’s PGPR, salinity-tolerant, and alkalotolerant properties (Liu et al., 2016). Another study showed that inoculating maize plants in greenhouse conditions with PGPR from Klebsiella isolates enhanced vegetative growth, nitrogen fixation, and nitrogen mobilization (Kuan et al., 2016).

The isolate CK-55 was identified as Sphingobium sp. This isolate can fix nitrogen, have vigorous ACC deaminase activity, and produce ammonia and catalase. Sphingobium belongs to the class Alpha-proteobacteria and is well-known for its pollutant bioremediation and biodegradation activities (Takeuchi et al., 2001). Sphingobium sp. strain AEW4 showed growth promotion in beachgrass and other plants, and comparative genomics analysis of its genome revealed several plant growth-promoting characteristics (Boss et al., 2022). Another strain of Sphingobium- DI-6 isolated from the diazinon-contaminated soil showed the capability to metabolize it as a carbon source and can be a potential candidate for diazinon bioremediation (Wang et al., 2022). Thus, CK-55 isolate can be a potential candidate for bioremediation and plant growth-promoting activities.

Eight bacterial isolates of 17 isolates, CK-6, CK-22, CK41, CK-44, CK-47, CK-50, CK-53, and CK55, showed a significant increase in the shoot biomass of A. thaliana ( Figure 4 ). All isolates except CK-55 were identified as Pseudomonas. The CK-55 isolate identified as Sphingobium sp. ( Table 1 ). All isolates showed IAA, siderophore and catalase production, phosphate solubilization, and nitrogen fixation abilities. Isolate CK-50 and CK-53 showed all the PGP traits tested in this study ( Table 2 ). CK-53 showed a very vigorous growth on skim milk agar. Pseudomonas is the most investigated genus for plant growth-promoting characteristics and harboring many traits (Nadeem et al., 2016). Pseudomonas is one of the strong phosphates solubilizers among PGPR, and the gene responsible for mineral phosphate solubilization has been cloned from Pseudomonas isolate P. cepacia (Babu-Khan et al., 1995; Rodrı́guez and Fraga, 1999). In an iron-deficient environment, the Pseudomonas produce siderophore, enhancing iron availability for plant uptake (Rachid and Bensoltane, 2005).

Pseudomonas strains also reported mitigating various plant stresses because of different stress-related plant growth-promoting traits. A study has shown that P. fluorescens helps pea plants survive well in drought due to the better ability to colonize in the roots than P. putida. (Arshad et al., 2008). In contrast, the production of antifreeze protein by P. putida GR12-2 helped protect the canola plant from chilling injury(5°C) (Sun et al., 1995). Several ACC-deaminase enzymes-producing Pseudomonas sp. have been reported (Gupta and Pandey, 2019; Pandey and Gupta, 2020; Khan and Singh, 2021). Besides, various studies reported the presence of nitrogenase gene/island in Pseudomonas and their nitrogen-fixing capabilities (Krotzky and Werner, 1987; Yan et al., 2008; Li et al., 2017). Pseudomonades are well known to produce extracellular proteases. Various studies reported the biocontrol activities of different Pseudomonas sp. against plant pathogens due to their protease activities (Siddiqui et al., 2005; Durairaj et al., 2017; Ghadamgahi et al., 2022).

Snowbrush ceanothus is an evergreen actinorhizal plant that can fix atmospheric nitrogen and tolerate drought and heat. It is used in low-water-use landscaping and contains several plant growth-promoting bacteria but is difficult to propagate. The inoculation of bulk soil from the native location of snowbrush ceanothus to the cutting propagation mix promoted the cutting’s survival rate. The rhizobacteria isolated from these cuttings showed a high IAA production level and various plant growth-promoting characteristics like nitrogen fixation, phosphate solubilization, catalase, ammonia, and siderophore production, protease, and ACC deaminase activities. 50% of the isolates belong to Pseudomonas, and the other isolates identified as Bacillus, Chryseobacterium, Massilia, Klebsiella, and Sphingobium sp. The inoculation of eight bacterial isolates, CK-6, CK-22, CK41, CK-44, CK-47, CK-50, CK-53, and CK55, significantly increase the shoot biomass of A. thaliana. All except one CK-55 belong to Pseudomonas, CK-55 identified as Sphingobium sp. In this study, two of them, CK-50 and CK-53, exhibit all eight PGP traits. We are investigating these eight PGPR on maize, tall fescue, watermelon, and wheat for growth promotion under abiotic stresses. We are also testing these microbes for the cutting propagation of snowbrush ceanothus.

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/ Supplementary Material .

JG: Writing – review & editing, Validation, Methodology, Investigation, Formal analysis, Data curation. KH: Writing – review & editing, Validation, Methodology, Investigation, Formal analysis, Data curation. AD: Writing – review & editing, Validation, Methodology, Formal analysis. TW: Writing – review & editing, Methodology, Data curation. AK: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.