The bacteriological green synthesis of silver nanoparticles (AgNPs) is a promising, cost-effective, and environmentally friendly approach in nanobiotechnology. This process leverages the ability of bacteria to reduce silver ions (Ag⁺) to produce nanoparticles with unique properties, including antimicrobial, anticancer, and bioremediation efficiency (Dayma et al., 2024). This biogenic method is superior to traditional chemical and physical synthesis because it avoids hazardous chemicals and offers biocompatibility (Dhaka et al., 2023; Huq et al., 2023; Singh et al., 2015). This aligns with the broader scientific trend of using biological systems for their environmental advantages and the unique characteristics they impart to the resulting nanoparticles (Junejo et al., 2024; Manisekaran et al., 2024; Renjusha and Kumar, 2023).

Bacteria in the Bacillus genus, such as Bacillus mojavensis and Bacillus pumilus, produce biocatalysts and secondary metabolites that act as reducing and capping agents, ensuring the synthesis of stable and uniform nanoparticles (Iqtedar et al., 2019; Mahmoud et al., 2016). Additionally, the use of bacterial biomass or cell-free extracts simplifies the process, as extracellular synthesis is favoured over intracellular production for easier nanoparticle isolation (Saritha and Prabha, 2022; Singh and Mijakovic, 2022).

Rooftop photovoltaic solar panels host diverse microbial communities adapted to extreme conditions like high solar radiation, temperature fluctuations, and desiccation (Luhana et al., 2025; Moura et al., 2021). Cyanobacterial genus Chroococcidiopsis isolated from solar panels in Valencia, Spain, and exhibited resistance to desiccation and UV-C radiation, suggesting potential applications in astrobiology and biotechnology (Baldanta et al., 2023). Stress-resistant genera like Hymenobacter and Deinococcus are prevalent (Porcar et al., 2018; Tanner et al., 2020). Majority of these bacteria are capable of producing pigments like carotenoids, which imparts antioxidant properties, making them candidates for novel antioxidant applications (Luhana et al., 2025; Tanner et al., 2019). The microbial colonization of solar panels is subjected to environmental factors and fluctuations affecting species richness and diversity (Tanner et al., 2020). Biofilm-producing bacteria on solar panels can impact system efficiency through soiling (Ortiz et al., 2024). Despite this, these panels are a promising source of microorganisms with genes for novel extremozymes, pigments, and secondary metabolites, particularly those involved in stress resistance and biofilm formation (Jotta et al., 2024; Ortiz et al., 2024). The functional profiles of these bacterial communities are consistent across different geographical zones, highlighting their adaptability and opening new dimensions for biotechnological applications (Dorado-Morales et al., 2016; Tanner et al., 2018). Overall, the study of microbial diversity on solar panels enriches our knowledge and understanding of microbial life growing under extreme conditions and opens new dimensions for manipulating these organisms for various biotechnological applications.

Kocuria flava derived silver nanoparticles represent a promising approach in green synthesis. A study on a marine isolate of K. flava focused on using its extracellular metabolites to synthesize and characterize AgNPs. These nanoparticles showed strong antibacterial activity, particularly a synergistic effect with the antibiotic ciprofloxacin against multi-drug resistant strains like P. aeruginosa and E. coli (Farhan and Shareef, 2024). The integration of this bacteriogenic synthesis with traditional and advanced applications of AgNPs could lead to advancements in nanomedicine (Mohanata et al., 2023).

The characterization of bacteriologically produced silver nanoparticles (AgNPs) is crucial for understanding their properties. Various analytical tools are used, including UV–vis spectroscopy to confirm AgNP formation (Deljou and Goudarzi, 2016; Wypij et al., 2021). SEM and TEM confirm their size (typically 5–50 nm) and shape (most often spherical) (El-Naggar et al., 2024). Additionally, Fourier transform infrared spectroscopy is used to identify the biomolecules responsible for capping and stabilization (Jain et al., 2021), while X-ray diffraction and dynamic light scattering confirm their crystalline properties, size distribution, and stability (Rosman et al., 2020).

The biotechnological application of synthesized AgNPs largely depends on the bacteria used for production. For instance, a consortium of Lactobacillus sp. and Bacillus sp. synthesized AgNPs (4.65 to 22.8 nm) with significant antimicrobial efficiency against multi-drug resistant S. aureus and P. aeruginosa (Al-Asbahi et al., 2024). Similarly, AgNPs from Klebsiella pneumoniae, Micrococcus luteus, and Enterobacter aerogenes were effective in bioremediation and antimicrobial applications (Patel et al., 2024). Klebsiella pneumoniae mediated synthesis of AgNPs also demonstrated efficient dye removal and antibacterial activities (Desai et al., 2024). In another study, AgNPs (82.76 nm) from Pseudomonas otitidis showed moderate antibacterial and antibiofilm activities (Jose et al., 2024). Geobacillus spp. synthesized AgNPs, mostly under 100 nm, that were spherical and stable (Cekuolyte et al., 2023). Other studies have shown that Paenibacillus sp. can promptly synthesize AgNPs (15–55 nm) with bactericidal activities against Salmonella enteritidis and Candida albicans (Huq et al., 2023). Together, these studies highlight the versatility of bacterial sources for the biomanufacturing of AgNPs, offering a sustainable alternative to conventional methods and opening up new avenues for applications in anti-cancer therapy, antimicrobial activity, and bioremediation aligning with SDGs.

The immense potential of green-synthesized AgNPs lies in their diverse applications. In antimicrobial therapy (Deljou and Goudarzi, 2016). AgNPs are effective against pathogenic strains like S. aureus (MRSA) and P. aeruginosa by disrupting cell membranes, blocking DNA replication, and producing reactive oxygen species (ROS) (Huq et al., 2023; Mahmoud et al., 2016). Furthermore, they show promise in cancer treatment, inducing apoptosis in cancerous cells and enhancing the efficacy of chemotherapeutic drugs (Sintubin et al., 2012; Wypij, 2021).

AgNPs also have potential in agricultural applications, where they have been shown to enhance seed germination and protect crops from bacterial diseases (Singh et al., 2015). Their bioremediation efficiency is also significant, as they can facilitate the degradation of organic and inorganic pollutants (Ibrahim et al., 2021; Yamini and Rajeswari, 2023). Additionally, due to their biocompatibility and unique optical properties, AgNPs are being used in biosensors, drug delivery, and wound healing (Dhaka et al., 2023; Paterlini et al., 2021).

While AgNPs have been biosynthesized using K. flava before, our study is the first to report isolation of a strain of K. flava from a photovoltaic panel which demonstrate a specific anti-cancer efficacy against blood cancer cell lines, antimicrobial potential, and also antibiotic removal from waste water. All the potential applications aligning with Sustainable Development Goals (SDGs) 6, 9, 11, and 13.

This investigative inquiry focused on the microbial assemblage established on photovoltaic panels, wherein a distinct strain exhibiting a vibrant yellow colony and pronounced biofilm production capabilities was identified. Supporting evidence was provided by Tanner et al. (2019), who noted that numerous isolates derived from photovoltaic solar panels, particularly those cultured on marine agar (Zobell), exhibited pigmentation in hues of pink, red, and orange. In a similar vein, Dorado-Morales et al. (2016) discovered that a range of solar panel isolates cultivated using R2A agar displayed pink, red, orange and yellow pigmentation.

The bacterial isolate K. flava KKYHNGU1 has demonstrated its potential as a candidate for various applications due to its exceptional resistance properties, tolerating salt concentrations (w/v) between 1–9%, prolonged UV radiation exposure (8 min), alkaline condition (pH 9), and survival at temperatures reaching as high as 55 °C. Conversely, According to Dorado-Morales et al. (2016) a limited number of solar panel isolates exhibited resistance to extreme thermal conditions and acidic pH, while many of these isolates displayed the capability to endure elevated sodium chloride concentrations (up to 30% w/v) and substantial UV radiation. The influences of temperature and pH on the proliferation of Chroococcidiopsis spp. were also examined by Baldanta et al. (2023), reported that cultures experienced bleaching by the end of second day at about 50 °C, with no isolates demonstrating growth in liquid media. Furthermore, statistical evaluation revealed that although cultures maintained their original pigmentation green and remain alive long after 240 h (about 10 full days) at around 40 °C, growth exhibited significant reduction at both 4 °C as well as at 40 °C. All isolates demonstrated optimal growth at a pH of 7.5, which is near to physiological value.

Bacteriological bio-manufacturing of silver nanoparticles (AgNPs) entails the reduction and stabilization facilitated by functional groups of bacterial metabolites, including amino (–NH₂), carboxyl (–COOH), and hydroxyl (–OH), which play roles of reducing agents for transformation of silver ions (Ag⁺) into elemental metallic silver (Ag0). Free amino acids and their derivative peptides containing functional groups, such as carboxylates, amines, thiols, and phosphates, are capable of adsorbing onto the AgNP surface, thereby mitigating nanoparticle agglomeration through the formation of stabilizing surface layer.

Specific arrangements of amino acid residues within peptides possess the capability to affect the morphology and dimensions of silver nanoparticles (Alsamhary, 2020; Wypij, 2021). As in the present study the secondary metabolites characterized through LCMS analysis, exemplified by “1-{[7-(2-Amino-2-oxoethyl)-10-(3-amino-3-oxopropyl)-13-benzyl-16-(4-hydroxybenzyl)-6,9,12,15,18-pentaoxo-1,2-dithia-5,8,11,14,17-pentaazacycloicosan-4-yl] carbonyl} prolylarginylglycinamide” exhibit disulphide linkages, as well as linear and cyclic peptide side chains, which collectively possibly enhance antimicrobial efficacy alongside mechanisms that disrupt cellular integrity leading to cell death. Furthermore, these compounds serve as proton donors, given that a multitude of functional groups possess the potential to engage in redox reactions. The presence of the compound “Pentopyranosyl-(1 → 4)-6- deoxyhexopyranosyl-(1 → 2)-1-O -{(3beta,16alpha)-16-hydroxy-3-[(6-methylhexopyranuronosyl) oxy]-28-oxoolean-12-en-28-yl}pentopyranose” also contributes to antioxidant and anticancer activity, attributed to the existence of certain triterpenoids and oligosaccharides. This is accomplished through the induction of oxidative stress within cells, ultimately leading to apoptotic processes. In both aforementioned compounds, the presence of side chain atoms bearing –COOH, –C=O, and –OH terminal groups is conducive to the reduction of silver ions, facilitating the synthesis of nanoparticles. Additionally, there exist derivatives such as “(4R)-4-[(2S)-2-({2-[(1S)-1-amino-2-methylbutyl]-4,5-dihydro-1,3-thiazol-5-yl}formamido)-4-methylpentanamido]-4-{[(1S) -1-{[(3S,6R,9S,12R,15S,18R,21S)-18-(3-aminopropyl)-12-benzyl-15-(butan-2-yl)-3-(carbamoylmethyl)-6-(carboxymethyl)-9-(1H- imidazol -5-ylmethyl) -2,5,8,11,14,17,20-heptaoxo-1,4,7,10,13,16,19-heptaazacyclopentacosan-21-yl]carbamoyl}-2-methylbutyl]carbamoyl} butanoic acid,” efrotomycin, and tylvalosin; all of which contribute to the antimicrobial properties of the synthesized silver nanoparticles. The chemical characteristics of these identified compounds are possibly playing crucial roles in nanoparticle synthesis and tentatively determining their potential applications for antimicrobial activity, antibiotic removal, and anticancer activity (Dayma et al., 2024).

The application of the K. flava KKYHNGU1 strain for the biosynthesis of AgNPs elucidated the efficacy of the isolated bacterial strain as a viable biological and potential agent in nanoparticle fabrication. The observed alterations correspond with characteristic attributes associated with the formation of AgNPs. It is possible that due to secondary metabolites reported earlier, K. flava KKYHNGU1 possesses the capacity to reduce Ag⁺ ions to AgNPs. The discernible absorption peaks signify the occurrence of nanoparticles of varying sizes or morphologies, gives a sign of mixed composition. Such discrepancies may arise from a multitude of biochemical, biophysical factors influencing the bio-fabrication process and reduction rate of silver ions. In a similar vein, AgNPs have been manufactured utilizing various bacterial isolates and strains, as documented in several studies.

Critical insights into the functional groups implicated in the synthesis of AgNPs by K. flava KKYHNGU1 are elucidated through FTIR spectrum examination and analysis. The biochemical processes occurring during the bacteriogenic production of silver nanoparticles are characterized by the detected molecular vibrations (bending and stretching).

Some reactive groups, including hydroxyl, carbonyls, and sulfhydryl were identified and may play a significant role in the stabilization and reduction of silver nanoparticles. The detection of bending vibrations (C–H and C–O), which are indicative of presence of proteins, peptides and amino acid structures and their derivatives, further substantiates the involvement of proteins in the synthesis process. It is highly probable that these functional groups are derived from proteins and amino acids synthesized by bacterial species that participate in the reduction process. In a similar vein, You et al. (2024) noted that Fourier transform infrared (FTIR) spectroscopy revealed spectral bands within the range of 500–4,000 cm⁻¹. The stretching vibrations associated with alkanes (C–H), alcohols (O–H), primary amines (N–H), cyano (C–N), and carbonyl group (C–O) were recorded at 3,550 cm⁻¹, 3,062 cm⁻¹, 2,945 cm⁻¹, 2,358 cm⁻¹, 1,337 cm⁻¹, and 1,391 cm⁻¹, respectively. According to Al-Kherssani and Al-Mudhaffar (2024), ZV-AgNPs are synthesized utilizing Bacillus sp. The cultures from AW1-2 and their corresponding FTIR spectra demonstrated pronounced peaks at wavenumbers 3433.33 cm⁻¹, 2919.36 cm⁻¹, 2411.05 cm⁻¹, 1625.54 cm⁻¹, 1454.23 cm⁻¹, and 1128.56 cm⁻¹. The presence of a hydroxyl (O–H) group in alcohols is evidenced by the prominent peak observed at wavenumber 3433.33 cm⁻¹. Similarly, the vibration corresponding to the C–H group in alkanes is confirmed with the peak at 2919.36 cm⁻¹. The absorption bands observed at 2411.05 cm⁻¹, 1625.54 cm⁻¹, 1454.23 cm⁻¹, and 1128.56 cm⁻¹ can be attributed to the stretching vibrations of the C=O moiety, alkenes C=C moiety, the N–O stretching in nitro containing compounds, and the C–N moiety in amines, respectively (Al-Kherssani and Al-Mudhaffar, 2024).

The crystalline attributes of the bio-manufactured silver nanoparticles were corroborated through X-ray diffraction (XRD) analysis. The peaks manifesting in the diffraction pattern align with the crystallographic planes, thereby validating the crystalline properties of the material. Crystallite dimensions were derived from the assessment of peak positions, X-ray diffraction data, and full width at half maximum (FWHM), which collectively support the accurate sizing of nanoparticles. This observed crystallinity signifies the effective reduction and stabilization facilitated by K. flava KKYHNGU1. The uniformity in crystallite size suggests that the bacterial synthesis method employed is proficient in generating high-quality silver nanoparticles characterized by meticulously organized morphology and dimensions.

Peaks identified at 2θ angles of 37°, 44.8°, 64.9°, and 77° in the investigation conducted by Rajamanickam correspond to the crystallographic planes of 111, 200, 220, and 311, respectively (Govindaraj, 2025). As stated by Daniel et al. (2022), the angles of 2θ measured at 38.11°, 44.3°, 64.4°, and 77.3° correspond to Bragg’s reflections of the crystallographic orientations 111, 200, 220, and 311 correspondingly. The biogenic ZV-AgNPs were found to exhibit an average particle size of 27.31 nm (Govindaraj, 2025).

The scanning electron microscopy (SEM) analysis afforded a definitive representation of uniformly distributed spherical AgNPs. This morphological consistency is advantageous for a myriad of applications. The mean size of the nanoparticles was assessed at 96 nm, indicating enhanced reactivity due to an increased surface area. The evaluation of a 7 mm area at a 400 nm scale under high vacuum conditions set at 20 kV presents a remarkable opportunity for the investigation of the dispersion and morphology of the nanoparticles. The comprehensive analysis concluded that the applied synthesis methodology may yield nanoparticles exhibiting consistent dimensions and morphology. Energy-dispersive spectroscopy (EDS) analysis corroborated the purity of the bio-synthesized AgNPs, revealing a composition of 87.06% silver, 9.69% carbon, 3.25% oxygen, and a complete absence of measurable phosphorus. The highly concentrated silver content underscores the efficacy of the bio-synthesis protocol in producing AgNPs of elevated purity (Weber et al., 2025). The detected carbon and oxygen may originate from bacterial organic extracellular compounds, which could function as capping agents for the AgNPs, thereby enhancing the stability and functional characteristics of the nanoparticles (Jose et al., 2024). The absence of phosphorus implies minimal contamination, thereby reinforcing the purity and quality of the synthesized AgNPs. Consequently, the SEM and EDS analyses substantiate that the bacteriological bio-synthesis mechanism yields superior quality AgNPs distinguished by uniform spherical morphology, appropriate dimensions, and elevated purity standards. Concurrently, Paterlini et al. (2021) noted the observation of sphere-formed AgNPs at a 0.5 μm scale, showcasing sizes between 14 and 92 nm. Using SEM, researchers found that the AgNPs had dimensions ranging from 60 to 80 nm. Not long ago, Jose and colleagues achieved the successful creation of spherical AgNPs derived from Pseudomonas otitidis, which displayed an average diameter of 82.76 nm, as revealed by field emission scanning electron microscopy (Jose et al., 2024).

The study’s results indicate that Staphylococcus aureus presented the most considerable zone of inhibition, at 14 mm, suggesting its heightened responsiveness to the AgNPs at a level of 3 mg. This observation suggests that AgNPs possess the potential to effectively induce cellular death through their interaction with the bacterial cell membrane. Conversely, S. marcescens exhibited a diminished zone of growth inhibition at 10 mm, reflecting a reduced level of sensitivity. The lower antimicrobial activity observed against this Gram-negative bacterium may be ascribed to the makeup of its outer membrane and could additionally be connected to its ability to endure severe environmental circumstances, presenting another barrier to antibacterial initiatives. These bio-fabricated AgNPs have also shown promising results for the other two bacterial strains (E. coli and B. cereus) used to check antimicrobial potency. Ultimately, this investigation elucidated that AgNPs represent promising active bactericidal agents that exhibit efficacy against Gram-positive as well as Gram-negative bacteria, thereby underscoring their potential applications as broad spectrum antibacterial agent in the medical field. Moreover, the bactericidal potency of AgNPs against various bacterial isolates has been corroborated in several studies (Table 2).

A research investigation focusing on the remediation of trimethoprim utilizing AgNPs demonstrated marked enhancements in efficiency as the antibiotic concentrations diminished, achieving a reduction of 63.42% at 10 ppm, which signifies an effective interaction between trimethoprim and AgNPs, thereby harmonizing the presence of the antibiotic with the reactivity of the nanoparticles. A peak efficiency of 85.40% was attained at a concentration of 10 ppm, suggesting improved interaction due to the augmented availability of functional groups with functional and chemically active sites on the nanoparticles. The maximum absorbance observed at 270 nm confirmed the presence of TMP and exhibited a consistent decrease over time, thereby validating the efficacy of AgNPs in bioremediation of antibiotic. These results underscore the potential of AgNPs as effective agents for the remediation of trimethoprim in aqueous environments, highlighting the necessity to optimize concentration of this anthropogenic compound for effective treatment and reinforcing their important role in mitigating antibiotic contamination in soil and wastewater treatment contexts. Similarly, the study lead by Alishiri et al. (2023) documented 91.23–95.95% removal rate of the TMP antibiotic using magnetite-chitosan NPs at concentration of 22 mg/L. It is essential to point out that this research may be an innovative pursuit in leveraging silver nanoparticles (AgNPs) for extracting trimethoprim from wastewater.

A plethora of scholarly inquiries have been directed towards the evaluation of the anticancer and antitumor properties of silver nanoparticles, with numerous investigations yielding promising results across a wide spectrum of cellular models. The findings from Roy et al. (2024) reveal that silver nanoparticles (AgNPs) are marked by their diminutive size, generally situated in the nanometer spectrum, which aids their entry into malignant cells and nearby tissue. This diminutive scale enhances their ability to interact with cellular components and disrupt cellular processes. As AgNPs penetrate malignant cells, they can stimulate oxidative stress through the release of reactive oxygen species (ROS). The oxidative stress that results can inflict harm on cellular elements such as DNA, proteins, and lipids, ultimately resulting in cell death (apoptosis) (Gomes et al., 2021; Shaaban et al., 2024). This system leads to the activation of pro-apoptotic genes and concurrently blocks anti-apoptotic proteins, including BCL-2 (El-Naggar et al., 2024). These fundamental mechanisms necessitate further exploration, particularly concerning in vivo activity and therapeutic efficacy. Recent academic contributions have been summarized in Table 3. Moreover, an extensive appraisal of the IC50 value identified in this research (0.04 mg/mL) has been executed in tandem with ongoing research into the ramifications of AgNPs on assorted cell lines.

This study establishes Kocuria flava KKYHNGU1, isolated from rooftop solar panels, as a novel source for the green synthesis of silver nanoparticles with multifunctional activities. The work highlights the potential of extremophilic microbes from unexplored niches in advancing sustainable nanotechnology. While the results confirm antimicrobial, anticancer, and antibiotic-removal applications, limitations such as particle heterogeneity and incomplete mechanistic insights remain. Future research should focus on detailed physicochemical characterization, mechanistic validation of therapeutic effects, and evaluation of environmental safety to strengthen translational prospects. These directions will help transform solar panel microbiomes into a valuable platform for their biotechnological potential.