Richa Raghuwanshi

This review analyses the growing field of microbial metabolites in agriculture, moving beyond the widespread narratives to evaluate the scientific foundations, efficacy claims, and ecological implications of their widespread application. This article discusses the widespread benefits of using microbial metabolites in agriculture to enhance plant physiology, biochemistry, and defense. The biocontrol agents protect crops through direct and indirect mechanisms, including direct antagonism, resource competition, and niche exclusion at root infection sites. Furthermore, they also activate innate plant immunity via Induced Systemic Resistance (ISR) and Systemic Acquired Resistance (SAR). By recognizing Pathogen-Associated Molecular Patterns (PAMPs), these metabolites trigger defense hormones such as salicylic acid, jasmonic acid, and ethylene and also prompt the synthesis of defense proteins. While live microbes are sensitive to environmental shifts, the benefits of isolating their pure metabolites and formulating biopesticides help standardize doses and offer extended shelf lives. While microbial metabolites offer a “green” alternative to synthetic agrochemicals, the current research landscape is often characterized by reductionist “single-strain, single-metabolite” approaches and a significant lack of comprehensive environmental impact studies. Here, we have also discussed progress in metabolite discovery through omics technologies, re-evaluated the often-overstated efficacy of these compounds in plant growth and defense, and assessed the ecological consequences, including soil microbiome disruption and associated risks such as horizontal gene transfer. We propose a framework for (i) efficacy validation across environments, (ii) ecological risk assessment endpoints, and (iii) regulatory monitoring priorities and ethically guided precision agricultural solutions to fully harness the potential of microbial metabolites for a sustainable future.

Micronutrient deficiencies have significant impacts on plant growth, grain yield and nutritional quality. Biofortification through seed biopriming can be an effective strategy in meeting the challenges of malnutrition under the changing climatic conditions. Therefore, to evaluate the effects of potent growth promoting rhizospheric microbes Enterobacter cloacae BHUSR1, Serratia marcescens BHUSR2 and Klebsiella aerogenes BHUSR3 on nutrient content of oat grains at different irrigation levels (7 and 10 days) the present work was undertaken. The experiments were conducted in field trials in a randomized complete block design, and the data were statistically analyzed using analysis of variance (ANOVA). The yield was improved significantly upto 93% after seed biopriming even when grown under drought. Improvement in macronutrients observed was upto 39.4% for potassium, 51.1% for phosphorus, while the essential micro-nutrients augmented were 50.5% zinc and 41.6% manganese. Among all the selected strains Klebsiella aerogenes BHUSR3 was found to be most effective in mobilizing phosphorous, potassium, iron, zinc, manganese under irrigated conditions. The macro and micro-nutrients biofortified under drought were bacterial dependent with no common trend observed.

In natural ecosystems, most of the micronutrients are present in forms that are inaccessible to plants or bound in organic molecules. The assimilation of nutrients by plants is assisted by millions of soil microbes that possess the ability to depolymerize or mineralize nutrients into an available form to plants. A deficiency in micronutrients can disrupt the morphological and physiological growth of plants. Accessibility to both micro and macro nutrients by utilizing microorganisms has emerged as an excellent strategy in sustainable agriculture. Microbes found in the soil-root interface have the potential to solubilize the trace element. The abundant proliferation of Plant Growth-Promoting Microorganisms (PGPMs) in the rhizosphere is advantageous for plants, as these microorganisms are widely acknowledged for their growth-promoting activities. Nevertheless, there is still a considerable amount to discover regarding the physiology and mechanisms governing the absorption, translocation, and deposition of plant micronutrients facilitated by rhizobacteria. Microbes enhance plant growth by altering hormonal signaling, inhibiting pathogens, or increasing nutrient bioavailability. Application of microbial inoculants to plants at an early stage of development enhances their performances even under stress conditions. PGPM has come up as a reliable alternative to replace the chemicals in agricultural sectors as an environment cleanup strategy. This review highlights the role of soil microbes and their mechanisms they adopt in plant nutrient mobilization and uptake.

Endophytic bacteria reside asymptomatically inside host plant tissues and have the potential to protect the host plant from phytopathogens and enhance plant immunity. Exploration of the biocontrol mechanism of these beneficial bacteria can assure the development of eco-friendly pesticides for the effective management of phytopathogens. In our study, the isolated endophytic bacteria examined for its antimicrobial potential was identified as Pseudomonas gessardii strain RRBHU-1 based on 16 S rRNA gene sequence analysis. The crude extract containing the secondary metabolites from the P. gessardii strain RRBHU-1 demonstrated antagonistic activity against Xanthomonas vesicatoria, the causal organism of bacterial leaf spot disease in tomato plants. X. vesicatoria when treated with the RRBHU-1 extract showed disruption of the cell membrane, significant ROS production, and substantial antibiofilm activity. The extract separated through TLC and RP-HPLC and characterized using FT-IR, NMR, and HRAMS, and was identified as 4-Dodecylbenzene sulfonic acid (4-DBSA). This study is the first report on the presence of 4-DBSA in the Pseudomonas genera. In silico studies revealed stable interactions and high binding energies of 4-DBSA and the proteins directly involved in Xanthomonas virulence. This study suggests the possible utilization of P. gessardii strain RRBHU-1 as biopesticides against X. vesicatoria, encompassing sustainable agricultural practices.

The organic compounds 2-aminopyrimidine (AP) and 4-aminobenzoic acid (PABA) were selected for the synthesis of a compound by establishing the phase diagram and adopting the solid-state synthesis method. The phase diagram analysis suggested the formation of a novel intermolecular compound (IMC) at a 1:1 stoichiometric ratio of AP and PABA, along with two eutectics at 0.25 and 0.90 mole fractions of AP. FTIR and NMR spectroscopy were used for the structure elucidation of the intermolecular compound. The powder X-ray diffraction analysis revealed the novel nature of IMC (APPABA) and the mechanical mixture nature of eutectics. The sharp and single peak of the DSC curve suggested the melting and pure nature of the synthesized IMC. Various thermodynamic parameters of IMC and eutectics were studied. A single crystal of the IMC was grown from solution and its single-crystal X-ray diffraction analysis revealed that it crystallized in a monoclinic system with the P21/n space group. Hirshfeld surface analysis further validated the weak non-covalent interactions summarized through the single-crystal X-ray analysis. Studies on the IMC were thoroughly conducted to evaluate its antibacterial activity with reference to antibiotics, and it showed significant positive responses against various pathogenic microbial isolates (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella aerogenes, and Shigella boydii) and non-pathogenic microbial isolates (Enterobacter cloacae, Pseudomonas azotoformans, and Burkholderia paludis). It was also found effective against methicillin-resistant bacterial strains viz. Staphylococcus aureus MRSA.

The organic compounds, 2-aminopyrimidine (AP) and 4-aminobenzoic acid (PABA), are selected for the synthesis of a compound by establishing the phase diagram adopting the solid-state synthesis method. Phase diagram study infers the formation of a novel intermolecular compound (IMC) at 1:1 stoichiometric ratio of AP and PABA along with two eutectics at 0.25 and 0.90 mole fractions of AP. The FTIR and NMR spectroscopy are studied for structure elucidation of intermolecular compound. Powder X-ray diffraction study reveals the novel nature of IMC (APPABA) and the mechanical mixture nature of eutectics. Sharp and single peak of the DSC curve suggests the melting and pure nature of the synthesised IMC. Various thermodynamic parameters of IMC and eutectics have been studied. The single crystal of IMC has grown from solution and its single crystal X-ray diffraction analysis reveals that IMC has crystallised in a monoclinic having P21/n space group. Hirshfeld surface analysis further validated the weak non-covalent interactions summarized through single crystal X-ray study. Studies on IMC thoroughly have been done for its antibacterial activity and it has shown significant positive responses against various pathogenic microbial isolates (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella aeruginosa, Shigella boydii) and non-pathogenic microbial isolates (Enterobacter cloacae, Pseudomonas azotoformans). It was also found effective against methicillin-resistant bacterial strains viz. Staphylococcus aureus MRSA. The biodegradable IMC is an effective functional material with its future applicability as an antibacterial agent extending up to drug-resistant bacterial strains.