Abstract
Recently, crop management has involved excessive use of chemical fertilizers and pesticides, compromising public health and environmental integrity. Rhizobacteria, which can enhance plant growth and protect plants from phytopathogen, are eco-friendly and have been attracting increasing attention. In the current study, Bacillus subtilis RS10 isolated from the rhizosphere region of Cynodon dactylon, inhibited the growth of indicator strains and exhibited in vitro plant growth-promoting traits. A whole-genome analysis identified numerous biosynthetic gene clusters encoding antibacterial and antifungal metabolites including bacillibactin, bogorol A, fengycin, bacteriocin, type III polyketides (PKs), and bacilysin. The plant growth-promoting conferring genes involved in nitrogen metabolism, phosphate solubilization, hydrogen sulfide, phytohormones, siderophore biosynthesis, chemotaxis and motility, plant root colonization, lytic enzymes, and biofilm formation were determined. Furthermore, genes associated with abiotic stresses such as high salinity and osmotic stress were identified. A comparative genome analysis indicated open pan-genome and the strain was identified as a novel sequence type (ST-176). In addition, several horizontal gene transfer events were found which putatively play a vital role in the evolution and new functionalities of a strain. In conclusion, the current study demonstrates the potential of RS10 antagonism against important pathogens and plant growth promotion, highlighting its application in sustainable agriculture.
Highlights
Bacterial strains that efficiently colonize plant roots and promote plant growth by direct or indirect mechanisms are known as plant growth-promoting bacteria (PGPB) [1].The direct mechanism includes stimulation of root growth and biofertilization, while the indirect mechanism involves biological control comprised of induction of systemic resistance and production of antimicrobial metabolites [2]
According to their biosynthetic pathways, these antimicrobial metabolites can be divided into three main classes: nonribosomal peptides (NRPs), polyketides (PKs), and ribosomally synthesized post-translationally modified peptides (RiPPs) [5]
The dry extract was dissolved in phosphate buffer solution (250 mg/mL) and antibacterial activity was determined against a set of American Type Culture Collection (ATCC) bacterial strains via agar well diffusion assay and zones of inhibitions (ZOI) were measured in mm [15]
Summary
The direct mechanism includes stimulation of root growth and biofertilization, while the indirect mechanism involves biological control comprised of induction of systemic resistance and production of antimicrobial metabolites [2]. Antimicrobial metabolites produced by Bacillus spp. are extremely diverse [4]. According to their biosynthetic pathways, these antimicrobial metabolites can be divided into three main classes: nonribosomal peptides (NRPs), polyketides (PKs), and ribosomally synthesized post-translationally modified peptides (RiPPs) [5]. NRPs such as surfactin and fengycin are synthesized by mega enzymes called nonribosomal peptide synthetases (NRPSs). PKs include bacillaene and difficidin is another class of antimicrobial metabolites synthesized by polyketide synthetases (PKSs).
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