Molecular characterization of Bacillus subtilis OKR isolated from wheat rhizosphere reveals key outer membrane proteins associated with plant growth promotion: A step towards climate-smart agriculture

Abstract

Bacillus subtilis, is reported to be an efficient bacterium and a universal cell factory for industry, medicine and biomaterials. It also possesses plant growth promotional activities. In the current study, we aimed to identify and characterize wheat rhizosphere B. subtilis at molecular level such as by 16S RNA gene, in vitro screening, and outer membrane proteins using host mimic simulation by two-dimensional gel electrophoresis. Based on 16S RNA gene results, the isolate OKR was identified as B. subtilis and clustered with Bacillus subtilis strain QD517 and B. subtilis strain LQ20. The isolate assigned the name as B. subtilis strain OKR under accession no. KP201140.1. In vitro screening of OKR for growth proportional and biocontrol activities has revealed it as an effective type of plant growth rhizobacterium. Furthermore, the outer membrane protein analysis not only substantiated the attributes of B. subtilis strain OKR as PGPR, but also revealed that leaf extract (LE) media could be used as an alternative in vivo model for plants to characterize plant promotional activities at molecular level. Each condition was found to correspond to a unique protein expression profile due to the significant protein’s expression diversity observed between the control and the simulated host condition. Two-component response regulators and heat shock proteins are key proteins identified under host-mimicking conditions that appear to be indispensable for plant growth-promoting activities. Furthermore, the identification of common proteins such as Na⁺/H⁺ antiporters and ABC transporter-like proteins holds a promise for survival and metabolic activity in each niche. We believe that our findings will contribute to the development of environment-friendly, sustainable, and climate-smart agricultural technology strategies that can succeed under limited environmental conditions.