Exploring biofertilizer potential of plant growth-promoting rhizobacteria Bacillus clausii strain B8 (MT305787) on Brassica napus and Medicago sativa

Abstract

Plant Growth Promoting Rhizobacteria (PGPR) are soil bacteria that can stimulate plant growth by supplying substances that are usually in limited quantities in the soil especially phosphorous, nitrogen and growth hormone such as indole acetic acid (AIA). These bacteria can also slow the growth of plant pathogens through the production of several antimicrobial metabolites. To investigate the role of rhizobacteria as a biostimulant agent a novel bacterium B8, isolated from the rhizospheric soil of medlar (Mespilus germanica L.- Family Rosaceae), was evaluated on Brassica napus and Medicago sativa. In addition to the classical methods of identification (physiological and biochemical tests), B8 was identified by 16S rRNA gene sequencing as Bacillus clausii. The ability of the strain to produce lytic enzymes such as cellulases, chitinases, pectinases, and phospholipases was studied.  Furthermore, the strain B8 was tested for the capability to produce plant growth metabolites like phosphatases and phytases in order to solubilize inorganic phosphate and production of siderophores, cyanhydric acid (HCN) and indole-3-acetic acid. The strain was able to produce lytic enzymes, with an intense production of siderophores and to solubilize inorganic phosphate. Result of in vivo experiments indicated that the application of B8 at 107 CFU/mL, improved markedly the germination rate of rapeseed, whereas alfalfa seeds treated with the same strain showed a lower germination rate than the controls. The vegetative growth parameters; Roots length, lateral roots number, stem length, number of leaves, diameters of stems and plant weight were significantly improved. We also noted capacity of bacteria to colonize root systems of both plants B. napus and M. sativa in one week of inoculation.  The overall results of this study showed that B clausii B8 has a great potential to be commercialized as a biostimulant agent and provide promising new option for sustainable agriculture.