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 andgrowth hormone such as indole acetic acid (AIA). These bacteria can also slow the growth of plant pathogensthrough the production of several antimicrobial metabolites. To investigate the role of rhizobacteria as abiostimulant 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 ofidentification (physiological and biochemical tests), B8 was identified by 16S rRNA gene sequencing as Bacillusclausii. The ability of the strain to produce lytic enzymes such as cellulases, chitinases, pectinases, andphospholipases was studied. Furthermore, the strain B8 was tested for the capability to produce plant growthmetabolites like phosphatases and phytases in order to solubilize inorganic phosphate and production ofsiderophores, 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 experimentsindicated 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. Thevegetative growth parameters; Roots length, lateral roots number, stem length, number of leaves, diameters ofstems and plant weight were significantly improved. We also noted capacity of bacteria to colonize root systemsof both plants B. napus and M. sativa in one week of inoculation. The overall results of this study showed thatB clausii B8 has a great potential to be commercialized as a biostimulant agent and provide promising newoption for sustainable agriculture