Potentiality of Biosurfactant Producing Microbes in Plant Growth Promotion and Inhibition of Phytopathogenic Fungi

Abstract

Plants are colonized by a huge number of microbial populations than can even over cede the total number of plant cells. The microorganisms dwelling in the plant rhizosphere form a diverse array of interactions with the host plants. These groups of microorganisms are known for their active role in boosting plant growth by nutrient recycling or protecting the plants from different biotic and abiotic stresses through the production of different metabolites. The sustainability and effectiveness of the plant-associated microorganisms still lack the exploration of novel rhizosphere microbial species and hence need further understanding. This thesis was designed to study the potency of novel soil microorganisms to replace synthetic agricultural inputs. The initial research was focused on isolating unique and highly potent biosurfactant (BS) producing bacterial isolates from the rhizosphere of several seasonal leguminous and non-leguminous crop plants as well as non-crop plants. Subsequently, a potent BS producer was selected among the 25 rhizosphere bacterial isolates and it was identified to be Bacillus altitudinis MS16 using physiological, biochemical, and molecular analyses. The BS was extracted by acid precipitation followed by solvent extraction and purified by silica gel column chromatography. The FTIR, HP-LC and LC-ESI-MS analyses, identified and confirmed the BS to be a lipopeptide consisting of two bioactive compounds surfactin and iturin A. The BS demonstrated outstanding stability across a variety of environmental factors and was found to be non-toxic against human red blood cells (RBCs), indicating its broad range of use. The most efficient BS producer B. altitudinis MS16 was evaluated for its direct and indirect plant growth promoting (PGP) traits and it was found to fix 82.80 ± 0.6 and#956;g N mg-1 of carbon, 4.4 and#956;mol ml-1 of ammonia, can produce 40.74 ± 0.7 and#956;g ml-1 of IAA, can solubilize 7.72 ± 0.9 and#956;g ml-1 of insoluble phosphorus and secrete various hydrolytic enzymes. In addition to solubilizing potass