The principal mechanisms of growth promotion include production
of growth stimulating phytohormones, solubilization and mobilization of phosphate,
siderophore production, antibiosis, i.e., production of antibiotics, inhibition
of plant ethylene synthesis, and induction of plant systemic resistance to
pathogens. It is very likely that plant growth promotion by rhizosphere bacilli
may be a result of combined action of two or more of these mechanisms