Bacillus and Paenibacillus spp.: Potential PGPR for Sustainable Agriculture

Abstract

The Gram-positive aerobic endospore-forming bacteria (AEFB) belonging to the genus Bacillus and Paenibacillus are essentially ubiquitous and occur abundantly in most rhizospheric soils. In the rhizosphere, species of these two genera are involved in atmospheric nitrogen fixation, solubilization of soil phosphorus and uptake of micronutrients, and production of phytohormones and antimicrobial metabolites. Multiple species of Bacillus and Paenibacillus affect the crop growth and its health by three different ecological mechanisms viz, promotion of host plant nutrition and growth, antagonism against fungal, bacterial, nematode pathogens and insect pests, and stimulation of host defence mechanisms. Specific strains of both Bacillus and Paenibacillus spp. are known to elicit induced systemic resistance (ISR) similar to that of Pseudomonas spp. which leads to the stimulation of host defence mechanisms against multiple pathogens on diverse crop plants. Several species of Bacillus and Paenibacillus are the major source of broad spectrum peptide antibiotics that are active against various microbial and nematode pathogens. Endophytic colonization and biofilm formation by these two genera are also reported. These plant growth promoting abilities of Bacillus and Paenibacillus can make them suitable plant growth promoting rhizobacteria for their application in sustainable agriculture.