PGPR in Biofilm Formation and Antibiotic Production

Abstract

AbstractThe dynamic habitat existing around the plant root, the rhizosphere, is mainly inhabited by the bacteria and is collectively termed as plant growth-promoting rhizobacteria (PGPR). They play an important role in protecting the crops, improvement in the health of the soil, and promotion of plant growth. The dominant members of PGPR are the biofilm-producing bacteria, which synthesize a wide spectrum of multifunctional polysaccharides. Bacterial species like Pseudomonas, Bacillus, Azospirillum, Rhizobium, and Serratia assist in biofilm formation that contribute in sustained agricultural growth by acting as “biofilmed biofertilizers.” Some exopolysaccharide can bind with sodium ions to impart protection from salinity stress. PGPR biofilm is also beneficial for biocontrol of diseases and enhancing nutrient availability to plants. Antibiotics, synthesized by PGPR, are found effective against Gram-positive and Gram-negative bacteria and also against pathogenic fungi. Some noteworthy antibiotics include phenazine-1-carboxyclic acid, oomycin, zwittermicin A, 2,4-diacetylphloroglucinol, kanosamine, pyoluteorin, pyrrolnitrin, and pantocin. The syntheses of antibiotics by PGPR are regulated by cascade of endogenous signals such as N-acyl homoserine lactones and sigma factors and are upregulated by highly conserved sequences of genes. The antibiotics belonging to the group of polyketides, lipopeptides, and heterocyclic nitrogenous compounds have efficacy against wide range of plant pathogens that has inhibitory effect to the plant growth. This chapter will focus on biofilm formation and biosynthesis of antibiotics by PGPR and their effective applications.KeywordsAntibiotics Bacillus BiofilmPGPRPseudomonads