Antimicrobial lipopeptides of bacillus: Natural weapons for biocontrol of plant pathogens

Abstract

Bacillus species are ubiquitous bacteria in agricultural soils and possess many traits that make them well suited as biocontrol agents of various soil borne pathogens. They are aerobic, Gram-positive bacteria with remarkable ability to produce highly resistant endospores and are well adapted to grow in the rhizosphere. Until today, hundreds of strains of genus Bacillus, including Brevibacillus and Paenibacillus, have been identified that produce a variety of antimicrobial substances, e.g., antibiotics. Bacillus subtilis, a model organism of this group is known to produce over two dozen molecules with antibiotic properties and an amazing variety of structures. Lipopeptides are the most frequent antibiotic compounds produced by bacilli exhibiting antibacterial and/or antifungal actions against a spectrum of pathogenic bacteria and fungi with surfactant activities in exceptional cases. Among these, cyclic lipopeptides (LPs) of the surfactin, iturin and fengycin families have well known potential in biotechnology and bio-pharmaceutical applications. Structurally, these amphiphilic molecules share a common cyclic structure comprised of a β-amino or β-hydroxy fatty acid integrated into a peptide moiety and have been classified based on the difference in amino acid sequences and fatty acid branching. Besides, lipopeptides have also been reported to contribute to the ecological fitness of the producing strain thus helping them to adapt to their ecological niche. Numerous reports covering in vitro production of antibiotic molecules from different Bacillus spp. are available however the number reduces dramatically only to few wherein production and/or recovery of these molecules could be demonstrated successfully under natural or greenhouse conditions. The aim of this review is to summarize the recent findings of Bacillus lipopeptides with antibiotic properties, regulatory pathways involving their production and their role in the ecological fitness of Bacillus.