Identifying more targeted antimicrobials active against selected bacterial phytopathogens.

Abstract

Phytopathogens are a global threat to the world's food supply. The use of broad-spectrum bactericides and antibiotics to limit or eliminate bacterial infections is becoming less effective as levels of resistance increase, while concurrently becoming less desirable from an ecological perspective due to their collateral damage to beneficial members of plant and soil microbiomes. Bacteria produce numerous antimicrobials in addition to antibiotics, such as bacteriocins with their relatively narrow activity spectra, and inhibitory metabolic by-products, such as organic acids. There is an interest in developing these naturally occurring antimicrobials for use as alternatives or supplements to antibiotics. In this study, we investigate the inhibitory potential of 217 plant-associated bacterial isolates from 44 species including plant pathogens, plant growth promoting rhizobacteria and plant commensals. Over half of the isolates were found to produce antimicrobial substances, of which 68% were active against phytopathogens. Even more intriguing, 98% of phytopathogenic strains were sensitive to the compounds produced specifically by plant growth promoting rhizobacteria. These data argue that plant-associated bacteria produce a broad range of antimicrobial substances, and that the substances produced preferentially target phytopathogenic bacteria. There is a need for novel antimicrobials for use in agriculture. The methods presented here reveal the potential for simple phenotypic screening methods to provide a broad range of potential drug candidates.