Poly-γ-glutamic acid secretion protects Bacillus subtilis from zinc and copper intoxication

Abstract

Zinc and copper are essential micronutrients that serve as a cofactors for numerous enzymes. However, when present at elevated concentrations, zinc and copper are highly toxic to bacteria. To combat the effects of zinc and copper excess, bacteria have evolved a wide array of defense mechanisms. Here, we show that the Gram positive soil bacterium, Bacillus subtilis, produces the extracellular polymeric substance, poly-gamma-glutamate ({gamma}-PGA) as a protective mechanism in response to zinc and copper excess. Furthermore, we provide evidence that zinc and copper dependent {gamma}-PGA production is independent of the DegS-DegQ two component regulatory system and likely occurs at a post-transcriptional level. These data provide new insight into bacterial metal resistance mechanisms and contribute to our understanding of the regulation of bacterial {gamma}-PGA biosynthesis. ImportanceZinc and copper are potent antimicrobial compounds. As such, bacteria have evolved a diverse range of tools to prevent metal intoxication. Here, we show that the Gram-positive model organism, Bacillus subtilis, produces poly-gamma-glutamic acid ({gamma}-PGA) as a protective mechanism against zinc and copper intoxication and that zinc and copper dependent {gamma}-PGA production occurs by a yet undefined mechanism independent of known {gamma}-PGA regulation pathways.