Cyanide Production by Prey Bacteria Protects Them against Predation by Bdellovibrio bacteriovorus

Abstract

Backgrounds: Bdellovibrio bacteriovorus is obligate predatory bacterium which is prey upon numerous gram-negative bacteria and ubiquitous in terrestrial and aquatic environments Objectives: Co-existence of prey and predator is wide spread among bacterial feeding microorganisms include B. bacteriovorus. Predation by B. bacteriovorus gives impact on structure of bacterial communities and many bacteria have evolved defense mechanism against predation. In this study, we show that extracellular secondary metabolite produced by the soil bacterium Chromobacterium piscinae functions as a defense strategy against predatory bacteria Methods: We found that C. piscinae is not predated by B. bacteriovorus when cultivated in Dilute Nutrient Broth (DNB). However, C. piscinae can be predated on within a nutrient-free buffer, HEPES. We examined that spent-DNB media of C. piscinae significantly delays predation of E. coli MG1655 by B. bacteriovorus. We identified that hydrogen cyanide (HCN) is major inhibitory metabolite of C. piscinae spent-media by removing cyanide with purging and scavenging with Vitamin B12a. The concentration of cyanide of DNB spent-media is about 110uM, we examined that it show same level of inhibitory effect with KCN 110uM solution. Conclusions: The results suggest that bacterial secondary metabolites, hydrogen cyanide, responsible for the inhibition of B. bacteriovorus predation and thus likely contribute to protect prey against predation.