Poster Session - Abstract # 28

Competitive Impact of Hydrogen Cyanide Produced via Acyl-homoserine Lactone-dependent Eavesdropping by Chromobacterium subtsugae

Nathan Smith, Cheyenne Loo, Anna Oller, Pratik Koirala, Isabelle Parisi, Josephine Chandler

Department of Molecular Biosciences, The University of Kansas, Lawrence, KS, USA

Many soil saprophytic bacteria use LuxR-I-type acyl-homoserine lactone (AHL) quorum-sensing systems to activate production of antimicrobials that can be utilized to compete with other bacteria in polymicrobial communities.  LuxR signal receptors specifically interact with cognate AHLs produced through LuxI to cause changes in gene expression.  Some LuxR-type AHL receptors have relaxed specificity and are responsive to non-cognate AHLs.  The soil saprophyte Chromobacterium subtsugae has a single AHL circuit, CviI-R, which produces and responds to N-hexanoyl-HSL (C6-HSL).  The AHL receptor CviR can respond to a variety of AHLs in addition to C6-HSL.  In prior studies, we showed that CviR allows C. subtsugae to compete with another saprophyte, Burkholderia thailandenis, by responding to B. thailandensis AHLs by eavesdropping.  In this study, we used RNAseq to show that eavesdropping activates production of hydrogen cyanide (HCN).  We showed that C. subtsugae produces 2,200-3,600 μM cyanide (CN^-) in C. subtsugae pure cultures after 12 hours, which is dependent on both the cyanide biosynthetic genes and the quorum-sensing receptor CviR.  We also show that potassium cyanide can inhibit growth of B. thailandensis at a half-maximal concentration (IC₅₀) of 114 μM.  We also used genetic mutants to demonstrate that hydrogen cyanide is needed for C. subtsugae to compete with B. thailandensis in response to B. thailandensis AHLs in laboratory cocultures.  Our results demonstrate that C. subtsugae uses hydrogen cyanide for interspecies competition in response to non-native AHLs via eavesdropping and establish a laboratory coculture system that can be used for future studies on the role of eavesdropping in interspecies competition.

Important words: hydrogen cyanide, eavesdropping, quorum sensing