Cross-species activation of hydrogen cyanide production by a promiscuous quorum-sensing receptor promotes Chromobacterium subtsugae competition in a dual-species model

Abstract

Many saprophytic bacteria have LuxR-I-type acyl-homoserine lactone (AHL) quorum-sensing systems that may be important for competing with other bacteria in complex soil communities. LuxR AHL receptors specifically interact with cognate AHLs to cause changes in expression of target genes. Some LuxR-type AHL receptors have relaxed specificity and are responsive to non-cognate AHLs. These promiscuous receptors might be used to sense and respond to AHLs produced by other bacteria by eavesdropping. We are interested in understanding the role of eavesdropping during interspecies competition. The soil saprophyte Chromobacterium subtsugae has a single AHL circuit, CviR-I, 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 have utilized a coculture model with C. subtsugae and another soil saprophyte, Burkholderia thailandensis . Using this model, we previously showed that promiscuous activation of CviR by B. thailandensis AHLs provides a competitive advantage to C. subtsugae . Here, we show that B. thailandensis AHLs activate transcription of dozens of genes in C. subtsugae, including the hcnABC genes coding for production of hydrogen cyanide. We show that hydrogen cyanide production is population density-dependent and demonstrate that the cross-induction of hydrogen cyanide by B. thailandensis AHLs provides a competitive advantage to C. subtsugae . Our results provide new information on C. subtsugae quorum sensing and are the basis for future studies aimed at understanding the role of eavesdropping in interspecies competition.

Increased environmental microbial diversity reduces the disease risk of a mosquitocidal pathogen

“…Some Chromobacterium have further been shown to use promiscuous, cross-species quorum sensing (QS) to control the production of virulence factors that kill competitors ( 65 ). A simplified dual-species assay shows QS controls the density-dependent production of cyanide and antibiotics by C. subtsugae with the former being the primary factor that enables it to outcompete other saprophytes ( 66 , 67 ). In turn, QS-deficient mutants of C. violaceum produce less cyanide ( 68 ), while cyanide produced by other Chromobacterium spp.…”

Regulation of an antibiotic resistance efflux pump by quorum sensing and a TetR-family repressor inChromobacterium subtsugae

“…The cdeR expression plasmid pQE30 cdeR was made by amplifying the cdeR gene with primer-incorporated BamHI and HindIII restriction enzyme sites, digesting with BamHI/HindIII and ligating to BamHI/HindIII-digested pQE30 (Qiagen). CV017 ΔcviI CV017 with an in frame, unmarked cviI deletion [16] CV017 ΔcviR CV017 with an in frame, unmarked cviR deletion [16] CV017 ΔcdeR CV017 with an in frame, unmarked cdeR deletion [11] CV017 Transcription reporter assays. To assess activation of the cdeA promoter in recombinant E. coli, we used E. coli strain DH5a carrying cviR downstream of the lac promoter in pBBRMCS-5…”

“…CviI synthesizes N- hexanoyl homoserine lactone (C6-HSL), and C6-HSL-bound CviR binds to a canonical lux- box-like sequence in the promoter of target genes [8]. Activation of the CviR-I system induces expression of dozens of genes [9]. Many of the CviR-I-responsive genes have roles that are predicted or known to be important for competing with other bacteria, for example by activating the production of the purple-pigmented antibiotic violacein [7] and hydrogen cyanide [9].…”

“…Activation of the CviR-I system induces expression of dozens of genes [9]. Many of the CviR-I-responsive genes have roles that are predicted or known to be important for competing with other bacteria, for example by activating the production of the purple-pigmented antibiotic violacein [7] and hydrogen cyanide [9].…”