Vibrio campbellii DS40M4 is a tractable model strain that diverges from the canonical quorum-sensing regulatory circuit in vibrios

BB120 (previously designated as ) is a fundamental model strain for studying population density-based cell-to-cell communication, known as quorum sensing. In BB120, sensing of autoinducers at high cell densities activates the expression of the master transcriptional regulator, LuxR, which controls the expression of genes involved in group behaviors. The environmental isolate DS40M4 was recently shown to be capable of natural transformation, a process by which bacteria take up exogenous DNA and incorporate it into their genome via homologous recombination. In contrast, BB120 is not naturally transformable. Here, we compare additional phenotypes between these two strains. DS40M4 has a faster growth rate and stronger type VI secretion-mediated cell killing, whereas BB120 forms more robust biofilms and is bioluminescent. To explore the function of DS40M4-encoded homologs of the BB120 quorum-sensing system, we exploited the power of natural transformation to rapidly generate >30 mutant strains. Our results show that DS40M4 has a similar quorum-sensing circuit to BB120 but with three distinct differences: 1) DS40M4 lacks the canonical HAI-1 autoinducer LuxM synthase but has an active LuxN receptor, 2) the quorum regulatory small RNAs (Qrrs) are not solely regulated by autoinducer signaling through the response regulator LuxO, and 3) the DS40M4 LuxR regulon is <100 genes, which is relatively small compared to the >400 genes regulated in BB120. This work illustrates that DS40M4 is a tractable and relevant model strain for studying quorum-sensing phenotypes in .