Abstract
Vibrio cholerae, the causative agent of cholera, is a model organism for studying virulence regulation, biofilm formation, horizontal gene transfer, and the cell-to-cell communication known as quorum sensing (QS). As in any research field, discrepancies between data from diverse laboratories are sometimes observed for V.cholerae. Such discrepancies are often caused by the use of diverse patient or environmental isolates. In this study, we investigated the inability of a few laboratories to reproduce high levels of natural transformation, a mode of horizontal gene transfer that is specifically induced on chitinous surfaces. This irreproducibility was mostly related to one specific isolate of V.cholerae: the O1 El Tor C6706 strain. C6706 was previously described as QS proficient, an important prerequisite for the induction of natural competence for transformation. To elucidate the underlying problem, we collected seven isolates of the same C6706 strain from different research laboratories in North America and Europe and compared their phenotypes. Importantly, we observed a split response with respect to QS-related gene expression, including chitin-induced natural competence and type VI secretion (T6S). While approximately half of the strains behaved as reported for several other O1 El Tor pandemic isolates that are commonly studied in the laboratory, the other half were significantly impaired in QS-related expression patterns. This impairment was caused by a mutation in a QS-related gene (luxO). We conclude that the circulation of such QS-impaired wild-type strains is responsible for masking several important phenotypes of V.cholerae, including natural competence for transformation and T6S. IMPORTANCE Phenotypic diversity between laboratory-domesticated bacterial strains is a common problem and often results in the failed reproduction of published data. However, researchers rarely compare such strains to elucidate the underlying mutation(s). In this study, we tested one of the best-studied V.cholerae isolates, O1 El Tor strain C6706 (a patient isolate from Peru), with respect to two main phenotypes: natural competence for transformation and type VI secretion. We recently demonstrated that the two phenotypes are coregulated and specifically induced upon the growth of pandemic V.cholerae O1 El Tor strains on chitinous surfaces. We provide evidence that of seven C6706 strains collected from different laboratories, four were impaired in the tested phenotypes due to a mutation in a QS gene. Collectively, our data indicate that the circulation of such a mutated wild-type strain of C6706 might have had important consequences for QS-related data.
Highlights
Vibrio cholerae, the causative agent of cholera, is a model organism for studying virulence regulation, biofilm formation, horizontal gene transfer, and the cell-to-cell communication known as quorum sensing (QS)
We recently demonstrated that the two phenotypes are coregulated and induced upon the growth of pandemic V. cholerae O1 El Tor strains on chitinous surfaces
We recently showed that the T6SS of several pandemic V. cholerae O1 El Tor isolates is induced upon growth on chitin [8], which is one of the primary niches of the pathogen in its natural aquatic habitat [9]
Summary
The causative agent of cholera, is a model organism for studying virulence regulation, biofilm formation, horizontal gene transfer, and the cell-to-cell communication known as quorum sensing (QS). We investigated the inability of a few laboratories to reproduce high levels of natural transformation, a mode of horizontal gene transfer that is induced on chitinous surfaces This irreproducibility was mostly related to one specific isolate of V. cholerae: the O1 El Tor C6706 strain. TfoX alone is not sufficient to allow DNA uptake to occur, as the induction of the second part of the DNA-uptake machinery (e.g., the protein ComEA, which pulls the DNA into the periplasm [16, 17], and the inner membrane transporter ComEC [15]) requires additional input from the quorum-sensing (QS) circuitry [18] (Fig. 1) This input occurs via the master regulator of QS, HapR, which itself is produced only at a high cell density (HCD) (for a review, see reference 19). The two input signals (e.g., HCD signaled through HapR and chitin signaled through TfoX) merge in the production of the QS- and TfoX-dependent regulator QstR [22], which is required for the production of the pilus-unrelated part of the DNA-uptake machinery [15,16,17] and for the induction of the T6SS [8] (Fig. 1)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
