Control of Competence in Vibrio fischeri.

species, including the squid symbiont , become competent to take up DNA under specific conditions. For example, becomes competent when grown in the presence of chitin oligosaccharides or upon overproduction of the competence regulatory factor TfoX. While little is known about the regulatory pathway(s) that controls competence, this microbe encodes homologs of factors that control competence in the well-studied To further develop as a genetically tractable organism, we evaluated the roles of some of these competence homologs. Using TfoX-overproducing cells, we found that competence depends upon LitR, the homolog of master quorum-sensing and competence regulator HapR, and upon homologs of putative pilus genes that in facilitate DNA uptake. Disruption of genes for negative regulators upstream of LitR, namely, the LuxO protein and the small RNA (sRNA) Qrr1, resulted in increased transformation frequencies. Unlike LitR-controlled light production, however, competence did not vary with cell density under overexpression conditions. Analogous to the case with , the requirement for LitR could be suppressed by loss of the Dns nuclease. We also found a role for the putative competence regulator CytR. Finally, we determined that transformation frequencies varied depending on the TfoX-encoding plasmid, and we developed a new dual and overexpression construct that substantially increased the transformation frequency of a less genetically tractable strain. By advancing the ease of genetic manipulation of , these findings will facilitate the rapid discovery of genes involved in physiologically relevant processes, such as biofilm formation and host colonization. The ability of bacteria to take up DNA (competence) and incorporate foreign DNA into their genomes (transformation) permits them to rapidly evolve and gain new traits and/or acquire antibiotic resistances. It also facilitates laboratory-based investigations into mechanisms of specific phenotypes, such as those involved in host colonization. has long been a model for symbiotic bacterium-host interactions as well as for other aspects of its physiology, such as bioluminescence and biofilm formation. Competence of can be readily induced upon overexpression of the competence factor TfoX. Relatively little is known about the competence pathway, although homologs of factors known to be important in competence exist. By probing the importance of putative competence factors that control transformation of , this work deepens our understanding of the competence process and advances our ability to genetically manipulate this important model organism.