| The discovery of natural transformation in the squid symbiont Vibrio fischeri presents an opportunity to explore the uptake and incorporation of DNA both as a mechanism of nucleotide acquisition in Vibrionaceae, and as a potential factor in the squid-vibrio mutualism. The biological relevance of DNA uptake may be for nutrition, genetic diversification, DNA repair, or supplementation of nucleotide pools. This study details the first report of natural competence of V. fischeri, and investigates this phenomenon further, focusing on its mechanism and regulatory inputs. V. fischeri is capable of transformation when grown in the presence of chitin oligosaccharides. Transformation in culture requires the paralogous genes tfoX and tfoY. Genetic competence of this organism is influenced by cell density, type-IV pili, and nutrient availability. The biological role of V. fischeri natural competence is subtle: in animal studies using E. scolopes, transformation-defective strains exhibited no fitness defect, and no genetic exchange amongst wild-type V. fischeri cells associated with a squid light organ was observed. However, V. fischeri cells do appear capable of using DNA as a nutrient source and express extracellular DNases. This study lays the groundwork for further exploration of Vibrio competence in the squid symbiont V. fischeri. |
