harveyi (Fig. 4), which encodes a V. cholerae

QS pathway (Hammer & Bassler, 2008). As with V. cholerae, the maximal transformation frequency occurred with the WT V. harveyi strain, which produces both CAI-1 and AI-2. Transformation decreases when only CAI-1 or AI-2 was provided, and was most impaired in the absence of either autoinducer (Fig. 4). We also measured transformation frequency of V. cholerae autoinducer-deficient recipient in response to WT V. parahaemolyticus and V. fischeri autoinducer donors. Transformation efficiency of these Vibrio strains followed a pattern of comEA-lux expression that matched the corresponding donor strains; the V. parahaemolyticus buy FK228 strain used produces both CAI-1 and AI-2 and promoted transformation with IWR 1 a frequency similar to V. harveyi. The V. fischeri strain tested (and another sequenced V. fischeri strain, data not shown) only encode for luxS (and not cqsA), and thus produce AI-2, but not CAI-1. Vibrio fischeri poorly promoted DNA uptake by the V. cholerae recipient (Fig. 4), consistent with AI-2 playing a minor role in natural transformation. Taken together, these observations support a model that

V. cholerae can switch to the competent state and acquire DNA horizontally in a chitinous environmental biofilm by responding to autoinducer signals derived from members of the multispecies consortium. Induction of the competence program in V. cholerae requires the chitin-responsive

TfoX pathway and the autoinducer-responsive QS pathway. When both systems are functional, DNA uptake machinery facilitates the transport of extracellular DNA into the bacterial cell, where it may be incorporated into the genome by homologous recombination (Hamilton & Dillard, 2006). Many Vibrios encode for chitin utilization and O-methylated flavonoid competence genes (Hunt et al., 2008; Gulig et al., 2009; Ng & Bassler, 2009; Pollack-Berti et al., 2010), which suggests the possibility that natural transformation may be a conserved mechanism for both pathogenic and nonpathogenic Vibrios to horizontally acquire virulence and other genes within a community. Recognizing that many Vibrios possess V. cholerae-like QS circuits and produce CAI-1 and AI-2, we examined the relationship between autoinducers production and DNA uptake. Specifically, we showed that (1) V. cholerae efficiently activated a comEA-lux reporter in response to self-produced autoinducers as well as purified autoinducers and (2) a V. cholerae autoinducer-deficient strain readily acquires DNA when co-cultured with purified autoinducers and also with autoinducers produced by other Vibrios within a chitinous mixed-species biofilm. These results support a model that V. cholerae can switch to the competent state in a chitinous environmental biofilm by responding to autoinducer molecules derived from members of the multispecies consortium.