SbcB facilitates natural transformation in Vibrio cholerae in an exonuclease-independent manner

Natural transformation (NT) is a conserved mechanism of horizontal gene transfer in bacterial species. During this process, DNA is taken up into the cytoplasm where it can be integrated into the host genome by homologous recombination. We have previously shown that some cytoplasmic exonucleases can inhibit NT by degrading ingested DNA prior to its successful recombination. Here, however, we demonstrate that the exonuclease SbcB counterintuitively promotes NT in Vibrio cholerae . Through a systematic analysis of the distinct steps of NT, we show that SbcB acts downstream of DNA uptake into the cytoplasm, but upstream of recombinational branch migration. Through mutational analysis, we show that the SbcB promotes NT in a manner that does not rely on its exonuclease activity. Finally, we provide genetic evidence that SbcB directly interacts with the primary bacterial recombinase, RecA. Together, these data advance our molecular understanding of horizontal gene transfer in V. cholerae , and reveal that SbcB promotes homologous recombination during NT in a manner that does not rely on its canonical exonuclease activity.