Protein Transfer through an F Plasmid-Encoded Type IV Secretion System Suppresses the Mating-Induced SOS Response
Abu Amar M. Al Mamun, Kouhei Kishida, Peter J. Christie
Abstract
Many bacteria carry plasmids and other mobile genetic elements (MGEs) whose conjugative transfer through encoded type IV secretion systems (T4SSs), or "mating" channels, can lead to a rapid intra- and interspecies proliferation of genes encoding resistance to antibiotics or heavy metals or virulence traits. Here, we show that a model IncF plasmid-encoded T4SS translocates not only DNA but also several proteins intercellularly. The repertoire of translocated proteins includes the plasmidic SOS inhibitor protein PsiB, single-stranded DNA-binding protein SSB, and several partitioning proteins. We demonstrate that intercellular transmission of PsiB and SSB suppresses the SOS response, which is triggered in recipient cells upon acquisition of the single-stranded DNA transfer intermediate during mating. Our findings identify a new biological function for conjugative protein translocation in mitigating potentially deleterious consequences to plasmid and genome integrity resulting from SOS-induced recombination and mutation events.