IncFV plasmid pED208: Sequence analysis and evidence for translocation of maintenance/leading region proteins through diverse type IV secretion systems.

Two phylogenetically distantly-related IncF plasmids, F and pED208, serve as important models for mechanistic and structural studies of F-like type IV secretion systems (T4SS F s) and F pili. Here, we present the pED208 sequence and compare it to F and pUMNF18, the closest match to pED208 in the NCBI database. As expected, gene content of the three cargo regions varies extensively, although the maintenance/leading regions (MLRs) and transfer (Tra) regions also carry novel genes or motifs with predicted modulatory effects on plasmid stability, dissemination and host range. By use of a Cre recombinase assay for translocation (CRAfT), we recently reported that pED208-carrying donors translocate several products of the MLR (ParA, ParB1, ParB2, SSB, PsiB, PsiA) intercellularly through the T4SS F. Here, we extend these findings by reporting that pED208-carrying donors translocate 10 additional MLR proteins during conjugation. In contrast, two F plasmid-encoded toxin components of toxin-antitoxin (TA) modules, CcdB and SrnB, were not translocated at detectable levels through the T4SS F. Remarkably, most or all of the pED208-encoded MLR proteins and CcdB and SrnB were translocated through heterologous T4SSs encoded by IncN and IncP plasmids pKM101 and RP4, respectively. Together, our sequence analyses underscore the genomic diversity of the F plasmid superfamily, and our experimental data demonstrate the promiscuous nature of conjugation machines for protein translocation. Our findings raise intriguing questions about the nature of T4SS translocation signals and of the biological and evolutionary consequences of conjugative protein transfer. • pED208 genome comparisons underscores mosaicism of F plasmids • Diversification of conjugation systems influences plasmid transfer and host range • Leading region proteins are co-translocated with the F plasmid during conjugation • Leading region proteins are translocated through heterologous conjugation systems • Conjugation systems translocate a large repertoire of proteins substrates [ABSTRACT FROM AUTHOR]