Indexed on: 14 Oct '19Published on: 13 Oct '19Published in: Applied and environmental microbiology
Conjugative transfer of gram-negative bacterial plasmids to recipient cells is often mediated by type IV secretion machinery. Experimental investigations into the minimal gene sets required for efficient conjugative transfer suggest that such gene sets are variable depending on plasmids. We have been analyzing the conjugative transfer of -derived and IncP-9 plasmids, NAH7 and pWW0, whose conjugation systems belong to the MPF type. Our deletion analysis and synthetic biology analysis in this study showed that these plasmids require previously uncharacterized genes, (formerly ) and its functional homolog, , respectively, for their efficient conjugative transfer. MpfK was localized in periplasm, and had four cysteine residues whose intramolecular or intermolecular disulfide bond formation was suggested to be important for efficient conjugative transfer. The homologs were specifically carried by many MPF-type plasmids, including non-IncP-9 plasmids such as R388 and R751. Intriguingly, the homologs from the two non-IncP-9 plasmids were not required for conjugation of their plasmids, but were able to complement efficiently the transfer defect of the NAH7 mutant. Our results suggested the importance of the homologs for conjugative transfer of MPF-type plasmids. IncP-9 plasmids are important mobile genetic elements for the degradation of various aromatic hydrocarbons. Elucidation of conjugative transfer of such plasmids is expected to greatly contribute to our understanding of its role in the bioremediation of polluted environments. The present study mainly focused on the conjugation system of NAH7, a well-studied and naphthalene-catabolic IncP-9 plasmid. Our analysis showed that the NAH7 conjugation system uniquely requires, in addition to the conserved components of the type IV secretion system (T4SS), a previously uncharacterized periplasmic protein, MpfK, for successful conjugation. Our findings collectively revealed a unique type of T4SS-associated conjugation system in the IncP-9 plasmids. Copyright © 2019 American Society for Microbiology.