Contributions of F‐specific subunits to the F plasmid‐encoded type IV secretion system and F pilus. Issue 5 (26th April 2022)

• Record Type: Journal Article
• Authors: Kishida, Kouhei; Bosserman, Rachel E.; Harb, Laith; Khara, Pratick; Song, Liqiang; Hu, Bo; Zeng, Lanying; Christie, Peter J.
• Is Part Of: Molecular microbiology. Volume 117:Issue 5(2022)
• Page Start: 1275
• Page End: 1290
• Publication Date: 2022-04-26
• Subjects: conjugative pilus -- cryoelectron tomography -- DNA conjugation -- fluorescence microscopy -- horizontal gene transfer; Molecular microbiology -- Periodicals; 572.829
• DOI: 10.1111/mmi.14908
• Languages: English
• ISSNs: 0950-382X

Abstract

Abstract: F plasmids circulate widely among the Enterobacteriaceae through encoded type IV secretion systems (T4SSF s). Assembly of T4SSF s and associated F pili requires 10 VirB/VirD4‐like Tra subunits and eight or more F‐specific subunits. Recently, we presented evidence using in situ cryoelectron tomography (cryoET) that T4SSF s undergo structural transitions when activated for pilus production, and that assembled pili are deposited onto alternative basal platforms at the cell surface. Here, we deleted eight conserved F‐specific genes from the MOBF12C plasmid pED208 and quantitated effects on plasmid transfer, pilus production by fluorescence microscopy, and elaboration of T4SSF structures by in situ cryoET. Mutant phenotypes supported the assignment of F‐specific subunits into three functional Classes: (i) TraF, TraH, and TraW are required for all T4SSF ‐associated activities, (ii) TraU, TraN, and TrbC are nonessential but contribute significantly to distinct T4SSF functions, and (iii) TrbB is essential for F pilus production but not for plasmid transfer. Equivalent mutations in a phylogenetically distantly related MOB12A F plasmid conferred similar phenotypes and generally supported these Class assignments. We present a new structure‐driven model in which F‐specific subunits contribute to distinct steps of T4SSF assembly or activation to regulate DNA transfer and F pilus dynamics and deposition onto alternative platforms. Abstract : Bacteria disseminate mobile genetic elements such as F plasmids, which often code for resistance to antibiotics, to other bacteria by a process termed conjugation. Here, we characterize the contributions of a set of highly conserved proteins to the conjugative transfer of F plasmids. We show that these proteins play distinct roles in assembly and activation of the F‐encoded conjugation machinery.