Abstract
Type IV Secretion Systems (T4SSs) are membrane-spanning multiprotein complexes dedicated to protein secretion or conjugative DNA transport (conjugation systems) in bacteria. The prototype and best-characterized T4SS is that of the Gram-negative soil bacterium Agrobacterium tumefaciens. For Gram-positive bacteria, only conjugative T4SSs have been characterized in some biochemical, structural, and mechanistic details. These conjugation systems are predominantly encoded by self-transmissible plasmids but are also increasingly detected on integrative and conjugative elements (ICEs) and transposons. Here, we report regulatory details of conjugation systems from Enterococcus model plasmids pIP501 and pCF10, Bacillus plasmid pLS1, Clostridium plasmid pCW3, and staphylococcal plasmid pSK41. In addition, regulation of conjugative processes of ICEs (ICEBs1, ICESt1, ICESt3) by master regulators belonging to diverse repressor families will be discussed. A special focus of this review lies on the comparison of regulatory mechanisms executed by proteins belonging to the RRNPP family. These regulators share a common fold and govern several essential bacterial processes, including conjugative transfer.
Highlights
Horizontal gene transfer (HGT) is leadingly involved in the evolution of bacteria and in the dissemination of antibiotic resistances and pathogenicity determinants
Factors needed for conjugative processes can be encoded on plasmids or integrative and conjugative elements (ICEs)
The following sections concentrate on selected plasmids or ICEs from different G+ species, ranging from broad-host range plasmids that produce their conjugative systems constitutively at low levels to inducible/repressible plasmids responding to stimuli from small peptides, called pheromones or autoinducers
Summary
Horizontal gene transfer (HGT) is leadingly involved in the evolution of bacteria and in the dissemination of antibiotic resistances and pathogenicity determinants. Factors needed for conjugative processes can be encoded on plasmids or integrative and conjugative elements (ICEs). Gram-Positive Conjugation Regulation systems, which facilitate the transport of ss-DNA via a molecular machinery encoded by multiple genes that are mostly organized in a single operon These systems comprise a relaxase, a coupling protein and a mating pair formation (MPF) complex. Excision and re-integration, are required, ICEs harbor genes that resemble factors of lysogenic phages (Wozniak and Waldor, 2010) These elements show a modular structure with genes of the same/similar function clustered together and usually consist of a maintenance module (responsible for integration and excision), a dissemination module (required for conjugative transfer), and a regulation module (Burrus and Waldor, 2004). ICEs harbor genes beneficial for their host under specific conditions, e.g. mediating resistance to antimicrobial drugs, heavy metals, and infections by phages (Burrus and Waldor, 2004; Burrus, 2017)
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