Conjugative Plasmid Transfer in Gram-Positive Bacteria

Abstract

Conjugative transfer of bacterial plasmids is the most efficient way of horizontal gene spread, and it is therefore considered one of the major reasons for the increase in the number of bacteria exhibiting multiple-antibiotic resistance. Thus, conjugation and spread of antibiotic resistance represents a severe problem in antibiotic treatment, especially of immunosuppressed patients and in intensive care units. While conjugation in gram-negative bacteria has been studied in great detail over the last decades, the transfer mechanisms of antibiotic resistance plasmids in gram-positive bacteria remained obscure. In the last few years, the entire nucleotide sequences of several large conjugative plasmids from gram-positive bacteria have been determined. Sequence analyses and data bank comparisons of their putative transfer (tra) regions have revealed significant similarities to tra regions of plasmids from gram-negative bacteria with regard to the respective DNA relaxases and their targets, the origins of transfer (oriT), and putative nucleoside triphosphatases NTP-ases with homologies to type IV secretion systems. In contrast, a single gene encoding a septal DNA translocator protein is involved in plasmid transfer between micelle-forming streptomycetes. Based on these clues, we propose the existence of two fundamentally different plasmid-mediated conjugative mechanisms in gram-positive microorganisms, namely, the mechanism taking place in unicellular gram-positive bacteria, which is functionally similar to that in gram-negative bacteria, and a second type that occurs in multicellular gram-positive bacteria, which seems to be characterized by double-stranded DNA transfer

Actinomycete integrative and conjugative pMEA-like elements of Amycolatopsis and Saccharopolyspora decoded

“…Although not shown thus far, it has been suggested that the genes responsible for the widespread resistance to aminoglycoside antibiotics in pathogens originate from soil bacteria, notably the actinomycetes, which are the most prominent aminoglycoside producers, and that the resistance genes were spread to other bacteria via horizontal gene transfer (Benveniste and Davies, 1973;Marshall et al, 1998;Grohmann et al, 2003). Several AICEs are able to mobilise chromosomal markers (Moretti et al, 1985;Hopwood et al, 1984;Brown et al, 1988b;Vrijbloed, 1996;Smokvina et al, 1988;Bibb et al, 1981), suggesting that they may play an important role in horizontal gene transfer and evolution of genome plasticity.…”

The versatile bacterial type IV secretion systems

“…The largest subfamily, the conjugation systems, are found in most species of Gram-negative and Grampositive bacteria. These systems mediate DNA transfer both within and between phylogenetically diverse species, and some systems even deliver DNA to fungi, plants and human cells 2,[9][10][11][12][13] . Conjugation is an important contributor to genome plasticity, and therefore bacterial fitness under changing environmental conditions, as encountered during infection of the human host.…”

Risks from GMOs due to Horizontal Gene Transfer

“…Conjugation is widespread throughout bacteria and is the most important mechanism for translocating DNA between bacteria (Espinosa-Urgel, 2004; Grohmann et al, 2003). In the natural environment conjugation occurs primarily between closely-related strains or species.…”