Control of genes for conjugative transfer of plasmids and other mobile elements

Abstract

Conjugative transfer is a primary means of spread of mobile genetic elements (plasmids and transposons) between bacteria.It leads to the dissemination and evolution of the genes (such as those conferring resistance to antibiotics) which are carried by the plasmid. Expression of the plasmid genes needed for conjugative transfer is tightly regulated so as to minimise the burden on the host. For plasmids such as those belonging to the IncP group this results in downregulation of the transfer genes once all bacteria have a functional conjugative apparatus. For F-like plasmids (apart from F itself which is a derepressed mutant) tight control results in very few bacteria having a conjugative apparatus. Chance encounters between the rare transfer-proficient bacteria and a potential recipient initiate a cascade of transfer which can continue until all potential recipients have acquired the plasmid. Other systems express their transfer genes in response to specific stimuli. For the pheromone-responsive plasmids of Enterococcus it is small peptide signals from potential recipients which trigger the conjugative transfer genes. For the Ti plasmids of Agrobacterium it is the presence of wounded plants which are susceptible to infection which stimulates T-DNA transfer to plants. Transfer and integration of T-DNA induces production of opines which the plasmid-positive bacteria can utilise. They multiply and when they reach an appropriate density their plasmid transfer system is switched on to allow transfer of the Ti plasmid to other bacteria. Finally some conjugative transfer systems are induced by the antibiotics to which the elements confer resistance. Understanding these control circuits may help to modify management of microbial communities where plasmid transfer is either desirable or undesirable. z 1998 Published by Elsevier Science B.V.

Conjugation is necessary for a bacterial plasmid to survive under protozoan predation

“…This would promote the ability of plasmid-harbouring individuals to rapidly reseed any emerging plasmid-free individuals. In the absence of predation, the population rapidly reaches the carrying capacity of the system, possibly shutting down active conjugation [18], which allows a sub-population of plasmid-free individuals to establish and grow over time as the culture is renewed.…”

Conjugative Plasmid Transfer in Gram-Positive Bacteria

“…However, IncP transfer genes are not expressed constitutively. In fact, their expression is regulated by complex local autoregulatory circuits as well as by global regulators, resulting in the coordinated expression of transfer genes with other plasmid functions (52,225).…”

Two novel conjugative plasmids from a single strain of Sulfolobus

“…Upon conjugation, pSOG2 actively replicates to a high copy number, but subsequently replication appears to be strongly down-regulated to reduce the copy number and to maintain the plasmid stably in its new host. In bacterial CPs, regulatory circuits involving specialized transcriptional regulators have been described (Zatyka & Thomas, 2002). There are as many as six ORFs that potentially play similar roles in the pSOG plasmids.…”