Bacterial Conjugation in Gram-Negative Bacteria

Abstract

Bacterial conjugation is one of the fundamental processes for gene dissemination or horizontal gene transfer in nature and involves the transfer of DNA between bacteria in close apposition with one another. This chapter pulls together the information currently available on conjugative systems in gram-negative bacteria; reassess the information available before 1994, the year the sequences of two important gram-negative conjugation systems, F and RP4, appeared; and begin to construct a way of classifying and naming the genes from a plethora of conjugative systems, many of which appear to be chimeras of F and RP4. The junction between mating cells requires that the outer membranes of the two cells come into close apposition. The mechanism of active disaggregation of mating cells is unknown but might be related to the finding that transfer of IncI1 plasmids is terminated by a process requiring de novo protein synthesis in the new transconjugant. The relaxase, which is asymmetric in shape, is situated at the entry portal (base) of the pilus and is translocated as a first step in the conjugative process during mating-pair stabilization. Its inclusion in the conjugative pore could be in response to the triggering of conjugative DNA processing in the donor cell. The chapter discusses DNA processing and transport, the nature of the signal that triggers transfer, and mobilizable plasmids. It talks about F-like systems and P-like systems for which detailed analyses of gene regulation exist.