17 - Mechanisms of Gene Exchange Between Bacteria

Abstract

Gene movement between bacteria is achieved by the three quasi-sexual processes of bacterial conjugation, transduction, and transformation. Each involves unidirectional transfer of just part of the genome of a donor bacterium to the recipient cell but is distinct by mechanism and randomness of the genomic fragment transferred. Bacterial conjugation, the dedicated transfer process of plasmids, requires a specific contact between the donor and recipient bacterium and results in the ordered transmission of a unique DNA strand to the recipient cell. In contrast, natural transformation and transduction support transfer of non-specific genomic fragments; the systems differ considerably at the mechanistic level, since transformation involves uptake of naked DNA from the extracellular environment whereas transduction entails transfer of non-viral DNA within a bacteriophage particle. This chapter reviews molecular aspects of gene movement between bacteria, focusing on medical implications. The chapter considers the significance of gene transfer and transmissible elements to medically important bacteria and addresses molecular understanding of gene transfer by bacterial conjugation, transformation and transduction. Finally, the barriers that operate, following transfer itself, to inhibit the integration of transferred DNA into the genome of the recipient cell are reviewed.