Gene transfer among bacteria under conditions of nutrient depletion in simulated and natural aquatic environments

Abstract

Gene transfer among microorganisms has been well demonstrated in laboratory microcosms and in situ, under non-limiting nutrient conditions. The literature contains conflicting opinions, however, as to whether such processes could occur in the absence of nutrients. This review summarises the evidence for the occurrence of gene transfer by conjugation, transformation and transduction among non-growing bacteria in nutrient depleted environments. Conjugation by selftransmissible, or by non-selftransmissible but mobilisable, plasmids has been shown to occur among environmental isolates of Escherichia coli, Enterobacter cloacae, Pseudomonas aeruginosa and marine Vibrio strains. Transduction and transformation have been demonstrated in isolates of P. aeruginosa and marine Vibrio strains, respectively. It is possible that the mechanisms of these processes may be different in non-growing cells in nutrient depleted conditions, compared to those occurring in cells growing in rich media.