Gene transfer in the aquatic environment: persistence and mobilization of the catabolic recombinant plasmid pD10 in the epilithon

Abstract

This study investigated mobilization and persistence of the recombinant, catabolic plasmid pDlO in laboratory microcosms by natural mobilizing plasmids, recently isolated from epilithic bacteria by exogenous isolation in Pseudomonas putida, as opposed to their isolation in the strains in which they occur in situ. Initial experiments in simple, beaker microcosms were used to optimize conditions for selection of the donor, recipient and transconjugant populations. Studies in a recirculating stream microcosm showed that donor, P. putida KT2440(pDIO, pQKH6), and recipient, P. putida UWCG, populations, although declining with time, were able to survive for three weeks and that colonization and survival was predominantly in the epilithon of the microcosm rather than in the liquid phase. Transconjugants UWC6(pD10, pQKH6) were also isolated from epilithon, showing that plasmid pDlO had been mobilized b y plasmid pQKH6. The donor strain was able to survive a t 100-fold greater numbers than the recipient, but transconjugants were not isolated after day 15. Separate inoculation of the donor and recipient strains into the microcosm showed that they were able to colonize other stones, where transconjugants then arose as a direct result of plasmid transfer within the epilithon. A catechol2,3-dioxygenase gene, tdnC, was used to facilitate identification of donors and transconjugants. Preliminary laboratory matings showed that pDlO transferred to indigenous epilithic strains identified as Pseudomonas fluorescens, P. chlororaphis and P. aureofaciens. These results suggest that in the absence of selection, mobilization of introduced recombinant genes encoded by pDlO occurs at easily detectable frequencies, even in an oligotrophic environment.

Plasmid Introduction in Metal-Stressed, Subsurface-Derived Microcosms: Plasmid Fate and Community Response

“…At very high levels of heavy metal contamination (e.g., Ͼ1% by weight), most bacterial life is inhibited, community diversity is severely reduced, and only a very limited, extremely resistant fraction survives. At lower concentrations (approximately 1 to 10 mM individual metals), microbial activity is temporarily impaired, but acquisition and expression of heavymetal resistance genes can occur, and the main events in community dynamics may be the spread of metal resistance genes, often plasmid or transposon encoded (26,34), and outgrowth of the intrinsic heavy-metal-resistant populations (1,22). At heavy metal levels at or below toxic concentrations (Ͻ1 mM), the changes in community dynamics have not been well documented.…”

Safety Assessment of Transgenic Organisms, Volume 4

“…These habitats offer very different conditions to their bacterial inhabitants. The presence of nutrients as well as colonisable surfaces is particularly important as such sites are known to support large densities of metabolically-active micro-organisms (Hill et al, 1994). In contrast, bulk water can be a nutrient-poor environment which may induce a (starvation) stress response in bacterial cells.…”

“…Further, sediments, which are often rich in organic material, typically support bacterial populations exceeding those found in bulk water by several orders of magnitude . Biologically diverse and metabolically active communities can also be found in the epilithon of stones in rivers or lakes (Hill et al, 1994; and within other biofilms that form at solid/water interfaces. Micro-organisms within the epilithon are components of the extensive polysaccharide matrix which protects cells and adsorbs dissolved and particulate organic matter from the overlying water.…”

“…Nevertheless, given the capability of many bacteria to occur in either sessile forms in micro-colonies or biofilms, or in motile forms, and thus to potentially connect spatially-separated biofilms, aquatic habitats provide important sites for cell-to-cell contacts resulting in HGT between bacteria . Using both microcosm and in situ experiments, HGT between bacterial hosts has been shown to occur in drinking water, river water and epilithon (Hill et al, 1994(Hill et al, , 1996, lake water, seawater, marine sediment and wastewater . HGT thus appears to be a common process in aquatic environments, particularly in specific niches where nutrients are more abundant.…”

Biological Cr(VI) Reduction: Microbial Diversity, Kinetics and Biotechnological Solutions to Pollution

“…A similar process can be applied using genetically engineered linear DNA called transposons. Although studies have been conducted using these techniques in laboratory microcosms, the application in actual environments has not been attempted (Hill et al, 1994). In the future, it is foreseeable that these methods will find wide application for the new varieties of recalcitrant pollutants being discharged into the environment from several sources.…”