Effects of stress and other environmental factors on horizontal plasmid transfer assessed by direct quantification of discrete transfer events

Abstract

Selection pressure may affect the horizontal transfer of plasmids. The inability to distinguish between gene transfer and the growth of transconjugants complicates testing. We have developed a method that enables the quantification of discrete transfer events. It uses large numbers of replicate matings (192 or 384) in microtiter wells and the counting of transfer-positive and transfer-negative wells. We applied the method to study the transfer of the IncP1 plasmid pRO103 between Escherichia coli and Pseudomonas putida strains. pRO103 encodes resistance to mercury and tetracycline and partial degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The results showed positive correlation between transfer and donor metabolic activity, and an optimal temperature for transfer of 29 degrees C. On stimulation of donor activity, the optimal temperature was decreased to 24.5 degrees C. HgCl(2) above 1.0 microg L(-1) negatively affected transfer, whereas 2,4-D up to 0.3 mM had no effect. The negative effect of mercury was shown to be a result of stressing of the recipient. No effects of mercury on transfer could be detected by traditional filter mating. Thus, the method is superior to filter mating and, as the experimental design allows the manipulation of individual parameters, it is ideal for the assessment and comparison of effects of environmental factors on plasmid transfer.

Cultivation of Hard-To-Culture Subsurface Mercury-Resistant Bacteria and Discovery of New merA Gene Sequences

“…Since the diversity of bacterial communities generally is negatively affected by mercury stress (9,21), this high diversity of the mercury-resistant subpopulations was surprising. Mercury has been shown to negatively affect the conjugal transfer of plasmids (12). However, considering the long history of mercury contamination, the low concentration of bioavailable mercury, and the likely presence of nonexposed microniches, a plausible explanation for the high diversity of the mercury-resistant subpopulations is horizontal transfer of mobile genetic elements carrying the mer operon (19,24).…”

Elevated temperatures and carbon dioxide concentrations: effects on selected microbial activities in temperate agricultural soils

“…In a laboratory experiment, plasmid HGT frequency between E. coli and Pseudomonas putida strains increased linearly from 50 to about 230 transfer events after 5 h of incubation when the temperature was raised from 5 to 29°C. At 35.5°C, plasmid transfer events decreased considerably (Johnsen and Kroer 2007). In plate transformation assay studies, natural transformation occurred optimally at high temperatures.…”

Bioremediation: Plasmid-Mediated Bioaugmentation of Microbial Communities – Experience from Laboratory-Scale Bioreactors

“…However, other species, including Escherichia coli, Erwinia chrysanthemi, Hydrogenophaga palleronii, Serratia, and Burkholderia species, have been shown to be recipients of pWW0 (Benson and Shapiro, 1978;Nakazawa et al, 1978;Nancharaiah et al, 2003;Ramos-Gonzalez et al, 1991;Sarand et al, 2000). However, the transfer of pWW0 depends not only on the donor strains and recipient pool but also on environmental factors such as nutrient concentration and temperature (Johnsen and Kroer, 2007;Fox et al, 2008). Conjugative transfer of plasmid pWW0 was accomplished efficiently on plates (Christensen et al, 1996), in biofilm or bioaggregates Nancharaiah et al, 2003), soils (Sarand et al, 2000), on bush bean leaves (Normander et al, 1998), and in activated sludge communities (Nancharaiah et al, 2003(Nancharaiah et al, , 2008Venkata Mohan et al, 2009).…”