Genetic bioaugmentation as an effective method for in situ bioremediation: functionality of catabolic plasmids following conjugal transfers

Abstract

Genetic bioaugmentation is an in situ bioremediation method that stimulates horizontal transfer of catabolic plasmids between exogenous donor cells and indigenous bacteria to increase the biodegradation potential of contaminants. A critical outcome of genetic bioaugmentation is the expression of an active catabolic phenotype upon plasmid conjugation. Using a pWW0-derivative TOL plasmid, we showed that certain genetic characteristics of the recipient bacteria, including genomic guanine-cytosine (G + C) content and phylogeny, may limit the expression of the transferred catabolic pathway. However, such genetic limitations observed in transconjugants could be overcome by the presence of an additional carbon source. Glucose and Luria-Bertani broth were shown to enhance the toluene degradation rates of transconjugants; these enhancement effects were dependent on transconjugant genomic G + C contents. Based on these observations, thorough genetic characterization of the indigenous microbial community in the contaminated environment of interest may provide a predictive tool for assessing the success of genetic bioaugmentation.

Figure 1.

Genetic bioaugmentation schematic.

Figure 2.

Specific toluene degradation rates of TOL plasmid-bearing strains exposed to toluene in the presence of 0, 10 and 25% (v/v) LB broth. Error bars represent the standard deviation of at least triplicate samples.

Figure 3.

Fold changes in specific toluene degradation rates induced by the addition of 1 g/L glucose (A) and 10% LB broth (B) in strains with varying genomic G + C contents. Error bars represent the standard deviation of at least triplicate samples.

Figure 4.

Transconjugant occurrence under varying selective pressures in soil slurry batch mating experiments. S. marcescens and P. fluorescens were used as recipient strains and mated with donor P. putida BBC443 cells in soil slurry under the presence or absence of Km and toluene. Error bars represent standard deviations of triplicate samples.