Enhanced degradation of phenoxyacetic acid in soil by horizontal transfer of the tfdA gene encoding a 2,4-dichlorophenoxyacetic acid dioxygenase

Abstract

Few studies have investigated the possible impact of in situ gene transfer on the degradation of xenobiotic compounds in natural environments. In this work we showed that horizontal transfer of the tfdA gene, carried on plasmid pRO103, to phenol degrading recipient strains significantly increased the degradation rate of phenoxyacetic acid in sterile and non-sterile soil microcosms. The tfdA gene encodes a 2,4-dichlorophenoxyacetic acid/2-oxoglutarate dioxygenase and by complementation with the phenol degradation pathway an expanded catabolic substrate range, now including phenoxyacetic acid, is evolved. Presence of selective pressure had a positive effect on the emergence of transconjugants. However, even in the absence of phenoxyacetic acid transconjugant populations were detected and were kept at a constant level throughout the experimental period. The residuesphere (interface between decaying plant material and soil matrix) of dry leaves of barley was shown to be a hot-spot for gene transfer and presence of barley straw increased the conjugation frequencies in soil microcosms to the same extent as presence of organic nutrients. The results of this study indicate that dissemination of catabolic plasmids is a possible mechanism of genetic adaptation to degradation of xenobiotic compounds in natural environments, and that complementation of catabolic pathways possibly plays an important role in the evolution of new degradative capabilities. The application of horizontal gene transfer as a possible tool in bioremediation of contaminated sites is discussed.

Molecular Evidence for the Evolution of Metal Homeostasis Genes by Lateral Gene Transfer in Bacteria from the Deep Terrestrial Subsurface

“…To date, previous retrospective studies have had limited application to the study of LGT as a process that shapes the genetic diversity of natural communities. Rather, this issue has been addressed either by demonstrating transfer in microcosms (4,15) or by examining the potential for…”

“…The time scale for the acquisition of new genetic material by LGT, estimated to occur at a rate of 31 kb per 10 6 years in E. coli (32), may mean that microcosm studies have little relevance. Indeed, in many cases, LGT could be detected only following nutrient amendment (15), by inoculation of unrealistically high numbers of donor and recipient strains (4), or in the presence of selection for phenotypes encoded by the transferred genes (81). Observing LGT in microcosm studies simulating deep subsurface environments may be particularly difficult, as low population densities and metabolic rates may require prohibitively long incubation times before transformants and transconjugants are obtained.…”

Visual Evidence of Horizontal Gene Transfer between Plants and Bacteria in the Phytosphere of Transplastomic Tobacco

“…Moreover, this bacterium could be naturally transformed therein by artificially added or indigenous transgenic DNA (10,11). Yet, other plant compartments could be as propitious to HGT; for example, the residuesphere (i.e., the naturally degrading plant material at the interface with soil) has been shown to provide conditions for growth and conjugal gene transfer between indigenous soil bacteria (7,34). The litter and the residues of annual crops represent an important amount of final plant production, which are often left in the field after harvest and, in most cases, account for up to 60% of the world's plant biomass (14).…”

Application of Genetically Engineered Dioxygenase Producing Pseudomonas putida on Decomposition of Oil from Spiked Soil

“…The application of P. putida ZWL73 in contaminated soil with 4-chloronitoben-zene (4CNB) was investigated by Niu et al (32). In another research, it was found that tfdA gene located in plasmid pRO103 in phenol-degrading recipient strains leads to significantly biodegradation rate of phenoxy acetic acid in sterile and non-sterile soils (33). In the present study, the pUC18-nahH recombinant vector was generated and transferred into P. putida and degradation of oil in polluted soil was increased statistically via evaluation of phenanthrene and pyrene as an indicator.…”