Methane oxidation as a method to evaluate the removal of 2,4-dichlorophenoxyactic acid (2,4-D) from soil by plasmid-mediated bioaugmentation

Abstract

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is known to inhibit methanotrophic bacteria. Methane oxidation was therefore used as a parameter to evaluate the residual 2,4-D after bioaugmentation of an agricultural soil. Several strains harbouring catabolic plasmids which code for the degradation of this pesticide, were compared for their potential to alleviate the negative impact of 2,4-D on methane oxidation by soil microorganisms. Three indigenous soil bacteria which contain the 2,4-D degradative plasmid pEMT1k, obtained from a donor by in situ plasmid transfer in previous experiments, were compared with Ralstonia eutropha JMP134, which harbours the well studied 2,4-D degradative plasmid pJP4. In addition a Pseudomonas putida UWC3(pEMT1k), which does not degrade 2,4-D, was used as donor to investigate the potential bioaugmentation through in situ transfer of the catabolic genes towards the indigenous soil bacteria. Both the strains that can degrade 2,4-D as well as the P. putida donor strain could enhance the recovery of methane oxidation by increasing the rate of degradation of 2,4-D and thus removing its toxic effect on the methane oxidising microbial populations. In all cases the time needed to oxidise methane was consistently shorter (4^10 days) in a 2,4-D treated soil inoculated with the strains, than in the non-inoculated 2,4-D treated soil, but still longer (5^10 days) than in the soil without 2,4-D. These data indicate that pesticide residues as well as their toxic effect on important soil microbial processes could be successfully removed from the soil by addition of well adapted specialised strains with the genetic information required to degrade the applied pesticides. z 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Biodegradation of hexachlorocyclohexane (HCH) by microorganisms

“…Bioaugmentation (inoculation with previously acclimated HCH-degrading microorganisms that are not necessarily indigenous to the site) is a less popular approach, albeit a potentially effective one. Bioaugmentation and enhanced natural attenuation have been successful approaches for enhancing remediation of soils contaminated with a variety of xenobiotic compounds (Cunningham & Philp 2000;Juhasz et al 2000;Manzano et al 2003;Newcombe & Crowley 1999;Runes et al 2001;Top et al 1999). Each of these approaches can enhance bioremediation, either by increasing the population of microorganisms in soil capable of degrading the target contaminant, or by rendering the contaminant more bioavailable.…”

Stereospecific effect of hexachlorocyclohexane on activity and structure of soil methanotrophic communities

“…The MELC was used for further short-term experiments of the effect of HCH. The procedure for analysis of methane has been described previously (Top et al, 1999;Seghers et al, 2003b).…”

Catabolic mobile genetic elements and their potential use in bioaugmentation of polluted soils and waters

“…Since E. coli is not a suitable strain for bioremediation purposes, the previous study was extended with the same soil, now using P. putida UWC3 as donor of plasmid pEMT1. Again, transfer of plasmid pEMT1 was observed and correlated with an enhanced degradation of 2,4-D. A few transconjugants that harbored pEMT1 and degraded 2,4-D were identi¢ed as R. eutropha [38]. Since the donor strain was still present when degradation started and was recently shown to partially degrade 2,4-D in liquid cultures and sterile soil [39], its involvement in the degradation of 2,4-D could not be totally excluded.…”