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Anaerobic reductive dehalogenation of organohalides in enrichment cultures from marine sediments of Venice lagoon.

Rodopoulou Ioanna-Andrianna

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Summary

Particular attention in recent years has been given to organohalide pollution of subsurface environments in industrialized areas. Microbial reductive dehalogenation plays an important role in decontamination of soil and sediments as strictly anaerobic microorganisms have evolved using naturally occurring halogenated organics as their terminal electron acceptor. To investigate the activity of these unusual organisms, an indigenous microbial community of a PCB-impacted sediment from Brentella Canal (Venice lagoon, Italy) was enriched in defined mineral media through subculturing from TCE- amended slurry microcosms. Reductive dechlorination process was tested initially in the presence of lactate and pyruvate, two organic acids with the ability to serve as substrates during cometabolic anaerobic reduction. Bacteria's activity was stimulated as they completely bioconverted TCE simultaneously to cis- and trans-DCE within 6 weeks with no lag phase. The cis-isomer was the major intermediate product at the beginning of chemical monitoring but after a few weeks the trans-isomer took the lead role in TCE dechlorination. This change could be ascribed as the action of a non-Dehalococcoides phylotype of the class Dehalococcoidia, namely phylotype VLD-1, which was considered as the main phylotype for the dehalogenation activity. For further test and enrichment, subculturing of lactate-fed microcosms was performed using the same defined mineral medium but amended with antibiotics. The presence of ampicillin, vancomycin and 2-bromoethanesulfonate did not inhibit TCE dechlorination activity since the dechlorinating VLD-1, which turned out to be tolerant to the antibiotics, was enriched. Finally, another set of microcosms from cultures with lactate was prepared to test dehalogenation in the presence of different electron acceptors including TCE in the defined mineral medium. In contrast with the positive results cultures showed before subculturing while in sediment-slurry medium, in the defined medium none of the cultures exhibited dehalogenation activity except for the ones amended with TCE. This finding suggested that due to subculturing and enrichment certain synergistic bacteria were lost whose presence was significant for the production of enzymes catalyzing dehalogenation on several organohalides.

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