Discovering and exploiting molecular markers to follow reductive dechlorination in growndwater and sediments

Microbial resource management is an emerging discipline aimed at the exploitation of complex microbial communities for addressing practical problems. For a straightforward management of such microbial communities the availability of suitable markers for process monitoring and detection of the microbial activities is an essential requirement especially for those processes occurring at low rates. In the environmental field an impressive series of novel previously-non-recognized microbial processes have been discovered in the last twenty years, including those occurring in anaerobic conditions or along oxic/anoxic interfaces. Among others the anaerobic oxidation of ammonium and methane or the reductive dehalogenation. The latter is very interesting for the removal of chlorinated pollutants that represent a major class of persistent contaminants. These include chlorinated solvents that can contaminate groundwater due to the relatively high water solubility and polychlorinated byphenils (PCBs) that can be major contaminants of soil and sediments. In anaerobic conditions several bacteria have been shown to be capable of flowing electrons deriving from hydrogen or reduced organic compounds using halogenated compounds as electron acceptors. Such a metabolic process determines the displacement of the halogen with a net dehalogenation of the molecule. Despite these processes can be rather slow, they represent a useful tool for the detoxification of environmental matrices from the chlorinated pollutants and can be usefully exploited in situ at relatively low costs, provided that a suitable monitoring system for following the process is available. Here we show the search of taxonomic and metabolic gene markers related to the dehalogenation of 1,2-dichloroethane (1,2-DCA) and polychlorinated byphenils. By establishing suitable microcosms we have enriched specific microbiomes capable of addressing the reductive dechlorination of 1,2- DCA from a polluted groundwater and PCBs from contaminated marine sediments. By studying the response of the corresponding microbial communities to the spiking of electron donors we were able to identify novel strains with reductive dechlorination potential and fishing out from the microbial metagenome of the systems novel reductive dehalogenases specifically linked to the dechlorination of 1,2-DCA or associated to the dechlorination of PCBs. The diversity of such enzymes their novelty and specificity for given chlorinated compounds is discussed together with the potential of their genes as suitable markers to follow the process of reductive dechlorination in the field. This work has been conducted in the frame of the European Community FP7-KBBE-2010-4 project ULIXES, grant agreement N. 266473.