Correlation of Dehalococcoides 16S rRNA and chloroethene reductive dehalogenase genes to different geochemical conditions in chloroethene-contaminated groundwater

Quantitative analysis of genes that code for Dehalococcoides 16S rRNA and chloroethene reductive dehalogenases TceA, VcrA and BvcA was done on groundwater sampled from 150 monitoring wells spread over 11 chlorinated ethene polluted European locations. Redundancy analysis (RDA) was used to relate molecular data to geochemical conditions. Dehalococcoides spp. 16S rRNA- and VC-reductase genes were present at all tested locations in concentrations up to 10(6) gene copies per ml groundwater. However, differences between and also within locations were observed. Variation in Dehalococcoides spp. 16S rRNA gene copy numbers were most strongly correlated to dissolved organic carbon concentration (DOC) in groundwater and to conditions appropriate for biodegradation of chlorinated ethenes (EPA-score). In contrast, vcrA gene copy numbers correlated most significantly to VC and chlorinated ethene concentrations. Interestingly, bvcA and especially tceA were more correlated with oxidizing conditions. In groundwater microcosms, dechlorination of 1 mM VC was correlated to an increase of vcrA and/or bvcA gene copies by 2-4 orders of magnitude. Interestingly, in 34% of the monitoring wells and in 40% of the active microcosms, the amount of individual VC-reductase gene copies exceeded that of Dehalococcoides spp. 16S rRNA gene copies. It is concluded that the geographical distribution of the genes was not homogeneous, depending on the geochemical conditions, whereby tceA and bvcA correlated to more oxidized conditions than Dehalococcoides spp. 16S rRNA and vcrA. Because variation in VC-reductase gene numbers was not directly correlated to variation in Dehalococcoides spp., VC-reductase genes are better monitoring parameters for VC dechlorination capacity than Dehalococcoides spp.