Functional diversity of reductive dehalogenases in a bacterial consortium degrading chloroethenes

Chlorinated hydrocarbon pollution threatens nature and human health due to its toxic and carcinogenic potential. Enrichment cultures were investigated for the bioremediation potential of tetrachloroethene (PCE). This process is based on bacterial anaerobic respiration in which the chlorinated compounds are used as electron acceptors (organohalide respiration, OHR). The key enzyme in OHR is the reductive dehalogenase (rdhA), which contains a corrinoid as cofactor. This study is focused on a better understanding of the functional diversity of rdhA genes and the interplay of OHR bacterial populations during PCE dechlorination. Two bacterial consortia containing different members of the Sulfurospirillum genus are investigated in our laboratory. The specificity in these consortia resides in the fact that although both producing highly similar RdhA enzymes, they catalyze reduction of PCE with different rate and substrate specificity. The culture harboring the enzyme PceATCE showed a higher PCE dechlorination activity and is involved in the dechlorination of PCE to trichloroethene (TCE), exclusively, whereas the culture which contains the enzyme PceADCE is able to dechlorinate PCE via TCE to cis-dichloroethene (cDCE). Corrinoid extraction data suggested that the corrinoid cofactor present in PceATCE is norpseudo-B12 as in the well-characterized PceA of S. multivorans which dechlorinates PCE to cDCE. Sulfurospirillum spp. are versatile OHR bacteria, therefore the question of rdhA gene regulation needs to be investigated. Pulse experiments with chloroethenes are performed on those consortia growing on fumarate as an alternative electron acceptor, followed by RNA extraction and qPCR analysis targeting genes involved in OHR metabolism. In addition, the competition of both dechlorinating populations for the substrate PCE is assessed by mixing them with different ratios and following their growth and activity. This should further help understanding the molecular basis of substrate affinity and specificity of the two RdhA enzymes present.