The roles of methanogens and acetogens in dechlorination of trichloroethene using different electron donors
2015
Wen, Li-Lian | Zhang, Yin | Pan, Ya-Wei | Wu, Wen-Qi | Meng, Shao-Hua | Zhou, Chen | Tang, Youneng | Zheng, Ping | Zhao, He-Ping
We evaluated the effects of methanogens and acetogens on the function and structure of microbial communities doing reductive dechlorination of trichloroethene (TCE) by adding four distinct electron donors: lactate, a fermentable organic; acetate, a non-fermentable organic; methanol, a fermentable 1-C (carbon) organic; and hydrogen gas (H₂), the direct electron donor for reductive dechlorination by Dehalococcoides. The fermentable electron donors had faster dechlorination rates, more complete dechlorination, and higher bacterial abundances than the non-fermentable electron donors during short-term tests. Phylotypes of Dehalococcoides were relatively abundant (≥9 %) for the cultures fed with fermentable electron donors but accounted for only ~1–2 % of the reads for the cultures fed by the non-fermentable electron donors. Routing electrons to methanogenesis and a low ratio of Dehalococcoides/methanogenesis (Dhc/mcrA) were associated with slow and incomplete reductive dechlorination with methanol and H₂. When fermentable substrates were applied as electron donors, a Dhc/mcrA ratio ≥6.4 was essential to achieve fast and complete dechlorination of TCE to ethene. When methanogenesis was suppressed using 2-bromoethanesulfonate (BES), achieving complete dechlorination of TCE to ethane required a minimum abundance of the mcrA gene. Methanobacterium appeared to be important for maintaining a high dechlorination rate, probably by providing Dehalococcoides with cofactors other than vitamin B₁₂. Furthermore, the presence of homoacetogens also was important to maintain a high dechlorination rate, because they provided acetate as Dehalococcoides’s obligatory carbon source and possibly cofactors.
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