Swette Center for Environmental Biotechnology, Biodesign Institute, Arizona State University, PO Box 875001, Tempe, AZ 85287-5701, USA.
Microb Cell Fact. 2012 Sep 13;11:128. doi: 10.1186/1475-2859-11-128.
Buffering to achieve pH control is crucial for successful trichloroethene (TCE) anaerobic bioremediation. Bicarbonate (HCO3-) is the natural buffer in groundwater and the buffer of choice in the laboratory and at contaminated sites undergoing biological treatment with organohalide respiring microorganisms. However, HCO3- also serves as the electron acceptor for hydrogenotrophic methanogens and hydrogenotrophic homoacetogens, two microbial groups competing with organohalide respirers for hydrogen (H2). We studied the effect of HCO3- as a buffering agent and the effect of HCO3--consuming reactions in a range of concentrations (2.5-30 mM) with an initial pH of 7.5 in H2-fed TCE reductively dechlorinating communities containing Dehalococcoides, hydrogenotrophic methanogens, and hydrogenotrophic homoacetogens.
Rate differences in TCE dechlorination were observed as a result of added varying HCO3- concentrations due to H2-fed electrons channeled towards methanogenesis and homoacetogenesis and pH increases (up to 8.7) from biological HCO3- consumption. Significantly faster dechlorination rates were noted at all HCO3- concentrations tested when the pH buffering was improved by providing 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as an additional buffer. Electron balances and quantitative PCR revealed that methanogenesis was the main electron sink when the initial HCO3- concentrations were 2.5 and 5 mM, while homoacetogenesis was the dominant process and sink when 10 and 30 mM HCO3- were provided initially.
Our study reveals that HCO3- is an important variable for bioremediation of chloroethenes as it has a prominent role as an electron acceptor for methanogenesis and homoacetogenesis. It also illustrates the changes in rates and extent of reductive dechlorination resulting from the combined effect of electron donor competition stimulated by HCO3- and the changes in pH exerted by methanogens and homoacetogens.
缓冲作用对于成功进行三氯乙烯（TCE）厌氧生物修复至关重要。碳酸氢盐（HCO3-）是地下水的天然缓冲剂，也是实验室和受生物处理影响的污染场地中选择的缓冲剂，这些污染场地正在使用有机卤化物呼吸微生物进行生物处理。然而，HCO3-也可作为氢营养型产甲烷菌和氢营养型同型乙酸菌的电子受体，这两种微生物群与有机卤化物呼吸菌竞争氢（H2）。我们研究了 HCO3-作为缓冲剂的作用以及在一系列浓度（2.5-30 mM）下 HCO3-消耗反应的作用，初始 pH 为 7.5，在含有 Dehalococcoides 的 H2 进料 TCE 还原脱氯群落中，存在氢营养型产甲烷菌和氢营养型同型乙酸菌。
由于添加了不同的 HCO3-浓度导致 H2 进料电子流向甲烷生成和同型乙酸生成以及生物 HCO3-消耗导致 pH 值升高（高达 8.7），因此观察到由于添加了不同的 HCO3-浓度而导致 TCE 脱氯速率存在差异。当通过提供 4-(2-羟乙基)-1-哌嗪乙磺酸（HEPES）作为额外缓冲剂来改善 pH 缓冲时，在所有测试的 HCO3-浓度下都观察到明显更快的脱氯速率。电子平衡和定量 PCR 表明，当初始 HCO3-浓度为 2.5 和 5 mM 时，甲烷生成是主要的电子汇，而当提供 10 和 30 mM HCO3-时，同型乙酸生成是主要的过程和汇。
我们的研究表明，HCO3-是氯代烯烃生物修复的一个重要变量，因为它作为甲烷生成和同型乙酸生成的电子受体具有重要作用。它还说明了由于 HCO3-刺激的电子供体竞争和产甲烷菌和同型乙酸菌引起的 pH 值变化的共同作用，导致还原脱氯的速率和程度发生变化。
