Production of medium-chain carboxylic acids (MCCAs) by chain elongation (CE) presents a competitive alternative to conventional products of methane in anaerobic digestion treating organic waste streams, considering energy recovery, economic, and environmental profits. However, the system stability and performance largely rely on the selective suppression of methanogens while stimulation of CE bacteria. Commercial inhibitors such as 2-bromoethanesulfonic sodium (BES) was shown to be effective, but controversial conclusions exist on its inhibition characteristics and the inhibition mechanism remains unclear. Therefore, this study systematically investigated the responses of methanogenesis in granular sludge to various BES levels, focusing on methane production, methanogenic pathway, dynamic populations, electron transport and energy metabolism. Results showed that compared with the control, 3.0 g/L BES was sufficient to induce a 72.9% reduced level on accumulative methane production by the end of 4 cycles (28 days), which was likely to be attributed to the significantly suppressed metabolic pathways and intracellular regulations. Specifically, BES suppressed the electron transport via unproper electron carriers and reduced electron amount as indicated by the decreased level of enzymes and genes involved such as coenzyme F, CO dehydrogenase and NADH:ubiquinone reductase (H-translocating). Moreover, BES regulated the intracellular energy metabolism, leading to the impeded ATP synthesis but enhanced ATP consumption as evidenced by the variations on the activity or abundance of acetate kinase, A1Ao-ATP synthase, nitrogenase and ATP citrate synthase. Additionally, BES enriched hydrogenotrophic methanogenesis over acetoclastic one as supported by variations on the archaeal community structures and regulations of differentially expressed genes involved. Moreover, BES also reduced the contents of both protein and carbohydrate in extracellular polymeric substances (EPS). This study is expected to enhance understanding of BES contribution to methanogenesis inhibition but MCCAs production in CE bioreactors.

中文翻译：

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2-溴乙磺酸钠对产甲烷作用的影响：产甲烷菌代谢和群落结构


考虑到能源回收、经济和环境利润，通过链延长 (CE) 生产中链羧酸 (MCCA) 是厌氧消化处理有机废物流中传统甲烷产品的一种有竞争力的替代品。然而，系统的稳定性和性能很大程度上依赖于对产甲烷菌的选择性抑制，同时对CE细菌的刺激。商业抑制剂如2-溴乙磺酸钠（BES）被证明是有效的，但其抑制特性存在争议，且抑制机制仍不清楚。因此，本研究系统地研究了颗粒污泥中产甲烷作用对不同BES水平的响应，重点关注甲烷产生、产甲烷途径、动态种群、电子传递和能量代谢。结果表明，与对照相比，3.0 g/L BES 足以在 4 个周期结束时（28 天）使累计甲烷产量降低 72.9%，这可能是由于代谢途径受到显着抑制，细胞内调节。具体来说，BES 通过不适当的电子载体抑制电子传输，并减少电子量，这可以通过辅酶 F、CO 脱氢酶和 NADH：泛醌还原酶（H 转位）等相关酶和基因水平的降低来表明。此外，BES 调节细胞内能量代谢，导致 ATP 合成受阻，但 ATP 消耗增加，乙酸激酶、A1Ao-ATP 合酶、固氮酶和 ATP 柠檬酸合酶的活性或丰度变化证明了这一点。 此外，BES 比乙酰分解产甲烷作用更富集氢营养产甲烷作用，这得到了古菌群落结构的变化和所涉及的差异表达基因的调节的支持。此外，BES还降低了细胞外聚合物（EPS）中蛋白质和碳水化合物的含量。这项研究预计将加深对 BES 对 CE 生物反应器中产甲烷抑制和 MCCA 生产的贡献的理解。