Kato Souichiro, Sasaki Konomi, Watanabe Kazuya, Yumoto Isao, Kamagata Yoichi
Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST).
Microbes Environ. 2014;29(2):162-7. doi: 10.1264/jsme2.me14021. Epub 2014 Jun 10.
The inhibitory effects of ammonia on two different degradation pathways of methanogenic acetate were evaluated using a pure culture (Methanosaeta thermophila strain PT) and defined co-culture (Methanothermobacter thermautotrophicus strain TM and Thermacetogenium phaeum strain PB), which represented aceticlastic and syntrophic methanogenesis, respectively. Growth experiments with high concentrations of ammonia clearly demonstrated that sensitivity to ammonia stress was markedly higher in M. thermophila PT than in the syntrophic co-culture. M. thermophila PT also exhibited higher sensitivity to high pH stress, which indicated that an inability to maintain pH homeostasis is an underlying cause of ammonia inhibition. Methanogenesis was inhibited in the resting cells of M. thermophila PT with moderate concentrations of ammonia, suggesting that the inhibition of enzymes involved in methanogenesis may be one of the major factors responsible for ammonia toxicity. Transcriptomic analysis revealed a broad range of disturbances in M. thermophila PT cells under ammonia stress conditions, including protein denaturation, oxidative stress, and intracellular cation imbalances. The results of the present study clearly demonstrated that syntrophic acetate degradation dominated over aceticlastic methanogenesis under ammonia stress conditions, which is consistent with the findings of previous studies on complex microbial community systems. Our results also imply that the co-existence of multiple metabolic pathways and their different sensitivities to stress factors confer resiliency on methanogenic processes.
利用纯培养物（嗜热产甲烷丝菌PT菌株）和特定共培养物（嗜热自养甲烷杆菌TM菌株和嗜热产乙酸菌PB菌株）评估了氨对产甲烷乙酸盐两种不同降解途径的抑制作用，这两种培养物分别代表乙酸裂解产甲烷和互营产甲烷。高浓度氨的生长实验清楚地表明，嗜热产甲烷丝菌PT对氨胁迫的敏感性明显高于互营共培养物。嗜热产甲烷丝菌PT对高pH胁迫也表现出更高的敏感性，这表明无法维持pH稳态是氨抑制的一个潜在原因。中等浓度的氨抑制了嗜热产甲烷丝菌PT静息细胞中的产甲烷作用，这表明参与产甲烷作用的酶的抑制可能是氨毒性的主要因素之一。转录组分析揭示了在氨胁迫条件下嗜热产甲烷丝菌PT细胞中存在广泛的干扰，包括蛋白质变性、氧化应激和细胞内阳离子失衡。本研究结果清楚地表明，在氨胁迫条件下，互营乙酸盐降解比乙酸裂解产甲烷占主导地位，这与先前关于复杂微生物群落系统的研究结果一致。我们的结果还表明，多种代谢途径的共存及其对胁迫因子的不同敏感性赋予了产甲烷过程弹性。
