Okabe Satoshi, Ye Shaoyu, Lan Xi, Nukada Keishi, Zhang Haozhe, Kobayashi Kanae, Oshiki Mamoru
Department of Environmental Engineering, Faculty of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, Hokkaido, 060-8628, Japan.
Super-cutting-edge Grand and Advanced Research (SUGAR) Program, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa, 237-0061, Japan.
ISME Commun. 2023 May 3;3(1):45. doi: 10.1038/s43705-023-00251-7.
Oxygen is a key regulatory factor of anaerobic ammonium oxidation (anammox). Although the inhibitory effect of oxygen is evident, a wide range of oxygen sensitivities of anammox bacteria have been reported so far, which makes it difficult to model the marine nitrogen loss and design anammox-based technologies. Here, oxygen tolerance and detoxification mechanisms of four genera of anammox bacteria; one marine species ("Ca. Scalindua sp.") and four freshwater anammox species ("Ca. Brocadia sinica", "Ca. Brocadia sapporoensis", "Ca. Jettenia caeni", and "Ca. Kuenenia stuttgartiensis") were determined and then related to the activities of anti-oxidative enzymes. Highly enriched planktonic anammox cells were exposed to various levels of oxygen, and oxygen inhibition kinetics (50% inhibitory concentration (IC) and upper O limits (DO) of anammox activity) were quantitatively determined. A marine anammox species, "Ca. Scalindua sp.", exhibited much higher oxygen tolerance capability (IC = 18.0 µM and DO = 51.6 µM) than freshwater species (IC = 2.7-4.2 µM and DO = 10.9-26.6 µM). The upper DO limit of "Ca. Scalindua sp." was much higher than the values reported so far (~20 µM). Furthermore, the oxygen inhibition was reversible even after exposed to ambient air for 12-24 h. The comparative genome analysis confirmed that all anammox species commonly possess the genes considered to function for reduction of O, superoxide anion (O), and HO. However, the superoxide reductase (Sor)-peroxidase dependent detoxification system alone may not be sufficient for cell survival under microaerobic conditions. Despite the fact that anaerobes normally possess no or little superoxide dismutase (Sod) or catalase (Cat), only Scalindua exhibited high Sod activity of 22.6 ± 1.9 U/mg-protein with moderate Cat activity of 1.6 ± 0.7 U/mg-protein, which was consistent with the genome sequence analysis. This Sod-Cat dependent detoxification system could be responsible for the higher O tolerance of Scalindua than other freshwater anammox species lacking the Sod activity.
氧气是厌氧氨氧化（anammox）的关键调节因子。尽管氧气的抑制作用很明显，但迄今为止已报道厌氧氨氧化细菌对氧气的敏感性范围很广，这使得难以对海洋氮损失进行建模以及设计基于厌氧氨氧化的技术。在此，测定了4个厌氧氨氧化细菌属（1个海洋物种“Ca. Scalindua sp.”和4个淡水厌氧氨氧化物种“Ca. Brocadia sinica”、“Ca. Brocadia sapporoensis”、“Ca. Jettenia caeni”和“Ca. Kuenenia stuttgartiensis”）的氧气耐受性和解毒机制，然后将其与抗氧化酶的活性相关联。将高度富集的浮游厌氧氨氧化细胞暴露于不同水平的氧气中，并定量测定氧气抑制动力学（厌氧氨氧化活性的50%抑制浓度（IC）和氧气上限（DO））。一种海洋厌氧氨氧化物种“Ca. Scalindua sp.”表现出比淡水物种（IC = 2.7 - 4.2 μM，DO = 10.9 - 26.6 μM）高得多的氧气耐受能力（IC = 18.0 μM，DO = 51.6 μM）。“Ca. Scalindua sp.”的DO上限远高于迄今为止报道的值（约20 μM）。此外，即使暴露于环境空气中12 - 24小时后，氧气抑制也是可逆的。比较基因组分析证实，所有厌氧氨氧化物种通常都拥有被认为具有还原O、超氧阴离子（O）和HO功能的基因。然而，仅超氧化物还原酶（Sor）-过氧化物酶依赖性解毒系统可能不足以在微需氧条件下使细胞存活。尽管厌氧菌通常不具有或仅具有很少的超氧化物歧化酶（Sod）或过氧化氢酶（Cat），但只有Scalindua表现出22.6±1.9 U/mg蛋白的高Sod活性和1.6±0.7 U/mg蛋白的适度Cat活性，这与基因组序列分析一致。这种Sod - Cat依赖性解毒系统可能是Scalindua比其他缺乏Sod活性的淡水厌氧氨氧化物种具有更高O耐受性的原因。
