Salinity Tolerance and Osmoadaptation Strategies in Four Genera of Anammox Bacteria: Brocadia, Jettenia, Kuenenia, and Scalindua

The salinity tolerance and osmoadaptation strategies in four phylogenetically distant anammox species, Brocadia, Jettenia, Kuenenia, and Scalindua, were investigated by using highly enriched cell cultures. The first-emerged “Ca. Scalindua sp.” showed optimum growth at 1.5–3% salinity and was tolerant to ∼10% salinity (a slight halophile). The second-emerged “Ca. Kuenenia stuttgartiensis” was tolerant to ∼6% salinity with optimum growth at 0.25–1.5% (a halotolerant). These early-emerged “Ca. Scalindua sp.” and ″Ca. K. stuttgartiensis” rapidly accumulated K+ ions and simultaneously synthesized glutamate as a counterion. Subsequently, part of the glutamate was replaced by trehalose. In contrast, the late-emerged “Ca. B. sinica” and “Ca. J. caeni” were unable to accumulate sufficient amounts of K+glutamate and trehalose, resulting in a significant decrease in activity even at 1–2% salinity (nonhalophiles). In addition, the external addition of glutamate may increase anammox activity at high salinity. The species-dependent salinity tolerance and osmoadaptation strategies were consistent with the genetic potential required for the biosynthesis and transport of these osmolytes and the evolutionary history of anammox bacteria: Scalindua first emerged in marine environments and then Kuenenia and other two species gradually expanded their habitat to estuaries, freshwater, and terrestrial environments, while Brocadia and Jettenia likely lost their ability to accumulate K+glutamate.

本研究采用高度富集的细胞培养体系，对4个系统发育疏远的厌氧氨氧化（anammox）菌种——布罗卡德氏菌属（Brocadia）、杰特尼亚菌属（Jettenia）、库嫩尼亚菌属（Kuenenia）以及斯氏厌氧氨氧化菌属（Scalindua）的耐盐特性与渗透适应策略展开了探究。首次演化出现的候选（Candidatus）斯氏厌氧氨氧化菌属菌种（"Ca. Scalindua sp."）在1.5%~3%的盐度条件下生长最优，可耐受约10%的盐度，属于轻度嗜盐菌。随后演化出现的候选（Candidatus）斯图加特库嫩尼亚菌（"Ca. Kuenenia stuttgartiensis"）可耐受约6%的盐度，最优生长盐度为0.25%~1.5%，属于耐盐菌。这两类早期演化出现的菌种可快速积累钾离子（K+），并同步合成谷氨酸作为反离子；随后部分谷氨酸会被海藻糖（trehalose）替代。与之相反，后期演化出现的候选（Candidatus）中华布罗卡德氏菌（"Ca. B. sinica"）与候选（Candidatus）污泥杰特尼亚菌（"Ca. J. caeni"）无法积累足量的钾离子-谷氨酸复合物与海藻糖，即便在1%~2%的盐度条件下，其活性也会显著下降，属于非嗜盐菌。此外，在高盐环境中外源添加谷氨酸可提升厌氧氨氧化活性。菌种特异性的耐盐特性与渗透适应策略，与这些渗透调节物质（osmolytes）的生物合成及转运所需的遗传潜力，以及厌氧氨氧化细菌的演化历史高度吻合：斯氏厌氧氨氧化菌属最初起源于海洋环境，随后库嫩尼亚菌属与另外两个菌种逐步将栖息范围拓展至河口、淡水及陆地环境；而布罗卡德氏菌属与杰特尼亚菌属则可能丧失了积累钾离子-谷氨酸复合物的能力。