Division of Environmental Engineering, Faculty of Engineering, Hokkaido University.
Microbes Environ. 2020;35(4). doi: 10.1264/jsme2.ME20086.
The activity of anaerobic ammonia-oxidizing (anammox) bacteria is considered to depend on cell density; however, this has not yet been confirmed due to the fastidious nature of anammox bacteria (e.g., slow growth, oxygen sensitivity, and rigid aggregate formation). In the present study, the cell density-dependent occurrence of anammox activity (N gas production rate) was investigated using planktonic enrichment cultures of Candidatus Brocadia sinica. This activity was detectable when the density of cells was higher than 10 cells mL and became stronger with increases in cell density. At the cell densities, the transcription of the BROSI_A1042 and BROSI_A3652 genes, which are potentially involved in the biosynthesis and reception of N-acyl homoserine lactone (AHL), was detectable in Brocadia sinica cells. The presence of AHL molecules in the MBR culture of B. sinica was confirmed by an AHL reporter assay and gas chromatography mass spectrometry analysis. The exogenous addition of the MBR culture extract and AHL molecules (a cocktail of C, C, C, and C-homoserine lactones) increased the specific N production rate of B. sinica. These results suggest that the specific anammox activity of B. sinica is regulated by AHL-mediated quorum sensing.
厌氧氨氧化（anammox）细菌的活性被认为取决于细胞密度；然而，由于 anammox 细菌的苛刻性质（例如，生长缓慢、对氧气敏感和刚性聚集体形成），这尚未得到证实。在本研究中，使用 Candidatus Brocadia sinica 的浮游生物富集培养物来研究与细胞密度相关的厌氧氨氧化活性（N 气体产生速率）。当细胞密度高于 10cellsmL 时，可以检测到这种活性，并且随着细胞密度的增加而增强。在这些细胞密度下，Brocadia sinica 细胞中潜在参与 N-酰基高丝氨酸内酯（AHL）生物合成和接收的 BROSI_A1042 和 BROSI_A3652 基因的转录是可检测的。通过 AHL 报告基因测定和气相色谱-质谱分析证实了 MBR 培养物中 AHL 分子的存在。MBR 培养物提取物和 AHL 分子（C、C、C 和 C-高丝氨酸内酯的混合物）的外源添加增加了 Brocadia sinica 的特定 N 生产速率。这些结果表明，Brocadia sinica 的特定厌氧氨氧化活性受 AHL 介导的群体感应调节。
