Transcriptomics Uncovers the Response of Anammox Bacteria to Dissolved Oxygen Inhibition and the Subsequent Recovery Mechanism

Understanding the recovery of anaerobic
ammonium-oxidizing (anammox)
bacteria after inhibition by dissolved oxygen (DO) is critical for
the successful applications of anammox-based processes. Therefore,
the effects of oxygen exposure (2 mg L–1 DO for 90 min) and subsequent recovery treatments [N2 purging or nano zero-valent iron (nZVI) addition] on the activity
and gene expression in a Kuenenia stuttgartiensis enrichment culture were examined. Combining the self-organizing
map clustering and enrichment analysis, we proposed the oxidative
stress response of anammox bacteria based on the existing concepts
of oxidative stress in microbes: the DO exposure triggered a stringent
response in K. stuttgartiensis, which
downregulated the transcription levels of genes involved in the central
metabolism and diverted energy to a flagellar assembly and metal transport
modules; these changes possibly promoted survival during the inhibition
of anammox activity. According to the cotranscription with central
catabolism genes, putative reactive oxygen species (ROS) scavenger
genes (kat and sod) were presumed
to detoxify the anammox intermediates rather than ROS. In addition,
both activity and mRNA profiles with appropriate amount of nZVI addition
(5 and 25 mg L–1) were close to that of control,
which proved the effectiveness of nZVI addition in anammox recovery.
These results would be relevant to the physio-biochemistry development
of anammox bacteria and further enhancement of nitrogen removal in
wastewater treatment.

阐明溶解氧（dissolved oxygen，DO）抑制后厌氧铵氧化（anaerobic ammonium-oxidizing，anammox）细菌的恢复过程，对基于anammox的工艺规模化应用具有关键意义。为此，本研究考察了氧暴露（2 mg·L⁻¹ DO，持续90 min）及后续恢复处理——氮气吹扫或添加纳米零价铁（nano zero-valent iron，nZVI）——对斯图加特库嫩菌（Kuenenia stuttgartiensis）富集培养物的活性与基因表达的影响。本研究结合自组织映射聚类（self-organizing map clustering）与富集分析，基于微生物氧化应激的既有理论，提出了anammox细菌的氧化应激响应机制：DO暴露会触发斯图加特库嫩菌产生严谨反应（stringent response），下调中心代谢相关基因的转录水平，并将能量分配至鞭毛组装与金属转运模块；此类变化或可帮助细菌在anammox活性受抑的状态下维持存活。通过与中心分解代谢基因的共转录分析，推定的活性氧（reactive oxygen species，ROS）清除基因（kat与sod）的功能或为解毒anammox中间产物，而非直接清除ROS。此外，添加适量nZVI（5与25 mg·L⁻¹）后的细菌活性与mRNA转录谱均与对照组相近，证实了nZVI添加用于促进anammox系统恢复的有效性。本研究结果可为anammox细菌的生理生化特性研究提供参考，并助力污水处理系统脱氮效能的进一步提升。