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.