Copper oxidase and encapsulin shell protein in anammox bacteria reduces phenol toxicity from water

Abstract

The inhibition of phenol on anammox bacteria limits the application of anammox in the treatment of phenol-containing wastewaters. The molecular mechanism of how anammox bacteria resist phenol toxicity in wastewater remains unclear. In this study, copper oxidase (Cop) and encapsulin shell protein (cEnc) from anammox bacteria Candidatus Brocadia fulgida were found to assist bacteria to resist phenol stress. The Cop and its complex with cEnc (cEnc–Cop) expressed in vitro by molecular biology had laccase-like activities (1.39 U/mg and 0.79 U/mg, respectively). Combined with real-time quantitative polymerase chain reaction, both the Cop and cEnc gene expression levels were upregulated by stimulating anammox bacteria with phenol for a short time. It was also found that hydrazine synthase genes increased first and then decreased. These results indicated that cEnc–Cop relieved the inhibition of phenol to hydrazine synthase by degrading phenol, and consequently restored anammox activity. These findings will contribute to a deeper insight into the mechanism of how anammox bacteria respond to phenol and phenolic compound stress, and provide a theoretical reference for the application of anammox technology to phenol and phenolic compound-containing wastewater treatment.