Hormesis and synergistic effects of disinfectants chloroxylenol and benzethonium chloride on highly efficient heterotrophic nitrification-aerobic denitrification functional strain: From performance to mechanism.

The heterotrophic nitrification-aerobic denitrification (HNAD) strain Exiguobacterium H1 (H1) was isolated in this study. The changes in nitrogen metabolism functions of H1 strain were discussed in presence of disinfectants chloroxylenol (PCMX) and benzethonium chloride (BEC) alone and combined pollution (PCMX+BEC). The H1 strain could use NH4+-N, NO2--N and NO3--N as nitrogen sources and had good nitrogen removal performance under conditions of C/N ratio 25, pH 5-8, 25-35 oC and sodium acetate as carbon. PCMX and BEC alone exhibited hormesis effects on H1 strain which promoted the growth of H1 strain at low concentrations but inhibited it at high concentrations, and combined pollution showed synergistic inhibitory on H1 strain. H1 strain owned a full nitrogen metabolic pathway according to functional genes quantification. PCMX encouraged nitrification process of H1, while BEC and combined pollution mostly blocked nitrogen removal. PCMX, but not BEC, mainly led to the enrichment of resistance genes. These findings will aid in systematic assessment of contaminant tolerance characteristics of HNAD strain and its application prospects.