Abstract: Strain with strong capacity of ammoxidation screened by repeated enrichment and separation methods from activated sludge, was collected from sewage treatment plant in China university of mining and technology. Lithium chloride and ethidium bromide mutagenesis methods of ammonia-oxidizing bacteria protoplast were used to breed mutant strain with strong capacity of ammoxidation. The relationship between concentrations of chemical mutagens and capacity of ammoxidation were researched. The results showed that regenerated colony number of protoplast decreased with increased lithium chloride or ethidium bromide mutagenic concentration. After culvation of 1 L simulation sewage medium, the mutagenic strain LC002, mutated by 2.5 mg/mL lithium chloride, still had better capacity of ammoxidation with 86.89% removal rate of ammonia nitrogen. The mutagenic strain EB003, mutated by 2 μg/mL ethidium bromide, also had better capacity of ammoxidation with 85.67% removal rate of ammonia nitrogen. Protoplast mutagenisis was an effective breeding method to breed excellent ammonia-oxidizing bacteria for further application.

Key words: Ammonia-oxidizing bacteria, Protoplast, Mutagenesis, Lithium chloride, Ethidium bromide