Development of a defined three-strain nitrifying microbial community for ammonification and nitrification under organic nitrogen conditions

A simplified synthetic nitrifying microbial community capable of sequential ammonification and nitrification under organic conditions was constructed using three defined strains: Bacillus badius NBRC 15713, Nitrosomonas europaea NBRC 14298, and Nitrobacter winogradskyi NBRC 14297. This co-culture achieved complete ammonification and nitrification under selected organic nitrogen conditions, with NO₃⁻–N accumulation of approximately 56 mg–N/L and no residual NO₂⁻–N detected. RT-qPCR analysis showed that changes in the relative abundance of N. europaea and N. winogradskyi were associated with changes in inorganic nitrogen concentrations during cultivation, indicating that the co-culture supported the growth and activity of nitrifying bacteria despite the presence of organic compounds that inhibit nitrification. This defined three-strain community provides a reproducible model for studying sequential microbial nitrogen conversion under organic nitrogen conditions.