Anoxygenic phototrophic bacteria(APB)played an important role in nitrogen cycle,it is capable of conversion and utilization of inorganic nitrogen distributed in terrestrial and marine environment.However,little is known about nitrification of APB as well as capable of growth on nitrite as sole nitrogen source.In the present study,we discovered that Marichromatium gracile YL28 could transform ammonia into nitrite and nitrate when strain YL28 was grown on ammonium as the sole nitrogen source under anaerobic light.It indicating that APB possess anaerobic nitrification.Although YL28 was not grown well under aerobic light conditions,the continuity accumulation of nitrate and nitrite due to the denitrification inhibition was detected.Interestingly,this strain was capable of growing on nitrite as the sole nitrogen source under anaerobic light and anaerobic dark conditions.These results suggested that Marichromatium gracile YL28 was capable of transforming ammonia into nitrite and nitrate under anaerobic light condition,and growing on nitrite as sole nitrogen source.This study presented the evidence on anaerobic nitrification of APB for the first time,and promoted our understandings of nitrogen metabolism in APB and its role in geochemical cycling.It helpful to control the environment pollution.