Effects of culture conditions on denitrification activity by Magnetospirillum gryphiswaldense strain MSR-1

Abstract

The application of denitrification function of Magnetospirillum gryphiswaldense strain MSR-1 has not received attention. Here, we studied the effects of different culture conditions, including carbon (C) and nitrogen (N) sources, C/N ratio, iron source species and addition, initial pH, and temperature on the growth, magnetic production, and denitrification activity and application potential of MSR-1 under anoxic and nutrient environments similar to that of urban domestic sewage. Sodium lactate remains the best carbon source for denitrification by MSR-1, although acetic acid is also promising. Nitrate is the best nitrogen source, where addition and the ratio to nitrite should be >3 mM and 1, respectively. At C/N between 3 and 7, initial pH between 6.5 and 7.5, and culture temperature from 25 to 35 °C, nitrate content (84 mg N/L) decreased to the lowest value in 24 h, concomitant with the lowest residual nitrite. A maximum nitrate removal rate of 88.22 % was observed in 16 h by the optimization of response surface methodology with C/N = 5.13, initial pH = 6.83, and culture temperature = 30.3 °C. MSR-1 effectively removed nitrate, with the advantage of a low C/N demand; furthermore, optimal pH and temperature for denitrification are similar to those used in the sewage biological treatment system. Here, the consistency between optimal denitrification conditions of MSR-1 and actual wastewater conditions was considered for the first time, demonstrating the application potential of MSR-1 for wastewater denitrification and providing a theoretical basis for the application of the strain in wastewater treatment.