Effects of Different Ratios of Carbon and Nitrogen Sources on the Growth of Hyphomicrobium denitrificans FJNU-R8 and PQQ Synthesis

In order to improve the ability of Hyphomicrobium denitrificans FJNU-R8 to produce PQQ, FJNU-R8 was used as the starting strain, and the effects of different ratios of carbon and nitrogen sources on its growth and PQQ synthesis were explored. Based on exploring the effects of four sole carbon sources and four sole nitrogen sources on the strain growth and PQQ synthesis, the effects of different ratios and different concentrations of composite carbon source (methanol : glycerol) / composite nitrogen source (protein peptone: ammonium sulfate) on the strain growth and PQQ yield were further studied. The results showed that: when methanol was used as the sole carbon source, the OD₆₅₀ was only 4.4, but the PQQ yield was 43 mg·L^-1. When glycerol was used as the sole carbon source, the OD₆₅₀ could reach 9.8, but there was no PQQ yield. When ammonium sulfate was used as the sole nitrogen source, the OD₆₅₀ was only 4.2, but the PQQ yield was 30 mg·L^-1, and when protein peptone was used as the sole nitrogen source, the OD₆₅₀ could reach 7.7, but there was no PQQ yield. Different ratios of composite carbon source could improve the OD₆₅₀, and the greater the proportion of glycerol, the higher the final OD₆₅₀, but the PQQ yield was very low. Different ratios of composite nitrogen source could improve the growth rate, and the PQQ yield was 65 mg·L^-1 when the ratio of protein peptone to ammonium sulfate was 40∶60. The higher the concentration of composite carbon source (the ratio of methanol to glycerol was 20∶80), the higher the final OD₆₅₀, but the lower the PQQ yield. When the concentration of composite nitrogen source (the ratio of protein peptone to ammonium sulfate was 40∶60) was higher than 1 g·L^-1, there was no significant change in OD₆₅₀ and PQQ yield. The final OD₆₅₀ was about 7.5, and the PQQ yield was about 45 mg·L^-1. The results showed that the composite carbon source could increase OD₆₅₀, and the composite nitrogen source could increase the yield of PQQ, which could provide a theoretical basis for the subsequent selection of carbon and nitrogen sources for the high-yielding PQQ.