铵离子对必特螺旋霉素组分生物合成的调控作用

通过考察铵离子浓度对必特螺旋霉素组分的影响,证实低浓度铵离子的培养条件可以有效提高必特螺旋霉素中异戊酰螺旋霉素Ⅲ的比例。在此基础上进一步测定了高铵(62·5mmol/L)和低铵(2·5mmol/L)培养条件下的糖、铵离子、相关有机酸、缬氨酸脱氢酶酶活等中间代谢数据,结果表明高浓度铵离子培养条件下,必特螺旋霉素产生菌中亮氨酸分解代谢途径的关键酶——缬氨酸脱氢酶的活性低于低铵对照试验,造成异戊酰螺旋霉素合成过程中酰基转移反应的底物——异戊酰CoA的相对不足,从而导致异戊酰螺旋霉素组分的降低。大幅度降低铵离子浓度至2·5mmol/L,使异戊酰螺旋霉素Ⅲ的比例从5·43%提高至28·59%。但氮源的不足影响了必特螺旋霉素的产量,低铵条件下的效价为107μg/mL,相对高铵条件下降了14·4%。在低铵培养条件的基础上添加亮氨酸,可以进一步改善必特螺旋霉素的组分,异戊酰螺旋霉素Ⅲ的比例增至37·84%。

Effects of ammonium on components of biotechspiramycin

The effects of ammonium ion on the synthesis of biotechspiramycin were investigated. It was proved that the percentage of isovalerylspiramycin III was greatly enhanced in the medium with low concentration of ammonium ion. By greatly reducing ammonium ion concentration in the medium from 62.5mmol/L to 2.5mmol/L, the percentage of isovalerylspiramycin III increased from 5.43% to 28.59% . However, the titer of biotechspiramycin decreased to 107microg/mL in the medium with low concentration of ammonium ion, which was 14.4% lower than that in the medium with high concentration of ammonium ion, due to lack of nitrogen source. The results also showed that the activity of valine dehydrogenase, the key enzyme of leucine catabolic pathway, in the fermentation with high concentration of ammonium ion was lower than that with low ammonium ion concentration. This would lead to the limitation of isovaleryl-CoA, which is the substrate of isovaleryl transfer reaction, and then the decline of percentage of isovalerylspiramycin. The percentage of isovalerylspiramycin III further increased to 37.84% by addition of 0.3mg/mL leucine to the fermentation broth at 36h cultivation.