葡萄糖和麦芽糖碳源底物对粪产碱杆菌合成凝胶多糖的胞内代谢流影响

Effects of Glucose and Maltose Substrates on the Intracellular Metabolic Flux Distribution of Curdlan Polysaccharides Biosynthesis by Alcaligenes faecalis

麦芽糖和葡萄糖对粪产碱杆菌发酵合成凝胶多糖有着显著的影响,为了详细分析两种底物对凝胶多糖合成的影响机制,利用恒化培养实验及稳态碳平衡代谢分析,研究发现在稀释速率为0.1h-1时,利用麦芽糖和葡萄糖为碳源底物的条件下粪产碱杆菌的微观代谢途径通量有较大的差异。以麦芽糖为底物时凝胶多糖的摩尔得率为53.8%,比葡萄糖为碳源时的摩尔得率(36.9%)高出了45.8%以上。同时以麦芽糖为碳源时HMP途径的绝对代谢通量比葡萄糖时的通量提升了40%以上。这条途径通量的增加,提升了NADPH还原力供给速率,促进了依赖于还原力NADPH的凝胶多糖合成途径通量,提升了碳源底物向产物的摩尔转化速率。而且代谢流分析结果显示ED途径通量和能量提供也是影响粪产碱杆菌凝胶多糖合成效率的关键因素。麦芽糖作为碳源底物过程中维持的较低的残留葡萄糖浓度解除了高葡萄糖浓度条件下对凝胶多糖合成的抑制,能够实现更高通量的ATP能量提供效率,更加促进了凝胶多糖合成通量。

Maltose and glucose have significant effects on the production of curdlan by fermentation of Alcaligenes faecalis.The chemostat culture and steady-state carbon balanced metabolic flux analysis were applied to evaluate the effect of the substrates on curdlan biosynthesis in detail.Results demonstrated that the intracellular metabolism of A.faecalis were significantly different under the substrates of maltose and glucose as the carbon substrate at the dilution rate of 0.1h-1.The relative metabolic flux analysis showed the curdlan yield reached 53.8%under maltose source,which was more than 45.8%higher than that of glucose(36.9%).At the same time,the absolute metabolic flux of the HMP pathway increased more than 40%than that of glucose,and enhanced the supply rate of NADPH.The higher NADPH supply level promotes the flux ratio of curdlan biosynthesis,which depends on NADPH cofactors,and increases the molar conversion rate of curdlan from carbon source substrate.Moreover,the metabolic flux distribution results also showed that the ED pathway distribution and energy supply are also the key factors affecting the curdlan biosynthesis efficiency of A.faecalis.The lower residual glucose concentration with maltose as carbon source substrate could relieve the inhibition on curdlan synthesis,and could achieve higher flux ratio of ATP supply for promoting the curdlan biosynthesis efficiency.