天然酵母菌利用海藻酸生成乙醇的代谢机理研究

天然酵母菌利用褐藻生成乙醇可以规避传统生物乙醇生产方法的不足，正在成为能源领域关注的热点之一，但是其代谢机理尚不明确。考察了不同碳源对季也蒙酵母（Meyerozyma guilliermondii）发酵生产乙醇的影响；通过高效液相色谱法（HPLC）和气相色谱法（GC）测定了海藻酸代谢过程中重要中间产物含量的动态变化。结果表明：季也蒙酵母可以直接利用甘露糖醛酸和古洛糖醛酸这两种单体进行乙醇发酵；在发酵过程中，中间产物丙酮酸、3-磷酸甘油醛和乙醛的浓度均呈现先增大后减小的趋势，但3-磷酸甘油醛的浓度变化较小。建立了海藻酸的代谢途径模型，并通过乙二胺四乙酸（EDTA）添加试验和镁离子浓度控制试验初步验证了该模型，推测海藻酸的代谢途径为：酵母菌产生胞外海藻酸裂解酶，将海藻酸裂解成寡聚海藻酸，随后进一步降解为低聚体；进入酵母菌细胞后，低聚体转化为糖醛酸单体等前体物质，随后转化为3-磷酸甘油醛、丙酮酸等中间产物，然后在丙酮酸脱羧酶及乙醇脱氢酶的作用下，最终生成乙醇。

Metabolic mechanism of ethanol production from alginate using natural yeast

The treatment of brown algae with natural yeast to generate ethanol can circumvent the shortcomings of traditional bioethanol production methods and is becoming one of the hotspots in the energy field. However its metabolic mechanism is still unclear. The effects of different carbon sources on ethanol production by Meyerozyma guilliermondii were investigated. The dynamic changes in the content of important intermediates in the process of alginate metabolism were determined by high performance liquid chromatography (HPLC) and gas chromatography (GC). The results showed that M. guilliermondii could directly use two monomers, mannuronic acid and guluronic acid, for ethanol fermentation. During the fermentation process, the concentrations of intermediate products pyruvate, glyceraldehyde 3-phosphate and acetaldehyde all showed an initial increase followed by a decrease, but the concentration of glyceraldehyde 3-phosphate varied less. A metabolic pathway model for alginic acid was established, and the model was preliminarily verified by EDTA addition tests and magnesium ion concentration control tests. We propose that the metabolic pathway of alginate is as follows: yeast produces extracellular alginate lyase, and alginate is decomposed into oligomeric alginate species, which are further degraded into oligomers. After entering yeast cells, the oligomers were converted into precursors such as uronic acid monomer, and then converted into intermediate products such as glyceraldehyde 3-phosphate and pyruvate. Finally ethanol was generated under the action of pyruvate decarboxylase and ethanol dehydrogenase.