Metabolic fluxes in chemostat cultures of Schizosaccharomyces pombe grown on mixtures of glucose and ethanol
Metabolic fluxes in chemostat cultures of Schizosaccharomyces pombe grown on mixtures of glucose and ethanol
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DOI：
10.1099/13500872-142-6-1399
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发表时间：
1996-06-01
期刊：
影响因子：
--
通讯作者：
Pronk, JT
中科院分区：
文献类型：
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作者：
deJongGubbels, P;vanDijken, JP;Pronk, JT
研究了pombe裂殖酵母CBS 356在好氧恒温培养条件下同时利用葡萄糖和乙醇的情况。在葡萄糖限制培养中，呼吸发酵代谢发生在0.16h(-1)以上的生长速率。虽然Sch.庞贝缺乏一个功能性的乙醛酸循环，因此不能利用乙醇作为唯一的碳源，乙醇被葡萄糖限制的恒化器培养共同消耗。结果，生物量产量增加了，但没有达到理论值[0.92g生物量(g葡萄糖)(-1)]，如果从葡萄糖产生的乙酰辅酶A全部由乙醇合成的话。当混合饲料中乙醇占基质碳的30%以上时，乙醇未得到充分利用。在饲料中乙醇含量饱和的混合底物培养中，乙醇消耗导致的生物量产量在低稀释率时最高。这并不是因为乙醇在低增长率下的比消耗率增加；相反，在低稀释率下较长的停留时间允许SCH。为了利用更大比例的可用乙醇，其中一部分被氧化成乙酸酯，在任何培养物的无细胞提取物中都没有检测到糖异生和乙醛酸循环酶的活性。乙醛脱氢酶和乙酰辅酶A合成酶活性较低，与体内乙酸乙酯活化乙酰辅酶A的速率相同。结果表明，乙醇是SCH较差的底物。庞贝，甚至作为一种辅助能源。
Simultaneous utilization of glucose and ethanol by the yeast Schizosaccharomyces pombe CBS 356 was studied in aerobic chemostat cultures. In glucose-limited cultures, respirofermentative metabolism occurred at growth rates above 0.16 h(-1). Although Sch. pombe lacks a functional glyoxylate cycle and therefore cannot utilize ethanol as a sole carbon source, ethanol was co-consumed by glucose-limited chemostat cultures. As a result, biomass yields increased, but not up to the theoretical value [0.92 g biomass (g glucose)(-1)] expected if all of the acetyl-CoA produced from glucose was instead synthesized from ethanol. When ethanol accounted for more than 30% of the substrate carbon in the mixed feed, it was incompletely utilized. In mixed-substrate cultures with a saturating ethanol fraction in the feed, the increase of the biomass yield as a result of ethanol consumption was highest at low dilution rates. This was not due to an increased specific rate of ethanol consumption at low growth rates; rather, the longer residence times at low dilution rates allowed Sch. pombe to utilize a larger fraction of the available ethanol, part of which was oxidized to acetate, Activities of gluconeogenic and glyoxylate-cycle enzymes were not detected in cell-free extracts of any of the cultures. Activities of acetaldehyde dehydrogenase and acetyl-CoA synthetase were low and of the same order of magnitude as the in vivo rates of acetate activation to acetyl-CoA. The results show that ethanol is a poor substrate for Sch. pombe, even as an auxiliary energy source.