Abstract：
While thermotolerance is an attractive trait for yeasts used in industrial ethanol production, oxygen requirements of known thermotolerant species are incompatible with process requirements. Analysis of oxygen-sufficient and oxygen-limited chemostat cultures of the facultatively fermentative, thermotolerant species Ogataea parapolymorpha showed its minimum oxygen requirements to be an order of magnitude larger than those reported for the thermotolerant yeast Kluyveromyces marxianus. High oxygen requirements of O. parapolymorpha coincided with a near absence of glycerol, a key NADH/NAD+ redox-cofactor-balancing product in many other yeasts, in oxygen-limited cultures. Genome analysis indicated absence of orthologs of the Saccharomyces cerevisiae glycerol-3-phosphate-phosphatase genes GPP1 and GPP2. Co-feeding of acetoin, whose conversion to 2,3-butanediol enables reoxidation of cytosolic NADH, supported a 2.5-fold increase of the biomass concentration in oxygen-limited cultures. An O. parapolymorpha strain in which key genes involved in mitochondrial reoxidation of NADH were inactivated did produce glycerol, but transcriptome analysis did not reveal a clear candidate for a responsible phosphatase. Expression of S. cerevisiae GPD2, which encodes NAD+-dependent glycerol-3-phosphate dehydrogenase, and GPP1 supported increased glycerol production by oxygen-limited chemostat cultures of O. parapolymorpha. These results identify dependence on respiration for NADH reoxidation as a key contributor to unexpectedly high oxygen requirements of O. parapolymorpha.
摘要：
虽然耐热性是工业乙醇生产中使用的酵母的一个有吸引力的特性，已知耐热物质的氧需求与工艺要求不兼容。分析兼性发酵的氧充足和氧有限的恒化器培养物，耐热物种Ogataeaparaporpha显示其最低需氧量比耐热酵母Kluyveromycesmarxianus报告的最低需氧量大一个数量级。O.paraporpha的高需氧量与甘油的几乎不存在相吻合，许多其他酵母中的关键NADH/NAD+氧化还原辅因子平衡产品，在氧受限的培养物中。基因组分析表明酿酒酵母甘油-3-磷酸-磷酸酶基因GPP1和GPP2的直向同源物不存在。同时添加丙酮,其转化为2,3-丁二醇使胞质NADH的再氧化，在限氧培养物中，生物量浓度增加了2.5倍。参与NADH线粒体再氧化的关键基因被灭活的O.paraporpha菌株确实产生甘油，但转录组分析并没有揭示出一个明确的候选的负责任的磷酸酶。酿酒酵母GPD2的表达，其编码NAD依赖性甘油-3-磷酸脱氢酶，和GPP1支持通过O的氧限制恒化器培养物增加甘油产量。这些结果确定了对NADH再氧化的呼吸作用的依赖性，这是O.paraporpha意外高氧需求的关键因素。
