Effects of Oxygen Limitation on Xylose Fermentation,Intracellular Metabolites, and Key Enzymes of Neurospora crassa AS3.1602

摘要

The effects of oxygen limitation on xylose fermentation of Neurospora crassa AS3.1602 were studied using batch cultures. The maximum yield of ethanol was 0.34 g/g atoxygen transfer rate (OTR) of 8.4 mmol/Lh. The maximum yield of xylitol was 0.33 g/g atOTR of 5.1 mmol/Lh. Oxygen limitation greatly affected mycelia growth and xylitol andethanol productions. The specific growth rate (μ) decreased 82% from 0.045 to 0.008 h~(-1)when OTR changed from 12.6 to 8.4 mmol/Lh. Intracellular metabolites of the pentosephosphate pathway, glycolysis, and tricarboxylic acid cycle were determined at variousOTRs. Concentrations of most intracellular metabolites decreased with the increase inoxygen limitation. Intracellular enzyme activities of xylose reductase, xylitoldehydrogenase, and xylulokinase, the first three enzymes in xylose metabolic pathway,decreased with the increase in oxygen limitation, resulting in the decreased xylose uptakerate. Under all tested conditions, transaldolase and transketolase activities alwaysmaintained at low levels, indicating a great control on xylose metabolism. The enzyme ofglucose-6-phosphate dehydrogenase played a major role in NADPH regeneration, and itsactivity decreased remarkably with the increase in oxygen limitation.