Sárvári Horváth Ilona, Franzén Carl Johan, Taherzadeh Mohammad J, Niklasson Claes, Lidén Gunnar
Department of Chemical Reaction Engineering, Chalmers University of Technology, S-412 96 Göteborg, Sweden.
Appl Environ Microbiol. 2003 Jul;69(7):4076-86. doi: 10.1128/AEM.69.7.4076-4086.2003.
Effects of furfural on the aerobic metabolism of the yeast Saccharomyces cerevisiae were studied by performing chemostat experiments, and the kinetics of furfural conversion was analyzed by performing dynamic experiments. Furfural, an important inhibitor present in lignocellulosic hydrolysates, was shown to have an inhibitory effect on yeast cells growing respiratively which was much greater than the inhibitory effect previously observed for anaerobically growing yeast cells. The residual furfural concentration in the bioreactor was close to zero at all steady states obtained, and it was found that furfural was exclusively converted to furoic acid during respiratory growth. A metabolic flux analysis showed that furfural affected fluxes involved in energy metabolism. There was a 50% increase in the specific respiratory activity at the highest steady-state furfural conversion rate. Higher furfural conversion rates, obtained during pulse additions of furfural, resulted in respirofermentative metabolism, a decrease in the biomass yield, and formation of furfuryl alcohol in addition to furoic acid. Under anaerobic conditions, reduction of furfural partially replaced glycerol formation as a way to regenerate NAD+. At concentrations above the inlet concentration of furfural, which resulted in complete replacement of glycerol formation by furfuryl alcohol production, washout occurred. Similarly, when the maximum rate of oxidative conversion of furfural to furoic acid was exceeded aerobically, washout occurred. Thus, during both aerobic growth and anaerobic growth, the ability to tolerate furfural appears to be directly coupled to the ability to convert furfural to less inhibitory compounds.
通过进行恒化器实验研究了糠醛对酿酒酵母有氧代谢的影响，并通过进行动态实验分析了糠醛转化的动力学。糠醛是木质纤维素水解产物中存在的一种重要抑制剂，已证明其对呼吸生长的酵母细胞具有抑制作用，且这种抑制作用远大于先前观察到的对厌氧生长酵母细胞的抑制作用。在所有获得的稳态下，生物反应器中的残留糠醛浓度均接近零，并且发现在呼吸生长过程中糠醛仅转化为糠酸。代谢通量分析表明，糠醛影响能量代谢相关的通量。在最高稳态糠醛转化率下，比呼吸活性增加了50%。在脉冲添加糠醛期间获得的更高糠醛转化率导致呼吸发酵代谢、生物质产量下降，除了糠酸之外还形成了糠醇。在厌氧条件下，糠醛的还原部分替代了甘油的形成，作为再生NAD+的一种方式。当糠醛浓度高于入口浓度时，糠醇的产生完全替代了甘油的形成，导致细胞被冲出。同样，当有氧条件下糠醛氧化转化为糠酸的最大速率被超过时，也会发生细胞被冲出。因此，在有氧生长和厌氧生长过程中，耐受糠醛的能力似乎直接与将糠醛转化为抑制性较小的化合物的能力相关联。
