Influence of furfural on anaerobic glycolytic kinetics of Saccharomyces cerevisiae in batch culture

Furfural was reduced to furfuryl alcohol by Saccaromyces cerevisiae with a yield of 0.97 +/- 0.01 mmol/mmol causing a lag phase in cell growth. in the presence of 29 mM, furfural the cell-mass yield on glucose decreased from 11.0 +/- 0.1 mg/mmol (0.06 +/- 0.0006 g/g) in a reference fermentation with out furfural to 9.7 +/- 0.07 mg/mmol (0.05 +/- 0.0004 g/g), whereas the eth anol yield on glucose increased from 1.6 +/- 0.03 to 1.7 +/- 0.03 mmol/mmol . No glycerol was excreted during furfural reduction, and the lag phase in acetate production was extended from 1 h in the reference fermentation to 5 h in the presence of furfural. Acetaldehyde and pyruvate were excreted dur ing the furfural reduction phase. Cell growth and cell maintenance were pro portional to glucose consumption during the entire fermentation, whereas th e cell-mass yield on ATP produced was low during furfural reduction. These observations indicate that furfural addition to a batch culture decreased c ell replication without inhibiting cell activity (designated as replicative inactivation). The absence of glycerol production during furfural reductio n suggests that furfural acted as an alternative redox sink oxidizing exces s NADH formed in biosynthesis. A mechanistic mathematical model was develop ed that described accurately the fermentation in the absence and presence o f furfural. The model was based on the assumptions that: (i) furfural reduc tion to furfuryl alcohol by NADH-dependent dehydrogenases had a higher prio rity than reduction of dihydroxyacetone phosphate to glycerol; and (ii) fur fural caused inactivation of cell replication. The effect of furfural on ce ll replication is discussed in relation to acetaldehyde formation. Inactiva tion of cell replication was modeled by considering two populations within the cell culture, both metabolically active, but only one replicating. The kinetic description was developed as a tool to estimate transient fluxes of carbon, NADH/NAD(+) and ATP/ADP. (C) 1999 John Wiley & Sons, Inc.