Optimization of an ethanol production medium in very high gravity fermentation.

Concentrations of Mg(2+), glycine, yeast extract, biotin, acetaldehyde and peptone were optimized by a uniform design process for ethanol production by Saccharomyces cerevisiae. Using non-linear step-wise regression analysis, a predictive mathematical model was established. Concentrations of Mg(2+) and peptone were identified as the critical factors: 50 mM Mg(2+) and 1.5% (w/v) peptone in the medium increased the final ethanol titre from 14.2% (v/v) to 17% (v/v) in 48 h.

[Progress on engineered strains for ethanol production].

With the 21 century's coming, the era of cheap oil is coming to the end. There has been an increasing worldwide interest in fuel ethanol. In the last two decades, lots of work has been done to develop strains for ethanol producing. Research progress on metabolic engineering of strains for fuel ethanol production is summarized, including genetically engineered Saccharomyces cerevisiae to utilize starch, pentose and cellulose, Zymomonas mobilis to ferment arabinose and xylose, Escherichia coli and Klebsiella oxytoca to introduce heterogenous ethanol production pathway. The aim of engineering these strains is to obtain an ideal microorganism which can converse the available carbon sources to ethanol rapidly and efficiently with high tolerance to ethanol and to inhibitory components in the cheap materials such as lignocellulose hydrolysate. The importance of fuel ethanol will be a stimulus to develop engineered hardy strains to utilize cheap materials for high ethanol concentration production. Since both Saccharomyces cerevisiae and Zymomonas mobilis are generally regarded as safe (GRAS), genetically engineered Saccharomyces cerevisiae which can utilize raw starch directly and recombinant Zymomonas mobilis which can ferment glucose, arabinose and xylose in the lignocellulose hydrolysate have potential application to industry in the near future.