A study on bioethanol production by galactose-utilizing saccharomyces cerevisiae KL17

Abstract

A wild-type yeast strain of Saccharomyces cerevisiae KL17 was screened from the soil. The cell growth and ethanol production of S.cerevisiae KL17 at different concentrations of glucose and/or galactose in the range of 2 ~ 10% were tested and compared with those of an industrial S.cerevisiae. The performance of both strains was evaluated at a high-ethanol level condition also, simulating the industrial practice for etha-nol production. The fed-batch mode was employed to achieve high ethanol concentrations up to about 95 g/L. In overall, S.cerevisaie KL17 showed a slightly better ethanol productivity with a slightly less cell growth than the control, which implied that it was a good candidate as industrial yeast strain for ethanol production from glucose and/or galactose. When S.cerevisiae KL17 was pre-cultured in a YPD medium containing glucose as the main carbon source and inoculated into a YPG medium containing galactose, a significant time lag was observed in the beginning of the batch culture using galactose. By using YPG in-stead of YPD for pre-culture, the time lag and thus galactose depletion time could be shortened. The maxi-mum concentration of ethanol produced with a YPG pre-culture was 4.5% and 6.6% higher than those with a pre-culture when 2.5% glucose + 2.5% galactose, and 5% galactose, respectively were used for the main culture. The time points when the ethanol concentration reached a maximum value were about 3 hours earlier with a YPG pre-cultured. Fed-batch cultures were also performed. A maximum ethanol concentration of 96.9 g/L was achieved observed at 28 h. Such a high ethanol productivity of S.cerevisiae KL17 clearly proved its good potential as an industrial strain. Enhancement of the ethanol stress tolerance of S.cerevisiae KL17 by introducing salC or salCE gene originated from Streptomyce albus was tested under ethanol stress of 0 % and 10 %. The three transformants showed a better growth under 10 % of ethanol stress condition. Especiall...