Evolutionary engineering of yeast for closed-circulating ethanol fermentation in PDMS membrane bioreactor

Based on evolutionary engineering, a regimen of step transfer cultivation was designed to breed a yeast strain that adapted the process of closed-circulating ethanol fermentation in PDMS membrane bioreactor. The kinetic parameters of the fermentation such as ethanol concentration in the broth, cell concentration and death ratio, ethanol productivity and specific ethanol production rate behaved the same tendency in varied tests. During the fermentation with the screened strain S232, the glucose utilization, ethanol productivity, ethanol yield on glucose, ethanol yield on biomass and specific ethanol production rate were 3.81 g/L/h, 1.63 g/L/h, 0.427 g/g, 194.3 g/g and 0.385 g/g/h, and had elevation of 7.32%, 10.13%, 2.64%, 14.97% and 19.57% over those of fermentation with the parent strain S3, respectively. These results indicated the screened yeast strain had mutated during the fermentation. The yeast strains bred by the regimen not only adapted to the closed-circulating fermentation process but also could be used for general fermentation process.

► A regimen of step transfer cultivation was designed based on the evolutionary engineering. ► The superior yeast strains were obtained in the closed-circulating system. ► The screened strains had an increased fermentation performance compared to the parent strain. ► The fermentation kinetic parameters behaved the same tendency in varied tests. ► It was an effective method to breed yeast strain by the step transfer regimen.