Effect of MIG1 Gene Deletion on Lactose Utilization in Lac⁺ Saccharomyces cerevisiae Engineering Strains

Abstract

A lactose-consuming Saccharomyces cerevisiae strain EY-510 was constructed by expressing LAC4 and LAC12 gene of Kluyveromyces marxianus in the host strain AY-5. Mig1 is a zinc finger DNA-binding protein that plays a critical role on glucose repression in S. cerevisiae. In order to study in anaerobic condition the degree of glucose repressing galactose metabolism, a deletion fragment MIGIA-KanMX-MIG1B was transformed into AY-5, resulting a Δmig1 strain DY-510. In order to study whether the presence of glucose inhibits the consumption of lactose, a Lac⁺ Δmig1 strain RY-510 was constructed by transforming the deletion fragment into EY-510. Galactose consumption was initiated at higher glucose concentrations in the MIG1 deletion strain RY-510 and DY-510 than in the corresponding wild-type strain AY-5 and EY-510, wherein galactose was consumed until glucose was completely depleted in the mixture. On lactose medium, the duration of fermentation for RY-510 was 168 h, whereas the duration for EY-510 was 252 h. The lactose uptake rate was 0.357 g/L/h for RY-510 and that was 0.238 g/L/h for EY-510. The ethanol productivity of RY-510 was 0.127 g/L/h and that was 0.085 g/L/h for EY-510. And in cheese whey powder solution medium, RY-510 was able to produce 30.25 g/L ethanol from 76.8 g/L initial lactose in 190 h, during which EY-510 was able to consume 70.8 % of the initial lactose and produced 24.14 g/L ethanol. Therefore, relieving glucose control provides an approach for constructing lactose-consuming S. cerevisiae.