Cellular responses of Saccharomyces cerevisiae towards ethanol- or heat-induced stresses

Abstract

Saccharomyces cerevisiae는 ethanol 생산 균주로서 다양한 용도로 이용 되어왔으나 고농도의 ethanol과 heat에는 취약하여 성장과 발효가 억제된다. 본 연구에서는 S. cerevisiae의 physiology에 ethanol과 heat이 미치는 영향에 대해 연구하였다. YNB 배지에 ethanol을 0%에서 8%까지 첨가하였을 때 성장속도가 이에 비례하여 감소하였고 배양온도를 38 ℃에서 42 ℃ 로 증가시켰을 때에도 마찬가지로 이에 비례하여 감소하였다. Ethanol 농도가 증가할 수록 specific glucose uptake rate와 specific ethanol production rate는 감소하였는데 반면 고온에서는 모두 증가하였다. Exponential growth phase 구간에서 carbon flux analysis를 실시하였는데 이를 통해 S. cerevisiae가 고농도의 ethanol과 고온의 조건에서는 많은 양의 cellular maintenance energy를 필요로 하다는 것을 알 수 있었다. Ethanol stress하에서는 TCA cycle flux를 증가시키고 heat stress 하에서는 TCA cycle flux와 ethanol production pathway를 동시에 증가시켜 maintenance energy를 보충하는 것으로 사료되었다. 세포 내 ROS 함량 분석을 통해 stress 상황에서 ROS가 증가하여 cell에 손상을 입히고 이를 극복하기 위해 maintenance energy를 다량 필요로 하는 것으로 사료되었다.;Saccharomyces cerevisiae is an excellent ethanol producer, but is rather sensitive to high concentration of ethanol and high temperature. Here, influences of ethanol and heat on physiology of S. cerevisiae were investigated. The specific growth rate was almost linearly reduced with ethanol concentration from zero to 8% (v/v) and also with temperature from 38 to 42oC during growth in YNB medium. Interestingly, the specific glucose uptake rate and the specific ethanol production rate both were linearly decreased with ethanol concentration. However, the high temperature resulted in the increased specific glucose uptake rate and the specific ethanol production rate. The carbon flux analysis and ATP balance during the fermentation indicated that S. cerevisiae required larger amount of cellular maintenance energy in the presence of high concentration of ethanol and under high temperature. The maintenance energy was generated mainly via increased carbon flux into TCA cycle with ethanol stress, whereas increase of carbon flux into TCA cycle and into ethanol fermentation pathway both was used with heat stress. The analysis of reactive oxygen species (ROS) inside cells suggested that one of the factors to increase cellular maintenance energy could be generation of ROS under the stressful conditions.