biosynthesis of vitamin c by yeast leads to increased stress resistance由酵母生物合成的维生素c会导致压力增加阻力.pdf

Biosynthesis of Vitamin C by Yeast Leads to Increased Stress Resistance 1 1 2,3 1 2,3 1 Paola Branduardi , Tiziana Fossati , Michael Sauer , Roberto Pagani , Diethard Mattanovich , Danilo Porro * ` 1 Dipartimento di Biotecnologie e Bioscienze, Universita degli Studi di Milano-Bicocca, Milano, Italy, 2 School of Bioengineering, University of Applied Sciences, Vienna, Austria, 3 Institute of Applied Microbiology, University of Natural Resources and Applied Life Sciences, Vienna, Austria Background. In industrial large scale bio-reactions micro-organisms are generally exposed to a variety of environmental stresses, which might be detrimental for growth and productivity. Reactive oxygen species (ROS) play a key role among the common stress factors–directly-through incomplete reduction of O2 during respiration, or indirectly-caused by other stressing factors. Vitamin C or L-ascorbic acid acts as a scavenger of ROS, thereby potentially protecting cells from harmful oxidative products. While most eukaryotes synthesize ascorbic acid, yeast cells produce erythro-ascorbic acid instead. The actual importance of this antioxidant substance for the yeast is still a subject of scientific debate. Methodology/Principal Findings. We set out to enable Saccharomyces cerevisiae cells to produce ascorbic acid intracellularly to protect the cells from detrimental effects of environmental stresses. We report for the first time the biosynthesis of L-ascorbic acid from D-glucose by metabolically engineered yeast cells. The amount of L-ascorbic acid produced leads to an improved robustness of the recombinant cells when they a