Abstract
Bioethanol is the largest biotechnology product and the most dominant biofuel globally. Saccharomyces cerevisiae is the most favored microorganism employed for its industrial production. However, obtaining maximum yields from an ethanol fermentation remains a technical challenge, since cellular stresses detrimentally impact on the efficiency of yeast cell growth and metabolism. Ethanol fermentation stresses potentially include osmotic, chaotropic, oxidative, and heat stress, as well as shifts in pH. Well-developed stress responses and tolerance mechanisms make S. cerevisiae industrious, with bioprocessing techniques also being deployed at industrial scale for the optimization of fermentation parameters and the effective management of inhibition issues. Overlap exists between yeast responses to different forms of stress. This review outlines yeast fermentation stresses and known mechanisms conferring stress tolerance, with their further elucidation and improvement possessing the potential to improve fermentation efficiency.
Highlights
The biotechnological potential of Saccharomyces cerevisiae has been exploited traditionally for the purposes of baking, brewing, and wine making
High initial fermentable sugar concentrations is pertinent to first-generation bioethanol production, with high initial external osmolarity in an alcoholic fermentation facilitating the passive diffusion of cellular water down the concentration gradient, leading to hyperosmotic stress [106]
Stress due to high temperatures can be encountered in ethanol fermentations, in the early stages or if the external temperature is higher than the optimum for the fermentation [149,150]
Summary
The biotechnological potential of Saccharomyces cerevisiae has been exploited traditionally for the purposes of baking, brewing, and wine making. Its fermentative nature evolved between 125 and 150 million years ago and is shared by many yeast species, but the acquisition of ethanol tolerance by S. cerevisiae is a more recent event occurring after the whole genome duplication event, which is believed to have happened 100 million years ago [3,4]. This ~6000 gene-containing unicellular eukaryote was the first organism to have its genome fully sequenced [5,6].
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