(191dr) Anaerobiosis revisited: yeast physiology under extremely low oxygen availability

The budding yeast Saccharomyces cerevisiae plays an important role in biotechnological applications, ranging from fuel ethanol to recombinant protein production. It is also used as a model organism to understand eukaryotic gene regulation and cellular physiology. S. cerevisiae’s ability to grow under anaerobic conditions is of particular interest for some industrial applications, in order to maximize product formation and decrease costs related to mixing and aeration. Despite the abundant amount of information and the industrial relevance, it is still not conclusive whether S. cerevisiae can grow under complete anaerobiosis, since the biosynthesis of lipids requires molecular O₂. Thus, we revisited the much-studied fermentative metabolism in S. cerevisiae using a set of well-defined experiments to clarify if it can indeed grow under complete anaerobiosis. We used an O₂ trap (OTC-2, Agilent) coupled to a N₂ stream (Certified; 5.2, Air Products, < 3 ppm O₂), to provide an inlet N₂ gas with less than 15 ppb O₂. Under such severe O₂ limitation in a chemostat cultivation without lipid supplementation, the biomass concentration dropped, but washout did not occur_.By performing lipidomics, we noticed that the fraction of unsaturated fatty acids in cells dropped to 40.5% (w/w), as compared to 70% when cultivated with oleic acid/ergosterol. The same cultivation system was used to grow other yeast species (Kluyveromyces lactis and K. marxianus) and the results attained will be compared to those involving S. cerevisiae.