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

Authors: 
Karoly Gombert, A., University of Campinas
da Costa, B. L. V., University of Campinas
Raghavendran, V., Chalmers University of Technology
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.