Production of yeastolates for uniform stable isotope labelling in eukaryotic cell culture

Preparation of stable isotope-labelled yeastolates opens up ways to establish more cost-effective stable isotope labelling of biomolecules in insect and mammalian cell lines and hence to employ higher eukaryotic cell lines for stable isotope labelling of complex recombinant proteins. Therefore, we evaluated several common yeast strains of the Saccharomycetoideae family as a source of high-quality, non-toxic yeastolates with the major aim to find a primary amino acid source for insect and mammalian cell culture that would allow cost-effective uniform stable isotope labelling (13C, 15N). Strains of the facultative methylotrophic yeasts Pichia pastoris and Hansenula polymorpha (Pichia angusta) as well as a strain of the baker's yeast Saccharomyces cerevisiae were compared as a source of yeastolate with respect to processing, recovery and ability to sustain growth of insect and mammalian cell lines. The best growth-supporting yeastolates were prepared via autolysis from yeast obtained from fed-batch cultures that were terminated at the end of the logarithmic growth phase. Yeastolates obtained from H. polymorpha performed well as a component of insect cell cultures, while yeastolates from S. cerevisiae and H. polymorpha both yielded good results in mammalian cell cultures. Growth of yeasts in Heine's medium without lactic acid allows relatively low concentrations of 13C and 15N sources, and this medium can be reused several times with supplementation of the 13C source only.