Nitrogen limitation leads to evolution of pseudo-invasive growth in Saccharomyces cerevisiae but not elimination of the Crabtree effect.
Renata Usaite (1), Jens Nielsen (1), Birgitte Regenberg (2)
(1) Center for Microbial Biotechnology, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark; (2) Biozentrum, Universität Frankfurt am Main, Marie-Curie-Str., Frankfurt am Main, 60439, Germany
Many fungi change from a yeast form to a pseudo invasive form when exposed to nitrogen limitation. To understand the long-term effects of nitrogen limitations, we grew a non-invasive form of S. cerevisiae, CEN.PK-113-7D, under glutamine and ammonium limiting conditions for several hundred generations. Transcript analysis from cells grown under glutamine limiting conditions showed that transcripts involved in cell wall biosynthesis and filamentation are up regulated compared to the parental strain. This phenotype is also reflected at the morphological level, as the evolved cells were elongated with irregular budding and invasive growth. However, cells grown under ammonium limiting conditions did not change transcript profiles or morphology significantly, not even after more than 400 generations in several cultures. This lack of drift may reflect that this yeast has already adapted to conditions where ammonium is the main nitrogen source. Yeast exposed to nitrogen limitation also produces ethanol in expense of biomass. We expected that cells would overcome this effect when evolving under the nitrogen limiting conditions. Though the selective pressure for a better carbon utilisation was big, CEN.PK did not reduce the ethanol production in any of the cultures.