Monika Opałek, Agnieszka Marek, Aleksandra Kałdon, Barbara Mickowska, Dominika Wloch-Salamon

Increasing demand for food production requires improvements as well as openness to new sources of protein. Single Cell Protein derived from microbes has been intensively studied as a supplement for traditional sources of proteins, both for animal feed and direct human consumption. Food grade yeast, including Saccharomyces cerevisiae, has already been successfully used in industry. Here, we describe an artificial selection experiment that resulted in isolating Saccharomyces cerevisiae lines with a heritable phenotype characterized by significantly higher total protein content. Compared to the ancestral population, the average increase in protein content for all the evolved lines containing multiple-evolved clones was 5.4 g per 100g of dry mass (~15% of the total protein content). However, we also obtained specific clones with a total protein content increase of 9.3 g/100g dry mass (increase by 24.6%). Whole genome sequence analysis of mutations acquired by these clones allowed us to hypothesize about the role of the amino acid signaling pathway (SPS) disorders as a genetic base of the increased amino acid content. The proposed method is based on gradient fractionation of starved haploid yeast cells of different density, which reflects their physiological state regarding quiescence. We found a positive correlation in the fraction of non-quiescent cells in the starved populations and their amino acid content. Our method does not require any genetic modification. We believe that it can be successfully applied to other Saccharomyces sp. in order to increase the amino acid content stored in their cells. Beyond its implications for applied science, knowledge of the quiescent state in yeast is of fundamental importance to our understanding of the genetic basis of the G0 state in eukaryotic cells.