Inverse metabolic engineering for improving protein content in Saccharomyces cerevisiae

Production of Saccharomyces cerevisiae-based single cell protein (SCP) has recently received great attention due to the steady increase in the world's population and environmental issues. In this study, an inverse metabolic engineering approach was applied to improve the production of yeast SCP. Specifically, an S. cerevisiae mutant library, generated using UV-random mutagenesis, was screened for three rounds to isolate mutants with improved protein content and/or concentration. The #1021 mutant strain exhibited a respective 31% and 23% higher amino acid content and concentration than the parental S. cerevisiae D452-2 strain. Notably, the content, concentration, and composition of amino acids produced by the PAN2* strain, with a single nucleotide polymorphism in PAN2 coding for a catalytic subunit of the poly(A)-nuclease (PAN) deadenylation complex, were virtually identical to those produced by the #1021 mutant strain. In a glucose-limited fed-batch fermentation, the PAN2* strain produced 19.5 g L^-1 amino acids in 89 h, which was 16% higher than that produced by the parental D452-2 strain. This study highlights the benefits of inverse metabolic engineering for enhancing the production titer and yield of target molecules without prior knowledge of rate-limiting steps involved in their biosynthetic pathways.