Enhanced amino acid biosynthesis in Phaffia rhodozyma via herbicide-induced selection

According to the Food and Agricultural Organisation 2024 statement, developing single-cell protein technology is important to reduce the burden on conventional feed protein production sectors. In this regard, improved commercial strains rich in amino acids, especially Lys and Met, may provide a sustainable alternative source of protein in aquaculture diets. The developed and laboratory-validated methodology for creating protein-synthesizing mutants will strengthen the competitiveness of SCP production technology. The present work provides unique results on improving the protein-producing properties of wild-type Phaffia rhodozyma DSM 5626 by mutagenesis and screening on herbicide-containing medium as a selective agent for amino acid biosynthesis inhibition. Inhibitory concentrations of pure herbicide actives were determined for S-(2-aminoethyl)-L-cysteine (AEC) hydrochloride and glufosinate-ammonium (GA) for complete inhibition and strong inhibition of the DSM 5626 strain. GA at a concentration of 50 mM and 100 mM and AEC at 0.5 mM and 2.5 mM were chosen for mutant selection after chemical mutagenesis. The use of herbicides resulted in the selection of mutants with significantly improved synthesis of Met and Lys. Specifically, mutants GA6/4 and GA7/5 exhibited 37% and 26% higher Met levels, respectively, while GA6/3 had a 14% increase in Lys compared to the wild-type strain. The AEC3/9 mutant demonstrated a 35% increase in Met, 24% in Lys, 8% in Ile, and 6% in Phe, underscoring the efficacy of this screening approach in enhancing essential amino acid content. The protein quality parameters essential amino acid index and amino acid score of these mutants became higher compared with commercial strains of SCP yeast such as C. utilis, S. cerevisiae, K. marxianus, etc.

Mutagenesis combined with selective screening using herbicides is an effective approach to enhancing amino acid biosynthesis in yeast.