Evolving natural yeast to protein-rich micro-grain adaptable for non-sterile low-carbon biomanufacturing

A stable protein supply is essential for both human and planetary health. Low-carbon microbial manufacturing provides an arable land-independent and carbon-neutral route for protein supply, while it is limited by the natural capacity for cellular protein synthesis and high energy consumption for sterile fermentation. To address these challenges, a robust system was established for efficient protein synthesis from low-carbon acetic acid under non-sterile conditions. Yeast strains naturally capable of utilizing acetic acid under acid and high-salinity conditions were isolated from traditional fermented vegetables, and their unique ability to enable microbial protein production in non-sterile conditions, mineral medium containing acetic acid as the sole carbon source at pH = 5 or with additional 100 g/L NaCl, was validated. To further improve the protein yield, a high-throughput single cell screening method was developed to monitor the cellular macromolecule composition, and acid- and salt-tolerant strains were evolved for higher protein content, achieving an up to 7% improvement. Cultivation of the evolved strain under non-sterile conditions resulted in micro-grains with a protein content of 46 ± 2%. The robustness of the strain and process was further demonstrated through the valorization of low-cost industrial by-product acetic acid into protein. This work explores the potential of natural and artificial evolution and establishes a superior platform for protein-rich micro-grain synthesis through low-cost and low-carbon microbial manufacturing.