From C1 compounds to microbial protein as a food source

Microbial protein (MP) – the biomass of bacteria, yeasts, filamentous fungi and microalgae – is an alternative protein source that could play a key role in the fight against climate change. One-carbon (C1) substrates are attractive for MP production due to their efficient production from CO2 and renewable electricity, linking carbon capture to food production, making use of resources in an efficient manner and circumventing agriculture. Here we compared all reported combinations of C1 (formate/methanol/methane) and microorganisms (bacteria/yeasts), considering process and engineering parameters as well as biomass quality, with special attention paid to the amino acid match with human requirements. This meta-analysis based on >100 studies suggests that methanol is the most promising C1 substrate for MP production due to its efficient production from CO2, the high biomass yields and production rates, as well as the low reactor cooling needs. Furthermore, methanol-grown microorganisms seem best suited for human nutrition due to their high protein content and balanced amino acid profile. Due to the high nutritional quality of MP, 3.3 times less MP from C1 compared to egg mass (218 g) and 1.9 times less MP mass compared to soybean (130 g) are required to cover the daily needs of an average adult. Finally, our analysis shows that cysteine is the limiting amino acid for 65-73% of methane- and methanol-grown bacteria, while methionine is limiting in 55% of the cases of methanol-grown yeasts, which could be tuned by deploying metabolic engineering tools yielding microorganisms with steered amino acid profiles