Methylomonas methanica and Methylosinus sp. co-cultivated with methylotrophs under saline conditions for microbial protein production from biogas as alternatives to natural-gas- based production using Methylococcus capsulatus

Abstract

Microbial protein (MP) is a promising alternative protein source that can be produced using methane as a substrate derived from undervalued resources. Methylococcus capsulatus is one of the most prominent microbial species employed for industrial production, while other potentially suitable methanotrophs remain underexplored. Here, we selected the alternative methanotrophs Methylosinus sp. and Methylomonas methanica with high growth rates and potential for halotolerance and compared them to M. capsulatus . Methylosinus sp. and Methylomonas methanica achieved up to 1.87-fold higher maximum specific growth rates and 2.52-fold higher biomass concentrations, compared to M. capsulatus . When the pH was allowed to acidify below optimum for growth, the protein content of M. methanica (45% ± 5% CDW) was 1.55 times compared to pH-controlled conditions. Cultivation at an increased salt content (20 g NaCl L −1 ) boosted the protein content of M. methanica to 81% ± 7% CDW, showing its applicability for MP production using saline water. Co-culturing M. methanica with the methylotrophic yeast Komagataella phaffii led to a 1.27-fold higher essential amino acid content, which indicates an improvement in protein quality, while the use of synthetic biogas increased the protein yields up to 1.5-fold, compared to purified methane. In summary, M. methanica co-cultured with selected methylotrophs has the potential to enable more sustainable MP production under saline conditions using biogas, as an alternative to natural gas-based production with M. capsulatus . These strategic upstream choices could bring us closer to a future-proof protein production system.