Methanotrophs mediated biogas valorization: Sustainable route to polyhydroxybutyrate production.

This study explores the ability of methanotrophs to convert biogas into biopolymers, addressing H2S as a limitation in the utilization of biogas as a carbon source for bioconversion. Transcriptomic analysis was conducted to understand the growth and changes in the expression patterns of Type I and II methanotrophs under varying H2S concentrations. Results suggested that Type II methanotrophs can possess a native H2S utilization pathway. Both Type I and II methanotrophs were evaluated for their growth and polyhydroxybutyrate (PHB) production from biogas. Methylocystis sp. MJC1 and Methylocystis sp. OK1 exhibited a maximum biomass production of 4.0 and 4.5 gDCW/L, respectively, in fed-batch culture, aligning with the transcriptome data. Furthermore, Methylocystis sp. MJC1 produced 2.9 g PHB/L from biogas through gas fermentation. These findings underscore biogas-based biotechnology as an innovative solution for environmental and industrial challenges with further optimization and productivity enhancement research expected to broaden the potential in this field.

Comparative genomic analysis of Methylocystis sp. MJC1 as a platform strain for polyhydroxybutyrate biosynthesis.

Biodegradable polyhydroxybutyrate (PHB) can be produced from methane by some type II methanotroph such as the genus Methylocystis. This study presents the comparative genomic analysis of a newly isolated methanotroph, Methylocystis sp. MJC1 as a biodegradable PHB-producing platform strain. Methylocystis sp. MJC1 accumulates up to 44.5% of PHB based on dry cell weight under nitrogen-limiting conditions. To facilitate its development as a PHB-producing platform strain, the complete genome sequence of Methylocystis sp. MJC1 was assembled, functionally annotated, and compared with genomes of other Methylocystis species. Phylogenetic analysis has shown that Methylocystis parvus to be the closest species to Methylocystis sp. MJC1. Genome functional annotation revealed that Methylocystis sp. MJC1 contains all major type II methanotroph biochemical pathways such as the serine cycle, EMC pathway, and Krebs cycle. Interestingly, Methylocystis sp. MJC1 has both particulate and soluble methane monooxygenases, which are not commonly found among Methylocystis species. In addition, this species also possesses most of the RuMP pathway reactions, a characteristic of type I methanotrophs, and all PHB biosynthetic genes. These comparative analysis would open the possibility of future practical applications such as the development of organism-specific genome-scale models and application of metabolic engineering strategies to Methylocystis sp. MJC1.