Methylococcaceae

Methylococcaceae is a family of Gram-negative, aerobic methanotrophic bacteria within the order Methylococcales of the class Gammaproteobacteria. Members use methane as their sole carbon and energy source, oxidizing it with methane monooxygenase and directing carbon into central metabolism. The family includes several genera, notably Methylococcus, Methylomonas, Methylomicrobium, and Methylocaldum.

Physiology and metabolism: All known Methylococcaceae possess methane monooxygenase, enabling the oxidation of methane to methanol. Some strains also carry soluble methane monooxygenase as an alternative enzyme. Carbon is mainly assimilated via the ribulose monophosphate (RuMP) pathway, characteristic of Type I methanotrophs within Gammaproteobacteria, while energy is conserved through oxidation steps ending in CO2. Cells often contain internal membrane systems associated with methane oxidation.

Ecology and significance: Members are widespread in soil, freshwater, marine environments, wetlands, rice paddies, and landfills, where they consume methane and contribute to mitigating methane emissions. They can occur as free-living organisms in sediments or water columns and, in some habitats, form associations with plants. Some species are explored for biotechnology, including conversion of methane to biomass or products such as polyhydroxyalkanoates.

Taxonomy and genomics: Methylococcaceae is a taxonomic group within Gammaproteobacteria and has undergone revisions as new genomic data become available. Genomic analyses commonly identify pmoCAB genes encoding the particulate methane monooxygenase, with some genomes also containing genes for soluble methane monooxygenase. Ongoing sequencing and characterization continue to refine the classification and ecological roles of the family’s genera.