methanobrevibacter oralis methanobrevibacter oralis methanobrevibacter oralis is a species of coccobacillary, non-motile, gram-positive, methane-producing archaeon. methanobrevibacter oralis scientific classification domain: archaea kingdom: euryarchaeota phylum: euryarchaeota class: methanobacteria order: methanobacteriales family: methanobacteriaceae genus: methanobrevibacter species: m. oralisferrari et al. 1995