methanocaldococcus methanocaldococcus methanocaldococcus formerly known as methanococcus is a genus of coccoid methanogen archaea. they are all mesophiles, except the thermophilic m. thermolithotrophicus and the hyperthermophilic m. jannaschii. the latter was discovered at the base of a “white smoker” chimney at 21°n on the east pacific rise and it was the first archaean genome to be completely sequenced, revealing many novel and eukaryote-like elements. methanocaldococcus scientific classification domain: archaea kingdom: euryarchaeota phylum: euryarchaeota class: methanococci order: methanococcales family: methanocaldococcaceae genus: methanocaldococcuswhitman 2002 type species methanocaldococcus jannaschii(jones et al. 1984) whitman 2002 species m. bathoardescens m. fervens m. indicus m. infernus m. jannaschii m. villosus m. vulcanius nomenclature the name methanocaldococcus has latin and greek roots, methano for methane, caldo for hot, and the greek kokkos for the spherical shape of the cells. overall, the name means spherical cell that produces methane at hot temperatures. metabolism all species in methanocaldococcus are obligate methanogens. they use hydrogen to reduce carbon dioxide. unlike many other species within euryarchaeota, they cannot use formate, acetate, methanol or methylamines as substrates. phylogeny the currently accepted taxonomy is based on the list of prokaryotic names with standing in nomenclature (lpsn) and national center for biotechnology information (ncbi). 16s rrna-based ltp_01_2022 53 marker proteins based gtdb 07-rs207 methanocaldococcaceae m. villosus bellack et al. 2011 m. indicus l'haridon et al. 2003 m. infernus (jeanthon et al. 1998) whitman 2002 m. vulcanius (jeanthon et al. 1999) whitman 2002 m. jannaschii (jones et al. 1984) whitman 2002 (type sp.) m. bathoardescens stewart et al. 2015 m. fervens (jeanthon et al. 1999) whitman 2002 methanocaldococcus methanocaldococcaceae m. villosus m. infernus m. fervens m. bathoardescens m. jannaschii m. vulcanius methanocaldococcus