What is "methanocaldococcus"

In taxonomy, Methanocaldococcus is a genus of the Methanocaldococcaceae.

Methanocaldococcus formerly known as Methanococcus is a genus of coccoid methanogens. 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.