Characterization of the Nitrogen-fixing, Hyperthermophilic Methanogen Methanocaldococcus strain FS406-22

SMSU Event Center BC

Methanocaldococcus FS406-22 is a methanogenic archaeon that was previously isolated from a deep-sea hydrothermal vent. It was experimentally determined to perform nitrogen fixation at 92°C, 28°C higher than the previously known upper temperature limit of biological nitrogen fixation. The initial study reporting strain FS406-22 characterized its growth rates at different temperatures under nitrogen fixing conditions, but a thorough characterization has yet to be determined. This study aims to further characterize FS406-22 using phenotypic tests and comparative genomic analysis, so that it can be formally described as a new taxon. Growth characterization of FS406-22 included determining pH range, utilization of potential electron donors other than molecular hydrogen, and specific growth rates at different temperatures. These tests performed under ammonia grown conditions further physiologically distinguish FS406-22 from other Methanocaldococcus species. Growth under ammonia grown conditions was observed between 60°C and 92°C with optimal growth at 85°C and 87.5°C (doubling time 40 minutes), and growth under nitrogen fixing conditions was not observed above 90°C FS406-22 grew between a pH of 4.5 and 6.5. Formate is utilized as an alternate carbon substrate. The genome sequence of FS406-22 consists of a 1.76 Mb circular chromosome and a 12.2 kb plasmid. The genome of FS406-22 shares between 28.3-33.5% in silico DNA-DNA cross-hybridization (DDH) to all other described species in the genus Methanocaldococcus, indicating that FS406-22 represents a distinct species (