Methanotorris formicicus sp. nov., a novel extremely thermophilic, methane-producing archaeon isolated from a black smoker chimney in the Central Indian Ridge

Researchers isolated a novel extremely thermophilic, methane-producing archaeon from a black smoker chimney at the Kairei hydrothermal field in the Central Indian Ridge at 2,421 meters depth. The isolate, designated strain Mc-S-70T, consists of irregular cocci with multiple flagella but is non-motile in culture. It grows between 55-83°C with optimal growth at 75°C and between pH 6.0-8.5 with optimal pH 6.7. The organism is a strictly anaerobic, autotrophic methanogen that uses hydrogen and carbon dioxide as sole energy and carbon sources, with formate serving as an alternative energy source. Phylogenetic analysis based on 16S rRNA gene sequences shows the isolate is most closely related to Methanotorris igneus but is genetically distinct by DNA-DNA hybridization analysis. Multiple physiological differences distinguish it from M. igneus, including lower optimal growth temperature, neutral pH optimum, and ability to utilize formate. The genomic DNA has 33.3 mol% G+C content. Based on genetic and physiological characterization, the researchers propose this as a novel species, Methanotorris formicicus sp. nov., with type strain Mc-S-70T.

Key findings

• Methanotorris formicicus is the first extremely thermophilic methanogen in the order Methanococcales with optimal growth at 75°C, approximately 10°C lower than the related species M. igneus
• The isolate is an autotrophic methanogen that uniquely uses formate as an alternative energy source in addition to hydrogen and carbon dioxide
• Phylogenetic analysis shows 97.8% 16S rRNA gene similarity to M. igneus, but DNA-DNA hybridization at only 5.1% relatedness confirms it as a genetically distinct species
• The organism exhibits intermediate physiological traits between hyperthermophilic and thermophilic methanogens, suggesting evolutionary intermediates within the Methanococcales order