New Archaea Species Found in Japanese Gas Field

Biofilm samples were collected from a gas production well, KTG3, in the Southern Kanto gas field (Chiba Prefecture, Japan). The samples were taken after brine eruptions on 29 August 2019, 16 July 2020, and 11 May 2023.

The gas field is located in an old marine forearc basin, with subsurface gas reservoirs in turbidite sandstones. The brine from KTG3 is rich in organic matter, iodine, and iron.

The collected biofilm was placed in a 100 ml glass bottle filled with brine and transported to the laboratory under refrigerated conditions. It was also inoculated in 50 ml glass vials with anaerobic medium onsite.

iTag analysis showed the biofilm contained abundant and diverse microorganisms, mostly affiliated with uncultured or cultivation-limited groups, including Promethearchaeota. New strains were isolated using a strategic batch-type cultivation method.

To evaluate growth temperature and substrate use, pure and tri-cultures of the strains were incubated at various temperatures. Substrate use was tested by supplementing basal media with sterilized substrates.

Epifluorescence microscopy and cell size measurements were conducted using a phase-contrast microscope. SEM and TEM were used to analyze cell structure and ultrastructure, revealing detailed morphological features.

Genomic and metabolic analyses were performed to determine the potential evolutionary significance of Promethearchaeota. The study highlights the importance of these archaea in understanding microbial evolution.