Physiological and genomic characterization of Methanothermobacter thermautotrophicus strain Z-73A, an isolate from deep underground.

Underground biomethanation represents a promising solution for green energy storage. An isolate of Methanothermobacter thermautotrophicus was obtained in previous study from an underground gas reservoir where it played a key role in a successful in-situ biomethanation experiment. In this study, the physiological and environmental tolerances of the strain are characterised. Optimal methane evolution rates were observed at 55-65 °C and pH 6.5-7.0, methane production was significantly increased by agitation (up to 2.29 mmol CH4·h-1·L-1). The strain showed higher tolerance to NH4Cl (up to 0.6 M) than to NaCl (optimal 0.04-0.4 M). The strain was also tested for its resistance to silver nanoparticles. The whole-genome sequence of the strain was determined, and the corrosion potential was evaluated. To visualise the cells, Scanning Electron Microscopy (SEM) and a method of Advanced Environmental Scanning Electron Microscopy (A-ESEM) were used. These findings describe the behaviour of M.thermautotrophicus under suboptimal conditions and highlight the need for further optimization to improve methane production yields.