Provided herein is an isolated Methanothermobacter microorganism that is (a) a microorganism of Methanothermobacter thermautotrophicus strain UC 120910, deposited on Dec. 21, 2010, with the American Type Culture Collection (ATCC) under ATCC® Patent Deposit Designation No. PTA-11561, (b) a variant of the microorganism of Methanothermobacter thermautotrophicus strain UC 120910, or (c) a progeny of the microorganism of Methanothermobacter thermautotrophicus strain UC 120910, wherein the variant or progeny retains the phenotypic characteristics of the microorganism of Methanothermobacter thermautotrophicus strain UC 120910. Also provided herein is a substantially pure culture or monoculture comprising the Methanothermobacter microorganism of the disclosure. A system for converting electric power into methane, comprising a biological reactor having at least a cathode, an anode, a presently disclosed Methanothermobacter microorganism, water, and carbon dioxide, and method of using the system for converting electricity into methane are further provided herein.