Methanosarcina mazei Go1 wild type was transformed with a Cas1solo (MM_RS16885) overexpression plasmid. A single positive colony was isolated, named Methanosarcina mazei mutant 208 (Mm Mut 208), and used during a long-term evolution experiment. As a reference for possible chromosomal mutations or rearrangements during the long-term experiment, strain Mm Mut 208 was sequenced using Illumina and Oxford Nanopore Sequencing and assembled using hybrid assembly.