Methanosarcina hadiensis strain:TD41E1-1 Genome sequencing. Methanosarcina hadiensis strain:TD41E1-1

Safe geological disposal of radioactive waste necessitates understanding of the geochemical dynamics and microbial activities that show an interplay with these dynamics. Previously, indications were found of active methanogenesis taking place in the deep subsurface habitat of Boom Clay pore water in Belgium. In this study, we set out to characterize this methanogenesis process using a culture-dependent approach. A distinct archaeal strain named TD41E1-1 was isolated from Boom Clay pore water and characterized geno- and phenotypically. Phylogenetic analysis demonstrated that isolate TD41E1-1 belongs to the Methanosarcina genus. TD41E1-1 cells are coccus-shaped and form aggregates in which cells are connected by very large extracellular appendages. Genomic analysis, as well as growth and substrate utilization experiments demonstrated that the strain prefers methylated compounds or hydrogen as substrates for methane production. Although it possesses a complete acetoclastic pathway, no methane was observed in the presence of acetate. Based on its phylogenetic relation to other known Methanosarcina species and on the presence of c-type cytochromes, it can be concluded that the strain likely occupies an intermediate position between type I and type II Methanosarcina species. Integration of the insights on physiological properties of strain TD41E1-1 into the prevailing geochemical model will enhance the understanding of crucial parameters such as the partial pressure of CO2 and pH within the confines of Boom Clay pore water. These are critical insights for the further investigation of secure geological disposal of radioactive waste in this environment.