Methyltransferase able to catalyze the transfer of a methyl group from methylcobalamin (methylCbl) to tetrahydrofolate (THF) in vitro, to generate methyl-THF and cob(I)alamin. In vivo, the methyl group probably comes from the adjacently encoded methylated corrinoid protein DSY3155. The methyl group may then be ultimately converted to carbon dioxide, and its oxidation would also provide reducing equivalents for anaerobic respiration. Thus, may function in the pathway that allows anaerobic methylotrophic growth of D.hafniense using glycine betaine. Belongs to the MtrH family.