Cobalt-precorrin-7 (C<sub>15</sub>)-methyltransferase (decarboxylating) (, CbiT) is an enzyme with systematic name S-adenosyl-L-methionine:precorrin-7 C<sub>15</sub>-methyltransferase (C<sub>12</sub>-decarboxylating). This enzyme catalyses the following chemical reaction
This enzyme catalyses both methylation at C-15 and decarboxylation of the C-12 acetate side chain of cobalt-precorrin-7 in the anaerobic pathway of adenosylcobalamin biosynthesis in bacteria such as Salmonella typhimurium, Bacillus megaterium, and Propionibacterium freudenreichii subsp. shermanii.