Converts cyanocobalamin (CN-B12) to adenosylcobalamin (AdoCbl), the inducer of the eut operon (PubMed:15516577, PubMed:16636051, PubMed:24336938). Is not active on cobinamide nor other intermediates in the adenosylcobalamin synthetic pathway. Allows full induction of the eut operon (PubMed:15516577). Can use ADP, CTP and dATP in place of ATP, and cobinamide in place of cobalamin, none are as efficiently used as ATP and cobalamin (PubMed:16636051). Expression of the eut operon allows this bacteria to use ethanolamine (EA) as a carbon, nitrogen and energy source. It relies on cobalamin (vitamin B12) both as a cofactor for the ethanolamine ammonia-lyase (EAL) activity and to induce the operon (PubMed:3045078). EA enhances bacterial survival in macrophages in a concentration-dependent manner, suggesting it is an important nutrient during infection (PubMed:29531136). 2 ATP + 2 cob(II)inamide + 2 H2O + reduced [electron-transfer flavoprotein] = 2 adenosylcob(III)inamide + 2 diphosphate + 3 H(+) + oxidized [electron-transfer flavoprotein] + 2 phosphate ATP + cob(I)alamin-[corrinoid adenosyltransferase] = adenosylcob(III)alamin + apo-[corrinoid adenosyltransferase] + triphosphate Binds 1 divalent metal cation ion per homodimer with both subunits providing Cys ligands; Fe(2+) gives most activity and is possibly the physiological cofactor, followed by Zn(2+) and Co(2+) (PubMed:24336938, PubMed:28045498). Activity stimulated by Mn(2+) (PubMed:16636051). kcat is 0.03 sec(-1). Optimum pH is 7.0. Amine and polyamine degradation; ethanolamine degradation. Homodimer. Part of the 17-gene eut operon transcribed from a single promoter, induced by ethanolamine and adenosylcobalamin (AdoCbl, vitamin B12). A quadruple eutP-eutQ-eutT-eutD deletion is not impaired for aerobic growth on ethanolamine (EA) supplemented with cobalamin (vitamin B12) (PubMed:10464203). Can grow on EA as sole carbon source when AdoB12 is supplied; double cobA-eutT mutants do not grow with CN-B12 as a nitrogen source (PubMed:15516577). A non-polar deletion mutant grows on EA from pH 5.5 to pH 8.0, but does not grow at pH 8.5, no change in acetaldehyde release on EA plus vitamin B12 (PubMed:16585748). Belongs to the Cob(I)alamin adenosyltransferase family. EutT subfamily.