Involved in the biosynthesis of the osmoprotectant glycine betaine from choline. choline + NAD(+) = betaine aldehyde + H(+) + NADH Amine and polyamine biosynthesis; betaine biosynthesis via choline pathway; betaine aldehyde from choline (dehydrogenase route): step 1/1. Appears to be translated from two alternative initiation sites, at least when overexpressed in E.coli. By choline and by high osmolarity in the presence of choline (PubMed:8752328, PubMed:22408163). Repressed by GbsR (PubMed:22408163). Deletion of the gbsAB genes abolishes the choline-glycine betaine synthesis pathway and the ability of B.subtilis to deal effectively with high-osmolarity stress in choline- or glycine betaine aldehyde-containing medium. Belongs to the iron-containing alcohol dehydrogenase family. Truncated N-terminus.