Involved in syntrophic growth of S.wolfei with butyrate, as part of the butyrate oxidation pathway. Probably catalyzes the hydration of crotonyl-CoA to 3-hydroxybutyryl-CoA. 3-hydroxybutanoyl-CoA = (2E)-butenoyl-CoA + H2O a short-chain (3S)-3-hydroxyacyl-CoA = a short-chain (2E)-enoyl-CoA + H2O Lipid metabolism; butanoate metabolism. Homotetramer. Highly expressed during syntrophic growth with butyrate (at protein level). Seems to be constitutively expressed. Belongs to the enoyl-CoA hydratase/isomerase family.