Coenzyme A-transferase that converts butyrate to butyryl-CoA. Involved in the syntrophic growth of S.wolfei on butyrate in cooperation with methanogens or an appropriate hydrogen-scavenging bacterium, as part of the butyrate oxidation pathway. acetyl-CoA + butanoate = acetate + butanoyl-CoA Lipid metabolism; butanoate metabolism. Expressed during syntrophic growth with butyrate (at protein level). Seems to be constitutively expressed. Belongs to the acetyl-CoA hydrolase/transferase family.