Genes encoding homologues of three consecutive enzymes in the butyrate/butanol-producing pathway ofClostridium acetobutylicumare clustered on theClostridium difficilechromosome

Screening of a Clostridium difficile lambda EMBL3 gene library with antisera raised against C. difficile culture supernatant identified several clones expressing a 31-kDa protein. A 1.8-kb HindIII fragment subcloned from one of the clones was sufficient for expression of the 31-kDa polypeptide. Southern blot analysis showed a region homologous to this fragment to be present in all of 13 different C. difficile strains tested. Sequence analysis of the 1.8-kb fragment revealed three adjacent open reading frames. A database search showed that these three open reading frames appeared to encode homologues of three consecutive enzymes in the butanol/butyrate-producing pathway of Clostridium acetobutylicum (crotonase, beta-hydroxybutyryl coenzyme A dehydrogenase and thiolase).