PROPANEDIOL UTILIZATION GENES (PDU) OF SALMONELLA-TYPHIMURIUM - 3 GENES FOR THE PROPANEDIOL DEHYDRATASE

The propanediol utilization (pdu) operon of Salmonella typhimurium enc odes proteins required for the catabolism of propanediol, including a coenzyme B-12-dependent propanediol dehydratase. A clone that expresse s propanediol dehydratase activity was isolated from a Salmonella geno mic library. DNA sequence analysis showed that the clone included part of the pduF gene, the pduABCDE genes, and a long partial open reading frame (ORF1). The clone included 3.9 kbp of pdu DNA which had not bee n previously sequenced. Complementation and expression studies,vith su bclones constructed via PCR showed that three genes (pduCDE) are neces sary and sufficient for propanediol dehydratase activity. The function of ORF1 was not determined. Analyses showed that the S. typhimurium p ropanediol dehydratase was related to coenzyme B-12-dependent glycerol dehydratases from Citrobacter freundii and Klebsiella pneumoniae. Une xpectedly, the S. typhimurium propanediol dehydratase was found to be 98% identical in amino acid sequence to the Klebsiella oxytoca propane diol dehydratase; this is a much higher identity than expected, given the relationship between these organisms. DNA sequence analyses also s upported previous studies indicating that the pdu operon was inherited along with the adjacent cobalamin biosynthesis operon by a single hor izontal gene transfer.