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Antimicrobial Agents and Chemotherapy, March 2004, p. 930-939, Vol. 48, No. 3
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.3.930-939.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Two Sets of Paralogous Genes Encode the Enzymes Involved in the Early Stages of Clavulanic Acid and Clavam Metabolite Biosynthesis in Streptomyces clavuligerus

Kapil Tahlan,^* Hyeon Ung Park, Annie Wong, Perrin H. Beatty, and Susan E. Jensen

Department of Biological Sciences, University of Alberta, Edmonton T6G 2E9, Canada

Received 2 June 2003/ Returned for modification 30 September 2003/ Accepted 21 October 2003

Recently, a second copy of a gene encoding proclavaminate amidinohydrolase (pah1), an enzyme involved in the early stages of clavulanic acid and clavam metabolite biosynthesis in Streptomyces clavuligerus, was identified and isolated. Using Southern analysis, we have now isolated second copies of the genes encoding the carboxyethylarginine synthase (ceaS) and ß-lactam synthetase (bls) enzymes. These new paralogues are given the gene designations ceaS1 and bls1 and are located immediately upstream of pah1 on the chromosome. Furthermore, sequence analysis of the region downstream of pah1 revealed a second copy of a gene encoding ornithine acetyltransferase (oat1), thus indicating the presence of a cluster of paralogue genes. ceaS1, bls1, and oat1 display 73, 60, and 63% identities, respectively, at the nucleotide level to the original ceaS2, bls2, and oat2 genes from the clavulanic acid gene cluster. Single mutants defective in ceaS1, bls1, or oat1 were prepared and characterized and were found to be affected to variable degrees in their ability to produce clavulanic acid and clavam metabolites. Double mutants defective in both copies of the genes were also prepared and tested. The ceaS1/ceaS2 and the bls1/bls2 mutant strains were completely blocked in clavulanic acid and clavam metabolite biosynthesis. On the other hand, oat1/oat2 double mutants still produced some clavulanic acid and clavam metabolites. This may be attributed to the presence of the argJ gene in S. clavuligerus, which encodes yet another ornithine acetyltransferase enzyme that may be able to compensate for the lack of OAT1 and -2 in the double mutants.

Present address: National Cancer Institute, NIH, Bethesda, MD 20892.

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