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Journal of Bacteriology, January 2004, p. 270-277, Vol. 186, No. 2
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.2.270-277.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Isolation and Characterization of Burkholderia cenocepacia Mutants Deficient in Pyochelin Production: Pyochelin Biosynthesis Is Sensitive to Sulfur Availability

Kate L. Farmer and Mark S. Thomas^*

Division of Genomic Medicine, School of Medicine and Biomedical Sciences, University of Sheffield, Sheffield S10 2RX, United Kingdom

Received 4 August 2003/ Accepted 13 October 2003

The opportunistic pathogen Burkholderia cenocepacia produces the yellow-green fluorescent siderophore, pyochelin. To isolate mutants which do not produce this siderophore, we mutagenized B. cenocepacia with the transposon mini-Tn5Tp. Two nonfluorescent mutants were identified which were unable to produce pyochelin. In both mutants, the transposon had integrated into a gene encoding an orthologue of CysW, a component of the sulfate/thiosulfate transporter. The cysW gene was located within a putative operon encoding other components of the transporter and a polypeptide exhibiting high homology to the LysR-type regulators CysB and Cbl. Sulfate uptake assays confirmed that both mutants were defective in sulfate transport. Growth in the presence of cysteine, but not methionine, restored the ability of the mutants to produce pyochelin, suggesting that the failure to produce the siderophore was the result of a depleted intracellular pool of cysteine, a biosynthetic precursor of pyochelin. Consistent with this, the wild-type strain did not produce pyochelin when grown in the presence of lower concentrations of sulfate that still supported efficient growth. We also showed that whereas methionine and certain organosulfonates can serve as sole sulfur sources for this bacterium, they do not facilitate pyochelin biosynthesis. These observations suggest that, under conditions of sulfur depletion, cysteine cannot be spared for production of pyochelin even under iron starvation conditions.

Present address: Research Support and Commercialisation Office, University of Nottingham, University Park NG7 2RD, United Kingdom.

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