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Journal of Bacteriology, September 2000, p. 5180-5187, Vol. 182, No. 18
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Lesions in gshA (Encoding gamma -L-Glutamyl-L-Cysteine Synthetase) Prevent Aerobic Synthesis of Thiamine in Salmonella enterica Serovar Typhimurium LT2

Jeffrey Gralnick, Eric Webb,dagger Brian Beck,Dagger and Diana Downs*

Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin 53706

Received 18 April 2000/Accepted 3 July 2000

Thiamine pyrophosphate is an essential cofactor that is synthesized de novo in Salmonella enterica serovar Typhimurium and other bacteria. In addition to genes encoding enzymes in the biosynthetic pathway, mutations in other metabolic loci have been shown to prevent thiamine synthesis. The latter loci identify the integration of the thiamine biosynthetic pathway with other metabolic processes and can be uncovered when thiamine biosynthesis is challenged. Mutations in gshA, encoding gamma -L-glutamyl-L-cysteine synthetase, prevent the synthesis of glutathione, the major free thiol in the cell, and are shown here to result in a thiamine auxotrophy in some of the strains tested, including S. enterica LT2. Phenotypic characterization of the gshA mutants indicated they were similar enough to apbC and apbE mutants to warrant the definition of a class of mutants unified by (i) a requirement for both the hydroxymethyl pyrimidine (HMP) and thiazole (THZ) moiety of thiamine, (ii) the ability of L-tryosine to satisfy the THZ requirement, (iii) suppression of the thiamine requirement by anaerobic growth, and (iv) suppression by a second-site mutation at a single locus. Genetic data indicated that a defective ThiH generates the THZ requirement in these strains, and we suggest this defect is due to a reduced ability to repair a critical [Fe-S] cluster.

* Corresponding author. Mailing address: University of Wisconsin-Madison, 1550 Linden Dr., Madison, WI 53706. Phone: (608) 265-4630. Fax: (608) 262-9865. E-mail: downs{at}macc.wisc.edu.

dagger Present address: Biology Department, The Woods Oceanographic Institute, Woods Hole, MA 02543.

Dagger Present address: Department of Microbiology, University of Minnesota, Minneapolis, MN 55455.

Journal of Bacteriology, September 2000, p. 5180-5187, Vol. 182, No. 18
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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