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.
-L-Glutamyl-L-Cysteine Synthetase) Prevent
Aerobic Synthesis of Thiamine in Salmonella enterica Serovar
Typhimurium LT2

andDepartment 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
-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.
Present address: Biology Department, The Woods Oceanographic
Institute, Woods Hole, MA 02543.
Present address: Department of Microbiology, University of
Minnesota, Minneapolis, MN 55455.
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