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J. Bacteriol., 01 1995, 390-400, Vol 177, No. 2
JA Gutierrez and LN Csonka
Mutants of Salmonella typhimurium that were not protected by glycine
betaine (GB) but could still use proline as an osmoprotectant in media of
high osmolality were isolated. The mutations responsible for this phenotype
proved to be alleles of the adenylate kinase (adk) gene, as shown by
genetic mapping, sequencing of the cloned mutant alleles, complementation
with the Escherichia coli adk gene, and assay of Adk enzyme activity in
crude extracts. One of the mutations was in the untranslated leader of the
adk mRNA, a second was in the putative Shine- Dalgarno sequence, and a
third was in the coding region of the gene. The loss of osmoprotection by
GB was shown to be due to the fact that the accumulation of this solute
actually resulted in a severe inhibition of growth in the adk mutants. The
addition of GB in the presence of 0.5 M NaCl resulted in a rapid decline in
the ATP pool and a dramatic increase in the AMP pool in the mutants.
Proline, which is not toxic to the adk mutants, did not have any
significant effects on the cellular levels of ATP and AMP. The mutants
exhibited two different phenotypes with respect to the utilization of other
osmoprotectants: they were also inhibited by propiothiobetaine,
L-carnitine, and gamma- butyrobetaine, but they were stimulated normally in
media of high osmolality by proline, choline-O-sulfate, and stachydrine.
Copyright © 1995, American Society for Microbiology
Isolation and characterization of adenylate kinase (adk) mutations in Salmonella typhimurium which block the ability of glycine betaine to function as an osmoprotectant
Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-1392.
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