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Journal of Bacteriology, October 2004, p. 6391-6399, Vol. 186, No. 19
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.19.6391-6399.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Osmosensitivity Associated with Insertions in argP (iciA) or glnE in Glutamate Synthase-Deficient Mutants of Escherichia coli

Madhusudan R. Nandineni,1,2 Rakesh S. Laishram,2 and J. Gowrishankar2*

Centre for Cellular and Molecular Biology,1 Laboratory of Bacterial Genetics, Centre for DNA Fingerprinting and Diagnostics, Hyderabad, India2

Received 1 April 2004/ Accepted 7 July 2004

An ampicillin enrichment strategy following transposon insertion mutagenesis was employed to obtain NaCl-sensitive mutants of a gltBD (glutamate synthase [GOGAT]-deficient) strain of Escherichia coli. It was reasoned that the gltBD mutation would sensitize the parental strain even to small perturbations affecting osmotolerance. Insertions conferring an osmosensitive phenotype were identified in the proU, argP (formerly iciA), and glnE genes encoding a glycine betaine/proline transporter, a LysR-type transcriptional regulator, and the adenylyltransferase for glutamine synthetase, respectively. The gltBD+ derivatives of the strains were not osmosensitive. The argP mutation, but not the glnE mutation, was associated with reduced glutamate dehydrogenase activity and a concomitant NH4+ assimilation defect in the gltBD strain. Supplementation of the medium with lysine or a lysine-containing dipeptide phenocopied the argP null mutation for both osmosensitivity and NH4+ assimilation deficiency in a gltBD background, and a dominant gain-of-function mutation in argP was associated with suppression of these lysine inhibitory effects. Osmosensitivity in the gltBD strains, elicited either by lysine supplementation or by introduction of the argP or glnE mutations (but not proU mutations), was also correlated with a reduction in cytoplasmic glutamate pools in cultures grown at elevated osmolarity. We propose that an inability to accumulate intracellular glutamate at high osmolarity underlies the osmosensitive phenotype of both the argP gltBD and glnE gltBD mutants, the former because of a reduction in the capacity for NH4+ assimilation into glutamate and the latter because of increased channeling of glutamate into glutamine.

* Corresponding author. Mailing address: Laboratory of Bacterial Genetics, Centre for DNA Fingerprinting and Diagnostics, ECIL Road, Nacharam, Hyderabad 500 076, India. Phone: 91-40-27155609. Fax: 91-40-27155610. E-mail: shankar{at}cdfd.org.in.

Journal of Bacteriology, October 2004, p. 6391-6399, Vol. 186, No. 19
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.19.6391-6399.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Bouvier, J., Stragier, P., Morales, V., Remy, E., Gutierrez, C. (2008). Lysine Represses Transcription of the Escherichia coli dapB Gene by Preventing Its Activation by the ArgP Activator. J. Bacteriol. 190: 5224-5229 [Abstract] [Full Text]  
  • Goss, T. J. (2008). The ArgP Protein Stimulates the Klebsiella pneumoniae gdhA Promoter in a Lysine-Sensitive Manner. J. Bacteriol. 190: 4351-4359 [Abstract] [Full Text]  
  • Yan, D. (2007). Protection of the glutamate pool concentration in enteric bacteria. Proc. Natl. Acad. Sci. USA 104: 9475-9480 [Abstract] [Full Text]  
  • Laishram, R. S., Gowrishankar, J. (2007). Environmental regulation operating at the promoter clearance step of bacterial transcription. Genes Dev. 21: 1258-1272 [Abstract] [Full Text]  


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