Osmosensitivity associated with insertions in argP (iciA) or glnE in glutamate synthase-deficient mutants of Escherichia coli
Authors: Rakesh S Laishram
J Gowrishankar
Madhusudan R Nandineni
Journal: Journal of bacteriology (2004)
Discipline: MICROBIOLOGY
Keywords: ampicillin enrichment; transposon insertion mutagenesis; NaCl-sensitive mutants; gltBD strain; osmotolerance
Affiliations: Centre for Cellular and Molecular Biology, Laboratory of Bacterial Genetics, Centre for DNA Fingerprinting and Diagnostics, Hyderabad, India

Abstract:  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. 

Retracted: No

PubPeer comments:
 Duplicated images under different labels with different exposure contrast settings. ![file] , 
 #1 We wish to thank the reader for pointing out this error, which was inadvertent. We have submitted the following text to the Journal of Bacteriology with the request that it be published as an Author Correction. Author Correction Volume 186, no.19, p.6391-6399, 2004, https: doi.org 10.1128 JB.186.19.6391-6399.2004 Page 6395, Fig.2: The panel located at third from left on the top row is a duplicate of that at fourth from left on the bottom row. It appears that the same image was erroneously used twice when the figure was assembled. Although the original images are now lost, the strains (GJ4663 and GJ4652 pBR329, respectively) are available in our collection and we have established that the results as depicted in the figure are reproducible. Hence, the figure error does not in any way alter the interpretations or conclusions drawn in the paper. , 
 The authors in their response state that they have established the results as depicted in the contested (duplicated) image, but they did not append any new data in support of that. In the published erratum, they just mention that they have the strains in their collection although they lost the original images ). So, then, on whom is the onus of reproducing those data? And also explaining as to how the results and discussion of their findings are unaffected by this duplication. , 
 In consultation with the Editors, a correction has already been published in the Journal. The authors of the paper do not wish to add anything further in response. ,