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Genome-wide transcriptional responses of Escherichia coli K-12 to continuous osmotic and heat stresses.

ABSTRACT: Osmotic stress is known to increase the thermotolerance and oxidative-stress resistance of bacteria by a mechanism that is not adequately understood. We probed the cross-regulation of continuous osmotic and heat stress responses by characterizing the effects of external osmolarity (0.3 M versus 0.0 M NaCl) and temperature (43 degrees C versus 30 degrees C) on the transcriptome of Escherichia coli K-12. Our most important discovery was that a number of genes in the SoxRS and OxyR oxidative-stress regulons were up-regulated by high osmolarity, high temperature, or a combination of both stresses. This result can explain the previously noted cross-protection of osmotic stress against oxidative and heat stresses. Most of the genes shown in previous studies to be induced during the early phase of adaptation to hyperosmotic shock were found to be also overexpressed under continuous osmotic stress. However, there was a poorer overlap between the heat shock genes that are induced transiently after high temperature shifts and the genes that we found to be chronically up-regulated at 43 degrees C. Supplementation of the high-osmolarity medium with the osmoprotectant glycine betaine, which reduces the cytoplasmic K(+) pool, did not lead to a universal reduction in the expression of osmotically induced genes. This finding does not support the hypothesis that K(+) is the central osmoregulatory signal in Enterobacteriaceae.

SUBMITTER: Gunasekera TS

PROVIDER: S-EPMC2395010 | biostudies-literature | 2008 May

REPOSITORIES: biostudies-literature

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Genome-wide transcriptional responses of Escherichia coli K-12 to continuous osmotic and heat stresses.

Gunasekera Thusitha S TS Csonka Laszlo N LN Paliy Oleg O

Journal of bacteriology 20080321 10

Osmotic stress is known to increase the thermotolerance and oxidative-stress resistance of bacteria by a mechanism that is not adequately understood. We probed the cross-regulation of continuous osmotic and heat stress responses by characterizing the effects of external osmolarity (0.3 M versus 0.0 M NaCl) and temperature (43 degrees C versus 30 degrees C) on the transcriptome of Escherichia coli K-12. Our most important discovery was that a number of genes in the SoxRS and OxyR oxidative-stress ...[more]

PMID: 18359805

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Project description:We probed the mechanism of cross-regulation of osmotic and heat stress responses by characterizing the effects of high osmolarity (0.3M vs. 0.0M NaCl) and temperature (43oC vs. 30oC) on the transcriptome of Escherichia coli K12 using E. coli Genome 2 Array (Affymetrix, Inc.). Independent array hybridizations were carried out for 3 biological replicates (independent cultures). Total RNA was extracted using a hot phenol-chloroform method. cDNA synthesis, fragmentation and labeling, and washing and scanning of E. coli GeneChip Arrays were performed according to the instructions of the manufacturer (Affymetrix Technical Manual, Affymetrix, Inc., USA). Labeled cDNA was hybridized to E. coli Genome 2 Array (Affymetrix, Inc.). Independent array hybridizations were carried out for 3 biological replicates (independent cultures) of each condition. A number of genes in the SoxRS and OxyR oxidative stress regulons were up-regulated by high osmolarity, high temperature, and/or by the combination of both stresses. This result could account for cross-protection of osmotic stress against oxidative stress. The trehalose biosynthetic genes were induced by both stresses, in accord with the proposed protective role of this disaccharide against thermal and oxidative damage. Experiment Overall Design: E. coli K12 strain NCM3722 cultures were grown with aeration in K medium containing 10 or 20 mM glucose. To impose osmotic stress, the osmolarity of the medium was increased to 0.64 osm by supplementation with 0.3 M NaCl. Because E. coli is a methionine auxotroph above 42oC the K medium cultures were supplemented with 0.5 mM methionine. Glycine betaine (GB) was added to the high osmolarity media to a final concentration of 1 mM. Cells taken from a single colony on LB agar were inoculated into 1ml liquid LB and grown to saturation at 37oC, then 0.05 ml were inoculated into i) K medium, 0.5 mM methionine, 10 mM glucose; ii) K medium, 0.5 mM methionine, 10 mM glucose, 0.3 M NaCl; and iii) K medium, 0.5 mM methionine, 10 mM glucose, 0.3 M NaCl, 1 mM GB. The cultures were grown to saturation at 30oC and 43oC, and sub-cultured once into the same medium and grown at the same temperatures as before. Exponentially growing cells form these cultures were then inoculated into Erlenmeyer flasks (starting OD600nm 0.05) containing 40 ml of the same medium, and incubated in the same salt and temperature conditions as used previously, except that the glucose concentration was increased to 20 mM. When the cells reached OD600nm of 0.4-0.5 (~3 doublings), 25 ml were added to a 2.5 ml mixture of cold 95% ethanol and 5% phenol to preserve RNA. The cells were cooled briefly on ice, immediately harvested by centrifugation (4oC), and the pellet was frozen on dry ice. The six different growth conditions used were: C1 - 30oC, no NaCl; C2: 30oC, 0.3 M NaCl; C3: 30oC, 0.3 M NaCl, 1 mM GB; C4: 43oC, no NaCl; C5: 43oC, 0.3 M NaCl; C6: 43oC, 0.3 M NaCl, 1 mM GB.

Dataset Information

Genome-wide transcriptional responses of Escherichia coli K-12 to continuous osmotic and heat stresses.

Publications

Genome-wide transcriptional responses of Escherichia coli K-12 to continuous osmotic and heat stresses.

Similar Datasets

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