| The bacterium Deinococcus radiodurans shows remarkable resistance to a range of damage caused by ionizing radiation, desiccation, UV radiation, oxidizing agents, and electrophilic mutagens. IrrE, a general DNA repair switch responsible for the extraordinary radioresistance of D. randiodurans, regulates stress response, energy metabolism, transcriptional regulation, signal transduction, protein turn-over and chaperoning pathways after irradiation. IrrE can increase the radioresistance and oxidation resistance of Escherichia coli. In addition, we found that IrrE enhanced multiple abotic resistance in E. coli and salt tolerance in plant. E. coli, as a model organism is well-suited to investigating regulation by IrrE. In this work, we investigate that IrrE can be utilized to improve tolerance to various abiotic stresses. Global transcriptome analysis showed that IrrE confers significantly enhanced salt tolerance and IrrE played a global regulatory role in gene expression in E. coli.We constructed plasmid pMG1-IrrE for expression of IrrE under control of a GroESL promoter in E. coli JM109. IrrE-expressing strain showed that IrrE significantly exhanced the tolerance to heat stress, acid stress, oxidative stress, osmotic stress, especially salt stress. Comparing with the control strain, the strain could normally grow in M9 medium supplemented with 0.65 M NaCl or in LB medium supplemented with 1 M NaCl. The ultrastructual changes of the cells observed by the transmission electron microscope (TEM) showed that the IrrE-expressing strain had normal cell morphology upon salt shock, whereas the control cells were largely plasmolysed: large periplasmic spaces and adhesion zones between the plasma membrane and the murein wall/outer membrane.To understand the effect of IrrE regulator on gene expression in E. coli, we used oligonucleotide arrays to delineate the transcriptiome difference between IrrE-expressing strain and control strain under control conditions and following 1M NaCl shock for 60min. The results showed that 307 genes and 5 small RNAs were up-regulated at least two-fold, while 134 genes and 1 small RNA were down-regulated more than two-fold under control condition in IrrE expressing strain comparing to control starin. And 654 genes and 9 small RNAs were up-regulated at least two-fold, while 240 genes and 2 small RNAs were down-regulated more than two-fold following salt shock. Among these differentially expressed genes, five major groups might contribute in various ways to the enhanced stress resistance:⑴Metabolism and growth related genes.⑵Transport and membrane related genes such as mscL encoding the large conductance mechanosensitive channel of the E. coli inner membrane that protects bacteria from lysis upon osmotic shock.⑶Regulation genes, including evgA, yhiE and yedO involoved in regulation of glutamate-dependent acid resistance.⑷Stress response genes such as the katE gene for the antioxidant defense mechanism.⑸DNA recombination and repair genes, including uvrC and mutL which protect cells from UV irradiation. Before salt shock, 71 of the IrrE-upregulated genes were also RpoS-dependent genes. Those genes include trehalose biosythesis genes otsAB, glutamate-dependent acid-resistance system genes gadABC and yhiO, as well as stress response genes bfr, dps, katE and osmBC. And the regulatory genes yhiO and functional genes gadABC of glutamate-dependent acid-resistance pathway were up-regulated in IrrE-expressing strains, which may contributes to acid resistance conferred by IrrE.Two osmotregulated trehalose synthesis genes, otsAB, were up-regulated while two trehalose dissimilation genes, treBC, were down-regulated, which may lead to trehalose accumulation in IrrE-expressing E. coli cells. After NaCl shock, the glycerol-degrading genes glpABC were down-regulated, which may result in osmoprotectants glycerol accumulation. In addition, some genes involved in metabolism and transport such as purN, flgH, fliO were repressed in control strains, which were up-regulated in IrrE-expressing strains under salt shock. Those results indicated IrrE may play a global regulator role in salt tolerance in E. coli.
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