Abstract
BackgroundCssR, the product of the Corynebacterium glutamicum ncgl1578 gene cotranscribed with ncgl1579, is a TetR (tetracycline regulator) family repressor. Although many TetR-type regulators in C. glutamicum have been extensively described, members of the TetR family involved in the stress response remain unidentified.ResultsIn this study, we found that CssR regulated the transcription of its own gene and the ncgl1576-ncgl1577 operon. The ncgl1576-ncgl1577 operon, which is located upstream of cssR in the orientation opposite that of the cssR operon, encodes an ATP-binding cassette (ABC), some of which are involved in the export of a wide range of antimicrobial compounds. The cssR-deletion (ΔcssR) mutant displayed increased resistance to various stresses. An imperfect palindromic motif (5′-TAA(G)TGN13CA(G)TTA-3′; 25 bp) located at the intergenic region between cssR and ncgl1577 was identified as the sole binding site for CssR. Expression of cssR and ncgl1577 was induced by antibiotics and heavy metals but not H2O2 or diamide, and the DNA-binding activity of CssR was impaired by antibiotics and heavy metals but not H2O2. Antibiotics and heavy metals caused CssR dissociation from target gene promoters, thus derepressing their transcription. Oxidant treatment neither altered the conformation of CssR nor modified its cysteine residues, indicating that the cysteine residues in CssR have no redox activity. In the ΔcssR mutant strain, genes involved in redox homeostasis also showed increased transcription levels, and the NADPH/NADP+ ratio was higher than that of the parental strain.ConclusionThe stress response mechanism of CssR in C. glutamicum is realized via ligand-induced conformational changes of the protein, not via cysteine oxidation-based thiol modification. Moreover, the crucial role of CssR in the stress response was demonstrated by negatively controlling the expression of the ncgl1576-ncgl1577 operon, its structural gene, and/or redox homeostasis-related genes.
Highlights
CssR, the product of the Corynebacterium glutamicum ncgl1578 gene cotranscribed with ncgl1579, is a Tetracycline repressor (TetR) family repressor
The TetR‐type regulator CssR was conserved in corynebacteria It has been reported that TetR family regulators function as negative regulators of physiological processes such as efflux pumping and biosynthesis of antibiotics, osmotic stress, and solvent resistance [28]
A sequence comparison showed that CssR putative homologs were present in several species of the genus Corynebacterium, such as C. deserti, C. crudilactis, C. callunae, and C. halotolerans (Additional file 1: Figure S1a)
Summary
CssR, the product of the Corynebacterium glutamicum ncgl1578 gene cotranscribed with ncgl1579, is a TetR (tetracycline regulator) family repressor. Many TetR-type regulators in C. glutamicum have been extensively described, members of the TetR family involved in the stress response remain unidentified. Corynebacterium glutamicum, a well-known l-amino acid producer in industry and a model organism for systems biology, unavoidably generates or encounters a series of unfavorable circumstances during fermentation [1, 2], including pH and temperature fluctuations, osmotic variation, and nutrient shortages. Diverse environments inevitably produce excessive reactive oxygen species (ROS) [3]. The defense systems of C. glutamicum against stress-causing factors have attracted considerable attention from scientists, and their molecular mechanisms are being revealed. Corynebacterium glutamicum shows strong survivability that is attributed to two elaborate defense mechanisms, including enzymatic and nonenzymatic systems
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