A novel redox-sensing regulator OcsR controls antimicrobial resistance in Corynebacterium glutamicum

Redox-sensing regulators are crucial for bacterial adaptation to environmental stress. In the model organism Corynebacterium glutamicum , while TetR (tetracycline repressor)-family proteins are known for ligand-mediated regulation, thiol-based oxidative stress sensing by this family remains poorly understood. This study characterizes OcsR (oxidative and copper stress-sensing regulator), a novel redox-sensitive TetR-family member conserved in corynebacteria . Transcriptomics revealed that OcsR deletion alters several important cellular processes, including iron metabolism, antimicrobial resistance and carbohydrate metabolism. We demonstrate that OcsR ( Cg0454 ) is the first gene of an operon, co-transcribed with downstream genes cg0455 and cg0456 encoding two major facilitator superfamily (MFS) proteins. OcsR directly negatively regulates the expression of its own operon. OcsR as a dimer binds two imperfect palindromic sequences far downstream of its operon's transcriptional start site. This DNA-binding activity is specifically inhibited by copper (II) and hydroxyl radical (·OH), which triggers disulfide cross-linking between the OcsR's redox-active cysteine residues. This cross-linking results in OscR inactivation, relieving the repression of its own operon and thus to the upregulation of the multidrug resistance MFS proteins Cg0455 and Cg0456. This was correlated with an enhanced tolerance to antibiotics that are more efficiently expelled from the cell as well as to a reduced tolerance to heavy metals (iron (II) and copper (II) and the dysregulation of iron homeostasis. Interestingly, vancomycin, iron (II) and ethidium bromide that stimulated reactive ·OH production and/or free copper release significantly induced the expression of the OcsR operon. C. glutamicum OcsR is a redox-sensing regulator that employs a reversible thiol switch to perceive antibiotic and toxic metal-triggered oxidative stress, directly linking environmental cues to a protective transcriptional response.