Bacteria are permanently in contact with reactive oxygen species (ROS), both over the course of their life cycle as well that present in their environment. These species cause damage to proteins, lipids, and nucleotides, negatively impacting the organism. To detect these ROS molecules and to stimulate the expression of proteins involved in antioxidative stress response, bacteria use a number of different protein-based regulatory and sensory systems. ROS-based stress detection mechanisms induce posttranslational modifications, resulting in overall conformational and structural changes within sensory proteins. The subsequent structural rearrangements result in changes of protein activity, which lead to regulated and appropriate response on the transcriptional level. Many bacterial enzymes and regulatory proteins possess a conserved signature, the zinc-containing redox centre Cys-X-X-Cys in which a disulfide bridge is formed upon oxidative stress. Other metal-dependent oxidative modifications of amino acid side-chains (dityrosines, 2-oxo-histidines, or carbonylation) also modulate the activity of redox-sensitive proteins. Using molecular biology, biochemistry, biophysical, and structure biology tools, molecular mechanisms involved in sensing and response to oxidative stress have been elucidated in detail. In this review, we analyze some examples of bacterial redox-sensing proteins involved in antioxidative stress response and focus further on the currently known molecular mechanism of function. 1. Introduction Interference in the balance between the environmental production of reactive oxygen species (ROS), including hydroxyl radicals (？OH) and hydrogen peroxide (H2O2), and the ability of biological systems to readily detect and detoxify them, or repair the resulting damage, are defined as oxidative stress. Highly reactive radicals cause the oxidative damage of different macromolecules—proteins, DNA, and lipids—leading to loss of function, an increased rate of mutagenesis, and ultimately cell death. In humans, for example, oxidative stress is involved in many diseases, such as rheumatoid arthritis, autoinflammatory diseases, neurodegenerative diseases, and cancer [1, 2]. However, the production of some ROS (e.g., ？OH) can also be beneficial, as they are used by the human immune system to attack and kill pathogens, such as the production of ROS by macrophages. Additionally, H2O2 is an important signalling molecule that participates in redox signalling [3]. Sensing of ROS-mediated signals also plays a crucial role in the biology of microorganisms. Bacteria,
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