Genomics of the Pleïotropic Glutathione System in Cyanobacteria

Abstract Cyanobacteria, only prokaryotes capable of oxygenic photosynthesis, are fascinating microorganisms that are logically attracting a growing attention in various areas of basic and applied researches. Cyanobacteria have colonized most water and soil environments. Consequently, they support a large part of life on Earth in renewing the oxygenic atmosphere and making up organic assimilates for the food chain. Furthermore, cyanobacteria are regarded as promising ‘low-cost’ microbial cell factories for carbon capture and storage, and the sustainable production of biofuels, thanks to their (1) simple nutritional requirements, (2) physiological robustness, (3) metabolic plasticity, and (iv) the powerful genetics of some model strains. Because of their photoautotrophic lifestyle, cyanobacteria are inevitably challenged by toxic reactive oxygen species generated by photosynthesis (and respiration), especially under intense illumination when the light-driven electron transport exceeds what needed for the assimilation of inorganic substrates. This review summarizes what is known regarding the defences against oxidative stress in cyanobacteria, emphasizing on the central role of glutathione and the wealth of glutathione-dependent enzymes, which have been well conserved throughout evolution. We also report on what can be inferred in this field by mining the information provided by the 70 sequenced genomes of morphologically and physiologically diverse cyanobacteria.