Genomics of the Resistance to Metal and Oxidative Stresses in Cyanobacteria

What is it about?

Cyanobacteria, the only known prokaryotes that perform oxygenic photosynthesis, are crucial for the biosphere, in using solar energy, water, carbon dioxide (CO2) and mineral salts to produce a large amount of oxygen (O2) and biomass for the food chain. Hence, cyanobacteria constitute the first biological barrier against the entry of toxic compounds into the food chain. Furthermore, cyanobacteria have the potential for the solar-driven, carbon-neutral, production of biofuels. However, cyanobacteria are often challenged by toxic reactive oxygen species generated under intense illumination, i.e. when they produce more photosynthetic electrons than what is needed for the assimilation of inorganic substrates. In requiring various metals for growth, cyanobacteria are also frequently affected by changes in metal availabilities, as well as by heavy metals, which are massively released in the environment by human industries, and constitute persistent pollutants because they cannot be degraded. Consequently, cyanobacteria have evolved elaborate mechanisms to regulate metal homeostasis and respond to heavy metals. These processes, which have been conserved during evolution, include (i) modification of the redox state of metal atoms to control their mobility; (ii) extracellular and intracellular sequestration; and (iii) active transport (uptake/export). In this review, we summarize the current knowledge concerning the cyanobacterial defenses against oxidative and metal stresses, emphasizing the well-studied strain Synechocystis PCC6803, and on the importance of the crosstalk between the glutathione detoxification system, iron-homeostasis and protection against oxidative and metal stresses.

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