**2. Classical strategies to overcome iron starvation situations**

Cyanobacteria evolved very efficient mechanisms to cope with iron deficiency. Iron deprivation triggers a variety of responses that range from upregulation of the iron acquisition systems to reduction or substitution of structures or molecules. At the physiological level, Strauss [18] categorized the responses as retrenchment (reduction of cell size, loss of phycobilisomes, ultrastructural changes and pigment changes), compensation (as the synthesis of flavodoxin, playing ferredoxin role, expression of *isiA* gene) and acquisition (induction of iron acquisition systems). Accommodation to iron deficiency requires changes in the expression of a large number of genes of many metabolic pathways, some of them not obviously related with iron metabolism, such as respiration, photosynthesis, nitrogen metabolism, glycolysis, tricarboxylic acids cycle, amino acid synthesis, synthesis of toxins and antioxidant defenses. Those changes highlight the responses associated to iron deficiency [9, 19]. It is important to consider that the responses are going to be different depending on the stress threshold: moderate, severe or extreme.
