In addition to directly limiting primary production in some oceanic regions, iron is thought to limit it indirectly in many other regions by controlling the input of fixed nitrogen. This is because the nitrogenase enzyme, which is responsible for dinitrogen (N2) fixation, requires a lot of Fe. The most important nitrogen fixer in the sea, the cyanobacterium Trichodesmium, thrives in tropical and subtropical regions where iron inputs from atmospheric dust are highly episodic. We have thus been studying the mechanism of Fe storage in Trichodesmium. As a first step, we have identified, isolated, over-expressed and partially characterized a Dps protein (DNA-binding protein from starved cells) from this organism (Castruita et al. 2006). This protein, the first Fe storage protein isolated from a marine microbe, is able to store vast quantities of Fe; it is also able to bind to DNA and protect it from degradation. This second attribute may be important to protect the genetic material of the organism during periods of dormancy when nutrient concentrations are low or other environmental conditions are unfavorable.
