Iron metabolism in nitrogen fixers

In the tropical oceans, “fixed” nitrogen (in forms such as ammonium or nitrate) is scarce, so some cyanobacteria, such as those in the genus Trichodesmium, fix their own N from the abundant N2 gas by the nitrogenase enzyme complex.  However, due to the high Fe content of the nitrogenase Fe complex, the ability to fix N can be limited by Fe. Trichodesmium possessed putative Fe storage proteins such as bacterioferritin, which may play a role in storing Fe taken up from the environment during episodic dust inputs.   Also, the Fe-rich nitrogenase enzymes are recycled within Trichodesmium cells on a daily basis.  The Fe that is released must be properly maintained to avoid Fenton reaction-mediated oxidative stress. 

We are examining the putative dual roles of ferritin as an Fe storage protein under excessive environmental Fe concentrations (which occur episodically due to dust storms, see Dr. Yuan Gao’s page) and as a constitutively expressed protein that stores Fe after nitrogenase is degraded. 

Images upload in progress.