How to overcome the problem of oxygen sensitivity of nitrogenase?

To overcome the problem of O2 sensitivity of nitrogenase, following strategies are involved:

1. A number of free- living nitrogen fixing organisms have mechanical, temporal, or biochemical barriers to separate the process of N2 fixation from aerobic metabolism i.e., compartmentalization.
2. Some organism like Cyanobacterium (oxygenic photosynthetic bacteria) have specialized cells called heterocyst that lack the O2 generating steps of photosynthesis.
3. Symbiotic diazotrophs like rhizobia associate with legumes. O2 is bound to leghemoglobin in the root nodules and thus supplied at a low rate that will not harm the nitrogenase.
4. In some plants, nodules can adjust their resistance to O2 diffusion by increasing or decreasing the number of cell layers around the nodulated roots.
5. In few rhizobial species, an O2 sensitive hemoprotein kinase, FixL which phosphorylates FixJ, which then activates and controls the expression of nif and fix genes. Thus when conditions are correct, Bacteroides will express nitrogenase.