Erin is studying the regulation of nitrogenase in Rhodopseudomonas palustris. R. palustris produces hydrogen via nitrogenase, using light energy and electrons from reduced carbon sources.  Nitrogenase is a costly enzyme to synthesize and operate.  To save energy, the bacterium controls nitrogenase expression and activity very tightly, especially in response to fixed nitrogen sources such as ammonia.  Along with Dr. Federico Rey, Erin described several mutants of R. palustris which produce hydrogen in the presence of ammonia.  These mutations occur in NifA, the master regulator of nitrogen fixation genes, and cause the constitutive expression of nitrogenase.  She is currently investigating why nitrogenase is not post-translationally inactivated when expressed by mutant NifA in the presence of ammonium.  She is also investigating the regulation of the two alternative nitrogenases encoded on the R. palustris genome.  The goal of this research is to understand how nitrogenase is controlled by the cell so that these controls may be circumnavigated for increased hydrogen production.