The Nitrophenol compounds are used as intermediates in the production of pharmaceuticals, dyes, pesticides, wood preservatives and explosives. 2,4-dinitrophenol (2,4-DNP) is a toxic and persistent pollutant compound considered a priority by the Agency for Environmental Protection (EPA). Is selected Rhodobacter capsulatus B10S bacterial strain belonging to the group of the red photosynthetic bacteria (Rhodospirillales), this organism fotorreduce 2,4-dinitrophenol, 2-amino-4-nitrophenol (ANP) under anaerobic conditions, using a nitrophenol reductase activity which is induced in the presence of nitrophenols and repressed in cells cultured with ammonium. 2,4-DNP is an uncoupling energy that strongly inhibits nitrogen fixation in R. capsulatus. In fact, this bacteria can only grow diazotrofically (nitrogen fixation conditions) when the 2,4-DNP has become almost entirely in ANP. The aim of this study is to determine the differential expression of proteins (induction, repression, overexpression) by two-dimensional electrophoresis R. capsulatus B10S, in the presence of 2,4-DNP, in cultured cells and ammonium daizotrofic conditions. For cells grown in ammonium (RCVNH4) ammonium and more DNP (RCVNH4DNP) gels and 17 cm pH range 5-8, thirteen patches (protein) were detected, which once identified, are expected to provide information on the effect of the consumption of ammonium 2,4-DNP, regulating their transport into the cell, expression of gene (s) of nitroreductase (s), nitroreductase activity and the electron donor (s) nitroreductase (s) .