In this work we compare the protein expression patterns of the three strains in response to arsenic by proteomic approach, strains were grown in absence of the metalloid and in presence of As(III) and As(V) sublethal concentrations and the protein separation was carried out in 2D electrophoresis gels (2D-GE). In total, 999 spots were detected, between 77 and 173 of which showed significant changes for As(III) among the three strains, and between 90 and 143 for As(V) respectively compared to the corresponding control condition. Twenty-eight of those were identified by mass spectrometry (MS).