2D-electrophoretic analysis for studying the tolerance to heavy metals in Rhodobacter sphaeroides

The influence of metal ions on the photosynthetic growth of the facultative anaerobic bacterium Rhodobacter sphaeroides strain R-26.1 is presented. The ability of this bacterial strain to grow photosynthetically in highly contaminated environments was tested in liquid anaerobic media containing transition metal cations Hg2+, Cu2+, Fe2+, Ni2+, Co2+ and oxyanions, such as MoO42- and CrO42-. Growth analysis of Rhodobacter sphaeroides incubated with cobalt and chromate shows a light reduction of growth ability but a relevant cobalt and chromate bioaccumulation [1].This relationship is fundamental in bioremediation of heavy metal polluted sites. The tolerance towards Co2+ of this bacterial species appears particularly high compared to that of other micro-organisms. Preliminary data suggest a role of small soluble proteins in the resistance mechanism to Co2+ exposure.To elucidate the effect of Co2+ on the enzymes involved in tolerance response, a proteomic approach was chosen. Using bidimensional electrophoresis, maps of soluble proteins from R. Sphaeroides R-26.1, grown with and without Co2+ (5mM), have been produced. Many differences can be identified between R. sphaeroides proteomes from control cells and from cells incubated with 5mM Co2+. We have chosen as significative all the spots having a t-Student value ranging between 5 and 19. In this range 53 spots has been identified which will be further analysed by peptide mass fingerprinting.