Effect of different environmental variables on the synthesis of Hsp70 in Raphidocelis subcapitata

Heat-shock proteins (Hsp) or stress proteins are strong candidates for biomarkers of environmental pollution since they are activated very early in the cascade of cellular events that follow toxic exposure and at concentrations below the lethal dose. Included in a test battery comprised of different bioassays, Hsp induction could provide a general purpose tier I indicator of pollution. Still, little is known on the induction of Hsp under different environmental conditions. In the present study we have made use of an Enzyme Linked Immunosorbent Assay (ELISA) to detect the synthesis of Hsp70 in Raphidocelis subcapitata in response to changes in pH, temperature, humic acids, nitrates and phosphates. The results show that algae respond to these changes in the environment by a transient increase in Hsp70 levels, the extend of which is dependent on the actual parameter under investigation. Out of these five parameters studied, only temperature and possibly pH were able to induce acquired tolerance, i.e. algae grown at a pH or at a temperature different from control conditions were shown to have acquired resistance to a subsequent challenge with Zn (10(-5) M). Adjustment of the pH and temperature in two physico-chemically different natural surface waters was demonstrated to be sufficient to obtain similar induction patterns of Hsp70 upon exposure to zinc. These results qualify Hsp70 as a good biomonitor for environmental pollution provided essential environmental parameters such as pH and temperature are kept constant.