Protein Expression in Baltic Sea Blue Mussels Exposed to Natural and Anthropogenic Stress

The focus of this thesis is the early detection of stress in the environment. It has been proposed that studies on the cellular level would detect stress reactions earlier in time compared to common physiological methods. In a series of experiments it was investigated how different stress factors, both natural and introduced by man, affect levels of stress proteins. Oneand two-dimensional gels were used to determine individual proteins and families of proteins. The two-dimensional gels were also used in a proteomic approach, where the presence and absence of proteins after treatment was observed, and the protein expression signatures (PES) were identified. Baltic Mytilus edulis was used in all experiments and it is evident that earlier observed differences in physiological rates and pollution sensitivity, compared to marine mussels, is also manifested as lower concentrations of stress proteins after exposure to copper and cadmium. When the Baltic mussels were allowed to acclimate for one month the difference decreased, suggesting an environmentally induced difference (paper I). Pre-exposure to heat before exposure to either a second heat-shock or cadmium was found to enhance the levels of HSP70 and thus tolerance, significantly (paper II). Exposure to a mixture of stress factors (PCB (Aroclor 1248), copper and lowered salinity) revealed synergistic, additive as well as antagonistic effects in induction of 6 different stress proteins. When analyzing a large number of proteins with two-dimensional gels and the MELANIE II 2D software it was shown that it is possible to identify PES with this technique, and hypothesized that it could be possible to separate responses to mixtures of different stress factors (Papers III and IV). Different techniques were also applied to analyze the protein expression pattern when mussels were exposed to PAHand PCB-fractions extracted from natural Baltic Sea sediments. In this experiment the protein assays were accompanied by physiological measurements. All methods used strongly indicated stressed conditions, and the variation between individual mussels within treatments was smaller in terms of protein response than for physiological parameters (paper V). It is concluded that measuring the induction of stress proteins is a reliable way to detect stressful conditions. Proteins visualized on a one dimensional gel give a “gross” picture of an organism’s condition. The major challenge is to identify the origin and severity of the elucidated stress response. Further mapping of twodimensional gels suggested that protein patterns are specific to type and level of stress. A most important future step is to establish links between sub-cellular protein response to well known physiological effects. This should include long term experiments where altered protein expression signatures are linked to life history characteristics like survival, growth and reproductive success.