Combinatory effects of temperature stress and nonionic organic pollutants on stress protein (hsp70) gene expression in the freshwater sponge Ephydatia fluviatilis

This is the first documentation of a heat shock protein (hsp) response in sponges. Subjecting the freshwater sponge Ephydatia fluviatilis to temperature stress (18° to 33°C; 2 h) resulted in an increased expression (>10 times) of the Mr 70,000 (hsp70). The induction of hsp70 could be demonstrated on the level of gene expression and by quantification of the hsp70 protein. Temperature stress also resulted in a 25% reduction of sponge cell proliferation. A mixture of nonionic organic compounds was extracted from water from the polluted Schwarzbach River (S. Hesse, Germany) by adsorption onto XAD‐7 resin. Concentrations of this Schwarzbach River water extract at two and four times ambient levels resulted in decreases in cell proliferation by 53.6 and 99.4%, respectively. However, when cells were exposed to these levels of the Schwarzbach River water extract directly following a temperature stress (33°C for 2 h), cell proliferation was less affected by the extract than the absence of the temperature stress. In addition, the combination of temperature stress and exposure to the Schwarzbach River water extract resulted in higher levels of hsp70 than were observed for each stressor by itself. Northern and Western blotting as well as precipitation assays confirmed the interaction between heat treatment and exposure to different amounts of nonionic organic pollutants on the level of mRNA and protein expression of hsp70. From these data we conclude that a sublethal treatment of sponges with heat results in a higher tolerance of the animals to chemical stressors. These results are relevant to the real‐world situation where organisms are often exposed simultaneously to a variety of stressors, in contrast to many laboratory exposures that aim to elucidate the effects of individual stressors.