Gene expression analysis for a systems-understanding of contaminated environments

Ecotoxicological assessment is mainly focused on chemicals and compounds displaying similar effects. As a useful outcome of this approach, yet, a standard battery of robust and cost effective biotests is available. The challenge, however, is the differentiation between multiple effects caused by complex contaminant mixtures and the unspecific toxicity endpoints such as survival, growth or reproduction. Moreover, the molecular mechanisms beyond these endpoints are numerous, and the mode of actions can be both synergistic and antagonistic, sometimes even resulting in a compensatory way.

With respect to ecotoxicology, it is important to understand the mode of actions of various pollutants on organisms for the development of predictive simulation models and for the correlation of molecular biomarkers with population-level effects. Powerful techniques like DNA-microarrays were developed that allow the analysis of the transcriptome of a cell or an organism. This technique provides comprehensive information about the cellular status that is a result of its genetic equipment, adaption to the environment, and actual stress by environmental factors. Due to the plasticity of the transcriptome it is a sensitive indicator for changes in environmental conditions like temperature, nutrition, but also stress induction, including exposure to toxicants.

In several study we exposed the nematode Caenorhabditis elegans to single substances (both on agar, liquid medium or soil cultures) as well as sediments of German rivers with varying (low, medium and high) levels of heavy metal and/or organic contaminations. Our experiments demonstrated how ecotoxicogenomics can identify transcriptional responses in both individual loading scenarios and complex mixtures helping to identify underlying modes of actions.