Chironomus riparius, a non-biting midge (Chironomidae, Diptera), is extensively used in aquatic ecotoxicological studies for assessing acute and sub-lethal toxicities of contaminated sediments and for water monitoring due to their widespread occurrence, short life-cycle, easy to be reared in the laboratory, physiological tolerance to various environmental conditions. To date, the endpoints used for monitoring such effects in C. riparius are based on a small number of specific biomarkers and measurements of organism level effects, such as survival and reproduction. Genomic-based techniques based on expression analysis of genes are important tools for investigating molecular level effects caused by exposure to environmental pollutants, which will provide the ability to detect mechanisms of action and subsequent adverse cellular level effects and associated with different types of toxicity. As a pre-requisite for genomic based ecotoxicological studies knowledge on the C. riparius transcriptome is important but despite its ecotoxicological importance, no large scale transcriptome analysis of C. riparius has been done so far. Therefore, to gain a better understanding of C. riparius transcriptome, we recently developed Expressed Sequence Tags (ESTs) sequencing project on C. riparius larvae using 454 pyrosequencing. Sequencing runs, using normalized cDNA collections from fourth instar larvae, yielded 20,020 expressed sequence tags, which were assembled into 8,565 contigs and 11,455 singletons. Sequence analysis was performed by BlastX search against the National Center for Biotechnology Information (NCBI) nucleotide (nr) and uniprot protein database. Based on the gene ontology classifications, 24% (E-value ≤1-5) of the sequences had known gene functions, 24% had unknown functions and 52% of sequences did not match any known sequences in the existing database. Sequence comparison revealed 81% of the genes have homologous genes among other insects belonging to the order Diptera providing tools for comparative genome analyses. Targeted searches using these annotations identified genes associated with essential metabolic pathways, signaling pathways, detoxification of toxic metabolites and stress response genes of ecotoxicological interest. The results obtained from this study would eventually make ecotoxicogenomics possible in a truly environmentally relevant species, C. riparius. Various C. riparius ecotoxicity studies using stress response genes developed from 454 sequencing will be presented in the conference.

• Jinhee Choi(School of Environmental Engineering, University of Seoul)