Key metabolic pathways involved in xenobiotic biotransformation and stress responses confirmed as revealed by the mangrove oyster Crassostrea brasiliana transcriptome. Crassostrea brasiliana

The Brazilian oyster Crassostrea brasiliana was challenged to three common environmental contaminants: phenanthrene, diesel fuel water-accommodated fraction (WAF) and domestic sewage. Total RNA was extracted from the gill and digestive gland to produce cDNA Libraries which were sequenced using the 454 FLX platform. The transcriptome was assembled using the pool of sequencing data from all cDNA libraries and the resulting circa 20,000 contigs were annotated to produce the first de novo transcriptome for the mangrove oyster C. brasiliana. Sequences were screened to identify genes potentially involved in the biotransformation of xenobiotics and associated antioxidant defence mechanisms. These gene families included those of the cytochrome P450 (CYP450), 70kDa heat shock, antioxidants, such as glutathione S-transferase, superoxide dismutase, catalase and also multi-drug resistance proteins. Analysis showed that the massive expansion of the CYP450 and HSP70 family identified in the Crassostrea gigas genome also occurred in this species, putting the gene duplication events which caused these at the base of the Crassostrea lineage. Preliminary expression analyses were performed which revealed several candidates showing unique up-regulation in each of the three treatments, thus targetting them as potential biomarkers for environmental monitoring.