Cloning and expression of MDR transporters from marine bivalves, and their potential use in biomonitoring.

Multidrug resistance transporters (MDRs) are excellent candidates for molecular-level biomonitoring - they function in exporting xenobiotic compounds and their expression is inducible. However, currently available MDR sequence information from aquatic invertebrates is partial and mostly biased towards the conserved ATPase domain. In the present study, two genes belonging to the MDR/TAP (ABCB) family were cloned and characterized from the bivalve Brachidontes pharaonis, which thrives in rocky environments along the Israeli Mediterranean coast. One of these is a complete sequence of a 'half'ABCB, probably belonging to the ABCB10 subfamily, while the second is a 'full'ABCB1 transporter. A quantitative RT-PCR protocol for biomonitoring was tested in laboratory experiments. Bivalves exposed to diesel showed significant increase in B1 expression levels, while the expression of B10 was suppressed. These results suggest that B. pharaonis features an MDR1 homologue that is induced by pollution and may serve as a sentinel organism for routine biomonitoring programs. However, our findings also exemplify that not all MDRs are equally suitable for this purpose and sequence information must be expanded beyond the ATPase domain for correct classification of cloned genes.