Cloning and gene expression analysis of pollutant-responsive genes in deep sea Bathymodiolin mussels



We propose to develop molecular biomarkers of organic chemical exposure in bathymodiolin deep sea mussels, focusing on Bathymodiolus thermophilus (Bivalvia: Mytilinae) and related species.  Bathymodiolin mussels are deep sea bivalves of the family Mytilidae, found at hydrothermal vents and cold seeps.  Closely related species (Idas spp. and Adipicola spp.) colonize sunken wood and whale carcasses (‘organic falls’).  Due to the technical difficulties of obtaining appropriately preserved deep-sea samples, very little information is available on the gene sequences and gene expression patterns of these important bivalves.  Bathymodiolus spp.  are closely related to the shallow-water Mytilus edulis (blue mussel), for which we have some gene sequences and will be obtaining more.  By leveraging the evolutionary relationships between these mussel species, we propose to obtain gene sequences in Bathymodiolus that could serve as markers of chemical exposure and inform our understanding of the chemical environment of the deep sea vent environment.

The studies will involve cloning and sequencing cytochrome P450 (CYP) genes that are candidates for regulation by organic chemicals to unambiguously establish relationships, and eventually determining their response to chemical exposure experimentally.  We have already begun to approach the full complement of CYP sequences expressed in mussels and oysters, and have been the first to employ quantitative PCR based on confirmed sequences for a defined suite of Mytilus genes.

The approach will include:

- cloning and sequencing selected genes to identify full-length sequences and to confirm that the genes are expressed

- examining gene expression of selected genes in an extant Bathymodiolus sample collection relative to concurrently collected in-situ chemical data

Abiogenic hydrocarbons have been identified at seeps and vents in the deep sea.  Low molecular weight (C1-C4) alkanes serve as carbon sources for microbes, and indirectly also for higher organisms.  In addition, at some locations (e.g in the Gulf of Mexico and elsewhere) there are petroleum seeps.  How animals in those environments deal with these potentially toxic compounds is not known.  Bivalves are known to accumulate hydrocarbons and could have evolved means to oxidize these.  In animals, the enzymes that oxidize hydrocarbons are principally the cytochrome P450 enzymes.  This grant, though small, would enable us to provide critical information to address molecular responses in mussels exposed to organic chemicals and to help define the chemical environment experienced by the biota surrounding deep sea vents and seeps.