Omics Studies On The Physiological Responses Of Pacific Oyster Crassostrea Gigas To CO₂-driven Ocean Acidification

The gradually increased atmospheric CO2 partial pressure(p CO2) has thrown the carbonate chemistry off balance and resulted in decreased seawater p H in marine ecosystem, termed ocean acidification(OA). Anthropogenic OA is postulated to affect the physiological processes of many marine calcifying organisms, such as growth, development and calcification. Marine organisms were also found to respond to hypoxia with varied behavioral, physiological, and cellular responses. Despite the common co-occurrence of hypoxia and acidification in marine systems, their concurrent effects on ocean life are poorly understood. In this work, metabolomics, proteomics and traditionally physiological approaches were integrated to elucidate the effects of seawater acidification and/or hypoxia on Pacific oyster Crassostrea gigas, hopefully shedding light on the effects and mechanisms in a holistic and systematic mode. 1. Proteomic and metabolomic responses of Pacific oyster C. gigas to elevatedp CO2 exposureNMR-based metabolomics and 2-DE-based proteomics were integrated to analyze the perturbance of elevated p CO2 in gills, hepatopancreas and mantles of C. gigas. It was found that seawater acidification could affect several physiological processes in C. gigas such as energy metabolism, osmotic stress and cytoskeleton structure. In gills, the alterations of proteins involved in ectoine biosynthesis, taurine metabolism, citrate cycle and glycerophospholipid metabolism were observed in response to elevated p CO2. In the tissue of hepatopancreas, the processes of protein degradation, galactose metabolism, taurine metabolism, cysteine metabolism and citrate cycle were altered. The alterations of citrate cycle and cytoskeleton structure were observed in mantle tissues. 2. Physiological responses of Pacific oyster C. gigas to elevated p CO2 and hypoxia exposure2-DE-based proteomics and traditionally physiological approaches were applied to elucidate the perturbance of elevated p CO2 and/or hypoxia in C. gigas. Compared with the control group, hypoxia had a severely harmful effect on immune responses of C. gigas. In elevated p CO2 exposure treatment, the variation in abundances of proteins related to oxidative stress, signal transduction and Ca2+ homeostasis were identified. However, the alterations of proteins involved in stress response, signal transduction and cytoskeleton structure were observed under hypoxia exposure. When oysters were exposed to elevated p CO2 associated with hypoxia, proteins significantly altered in abundance were found to participate in the processes of energy metabolism, stress response, Ca2+ homeostasis and protein metabolism.Phosphoproteomic analysis was applied to elucidate the perturbance of elevated p CO2 and/or hypoxia in the mantle of C. gigas. The alterations of proteins involved in energy metabolism(AMP deaminase 2), immune response(Cap1 and Pcdc4), signal transduction(Cdc42), ribosomes(EG664969, Rps14 and Rpsa) and cytoskeleton(Pls3, Cap1 and Cenpj) were observed in mantle of oysters under elevated p CO2 and/or hypoxia exposure. Elevated p CO2 could affect a variety of biological processes, such as MAPK signal transduction and adherens junction. There were several signal transductors(such as Fc epsilon RI signal transduction and T cell receptor signal transduction) arousing in response to hypoxia, which perhaps led to changes in immune responses and regulation of phosphorylation. Elevated p CO2 associated with hypoxia exposure probably influenced the nervous system(Ras signal transduction, Gn RH signal transduction, dopamine and GABAergic synthesis), which resulted in abnormal mantle tissue function.