Metabolic responses to elevated pCO₂ in the gills of the Pacific Oyster (Magallana gigas) using a GC-TOF-MS-based metabolomics approach

Rising atmospheric carbon dioxide (CO₂), primarily from human fossil fuel combustion and cement production, are resulting in increasing absorption of CO₂ by the oceans, which has led to a decline in ocean pH in a process known as ocean acidification (OA). There is a growing body of evidence demonstrating the potential effect of OA on life-history traits of marine organisms. Consequently, gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) based metabolic profiling approach was applied to examine the metabolic responses of Magallana gigas to elevated pCO₂ levels, under otherwise natural field conditions. CO₂. Oysters were exposed natural environmental pCO₂ (~625.40 μatm) and elevated pCO₂ (~1432.94 μatm) levels for 30 days. Results indicated that 36 differential metabolites with variable importance in the projection (VIP) value greater than 1 and Student's t-test lower than 0.05 were identified. Differential metabolites were mapped in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database to search for the related metabolic pathways. Pathway enrichment analysis indicates that alanine, aspartate and glutamate metabolism and glycine, serine and threonine metabolism were the most statistically enriched pathways. Further analysis suggested that elevated pCO₂ disturb the TCA cycle via succinate accumulation and Magallana gigas most likely adjust their energy metabolic via alanine and GABA accumulation accordingly to cope with elevated pCO₂. These findings provide an understanding of the molecular mechanisms involved in modulating metabolism under elevated pCO₂ levels associated with predicted OA.