Award: EF-1416785

Since the beginning of the Industrial Revolution, humans have produced approximately 1,500 billion tons of carbon dioxide through the combustion of fossil fuels. Of that, about 26% is absorbed by the oceans. Carbon dioxide reacts with water to form carbonic acid. The absorption of the gas by the oceans will inevitably lead to a reduction in pH. This phenomenon, called ocean acidification, has the potential to interfere with biological processes, especially the formation of carbonate biominerals that form coral skeletons. Our research is focused on how corals make their skeletons. In the last 5 years, we have worked at various levels on the marine stone building corals, Stylophora pistillata and Montipora capitata. We knew very little about the skeleton forming process and how it might be affected by changes in pH. We compared 20 coral genomes and transcriptomes to identify genes responsible for the formation of coral skeletons. This process also revealed a network of environmental sensors that coordinate responses of the host animals to temperature, light, and pH. Additionally, we identified a variety of stress-related pathways that allow the host animals to detoxify reactive oxygen (ROS) and nitrogen species that are generated by their intracellular photosynthetic symbionts, and determine the survival outcome of corals under environmental stress. The genome information has been extremely useful to the study of this process. Identification of genes responsible for making aragonite based on bioinformatics methods motivated us to express these proteins in bacteria and test if they have the ability to precipitate calcium carbonate solely on their own. As predicted from amino acid compositions, the isolated individual proteins could precipitate calcium carbonates in unamended seawater. Thus, we found that the process of biomineral formation in corals is protein-driven. With biochemical and biophysical methods, we provided evidence for the close association of proteins to the mineral in the aragonitic skeleton (Fig.1). We then used analytical methods (proteomics) to identify and sequence the composite of proteins in these skeletons. Simultaneously, to understand the biomineralization mechanisms, we looked at the expression of genes for the proteins identified by proteomics and that we tested during the development of a coral polyp. Overall, our work revealed that corals have the ability to form skeletons even at pH levels predicted by the end of this century. Our findings suggest once the coral larva or polyp attaches itself to a substrate, aragonite forming genes are expressed, and eventually the proteins responsible for making aragonite are secreted over time. These proteins are temporally and spatially organized in a pattern that is genetically induced. Additionally, our findings suggest that once these proteins are secreted, some of the proteins which are aspartate and glutamate-rich have the ability to nucleate calcium carbonate, which initially forms amorphous calcium carbonate. With the aid of other proteins secreted during the calcification process, a matrix is deposited on which more highly-organized aragonite crystals are deposited. These proteins are thus responsible for the species-specific defined patterns of the coral skeleton. In the end, our research suggests that small changes in oceanic pH will not affect the actual process of making new coral skeleton. Last Modified: 12/19/2018 Submitted by: Paul G Falkowski