Award: OCE-1356010

Throughout the oceans, the diverse pool of organic molecules dissolved in seawater represents one of the largest stores of reduced carbon on Earth. Because it is comparable in size to the atmospheric CO2 reservoir, knowing the factors that control the fate of this carbon store (referred to as DOM, for 'dissolved organic matter') is critical for understanding the global carbon cycle. It is a surprisingly difficult task to gain this understanding, mainly because of the vast number of compounds that make up marine DOM (current estimates suggest there are tens of thousands of different compounds in just a handful of seawater) and because of the equally vast number of bacterial species that selectively choose compounds from marine DOM to use as nutrition. Our project simultaneously examined the chemical changes and the bacterial activities that modify marine DOM, which we accomplished by assembling a team of chemists and microbiologists to collect data, and data analysis specialists to assemble and integrate the resulting information. Our work focused on southeastern U.S. coastal waters, with our research base located at the University of Georgia Marine Institute on Sapelo Island. We collected seawater samples that covered different seasons, tidal regimes, and weather conditions. For the chemical analyses, a recently developed method called Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS, for short) was used. This allowed us to determine the formula of the compounds in the DOM, and examine how they changed over time as marine bacteria selectively removed molecules. In this coastal ocean ecosystem, we found evidence for >10,000 unique compounds. For the microbiological component, we examined messenger RNA in bacterial cells. This technique (known as metatranscriptomics) provides information on the genes being used by the bacterial community to selectively change the DOM pool. Results of our research indicated that some molecules were rapidly removed from the DOM pool, almost as quickly as they were released. These included compounds characterized as osmolytes, carboxylic acids, fatty acids, sugars, and organic sulfur compounds. In the case of larger molecules, marine bacteria remove the parts that are more easily used for nutrition. Compounds of marine origin were preferred over those coming from terrestrial sources such as rivers and marshes. Compounds containing sulfur and nitrogen were also preferred over those that didn?t. Together, these data provide new information on how marine bacteria cycle the molecules dissolved in seawater and affect carbon fluxes on a global scale. We partnered with a local high school science teacher to provide opportunities for her class to apply molecular biology techniques in the study of marine bacteria, both in the classroom and at Sapelo Island. These acrivities contributed to the studetns' Advanced Placement biology curriculum requirements. Last Modified: 04/05/2018 Submitted by: Mary Ann Moran