Collaborative Research: Metabolic Rates and Growth Efficiency across Redox and Thermal Gradients: An Experimental Study to Constrain Biomass Production at Vents

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Although they are the base of the food-web in deep sea hydrothermal systems, the growth efficiencies and other essential metabolic characteristics of microorganisms that live off chemical energy from geothermal/mineralogical sources in hydrothermal vent areas in the deep ocean are poorly known. This research uses a novel, flow through, laboratory reactor apparatus to run first-of-a-kind experiments looking at microbial growth rates and metabolic efficiencies at the temperatures, pressures (100 to 250 bars), and chemical conditions found in hydrothermal systems on the deep seafloor. Experiments will target the metabolic processes of two common deep sea vent microorganisms by measuring, in the reactor solutions, nitrogen-bearing respiratory products of nitrate-reducing and hydrogen-oxidizing microbes. Research goals are to determine the role of redox gradients on nitrate reduction and ammonification in hydrothermal systems, use isotopes to determine metabolic rates using kinetic isotope effects, and determine the growth efficiency of mesophilic and thermophilic anaerobic microbes at a range of H2/CO2 molar ratios. Broader impacts of the work include cross-training of a graduate student in two disciplines and laboratories and inclusion of a student from an under-represented minority in research.