B21L-03:
Metabolic Ecology of Chemosynthetic Nitrate Respiration at Deep-Sea Vents
Tuesday, 16 December 2014: 8:30 AM
Ileana M. Perez-Rodriguez, Carnegie Inst Washington, Washington, DC, United States, Stefan Manfred Sievert, Woods Hole Oceanographic Inst, Woods Hole, MA, United States, Marilyn L Fogel, University of California Merced, Merced, CA, United States and Dionysios Foustoukos, Carnegie Institute, Washington, DC, United States
Abstract:
Metabolism, the biological processing of energy and matter, is driven by multiple reduction-oxidation reactions under unusually extreme physico-chemical conditions in deep-sea hydrothermal vents. Dissimilatory nitrate reduction to ammonium (DNRA) is one such metabolism that is emerging as widespread in thermophilic members of the e-Proteobacteria and Aquificales, two abundant groups of vent microorganisms. In this study, we used Caminibacter mediatlanticus and Thermovibrio ammonificans as representatives of each group to study physiological and biogeochemical parameters associated with the oxidation of H2 coupled to DNRA. We observed that while C. mediatlanticus achieved higher cell densities than T. ammonificans, the overall metabolism of the latter was ~ 2.8 times higher and ~ 3 times faster. A comparison with previously published data from cultured vent e-Proteobacteria and Aquificales utilizing the same metabolism suggests that the bioenergetics observed in our experiments are generally conserved between these two groups. The discrimination values for the nitrogen isotope (15N/14N) fractionation during DNRA were -6.0 ± 0.7‰ for C. mediatlanticus and -8.4 ± 0.5‰ for T. ammonificans. Further laboratory culturing efforts at seafloor pressures (20MPa) showed that these δ15N discrimination factors were independent of pressure effects, while growth rates and nitrate reduction kinetic rate constants were significantly decreased in both representative microorganisms. Currently, we are complementing these pure culture research approaches with new studies using natural vent microbial communities to further constrain the role of DNRA at in-situ seafloor temperatures and pressures. This study represents the first detailed assessment of the relationship between growth efficiencies and metabolic rates during energy and matter transfer through H2-oxidizing DNRA by members of two mayor phylogenetic groups present at hydrothermal vents. Furthermore, determinations of nitrogen isotope fractionation during this metabolism will allow the evaluation of its contribution to the observed isotope geochemistry of NO3- and NH4+ in deep ocean environments.
