Imaging eubacteria and archaean cell abundance and nitrification activity on marine snow particles collected from the South Pacific using microscopy and nanoSIMS

Rachel Foster1, Alyson E Santoro2, Daniela Tienken3, Sten Littman3, William Berelson4 and Marcel Martinus Maria Kuypers5, (1)Stockholm University, Department of Ecology, Environment and Plant Sciences, Stockholm, Sweden, (2)University of Maryland Center for Environmental Science Appalachian Laboratory, Frostburg, MD, United States, (3)Max Planck Institute for Marine Microbiology, Biogeochemistry, Bremen, Germany, (4)University of Southern California, Department of Earth Sciences, Los Angeles, CA, United States, (5)Max Planck Institute for Marine Microbiology, Department of Biogeochemistry, Bremen, Germany
Abstract:
The abundance and nitrification activity by marine-snow associated eubacteria and archaea were measured on particles collected in the South Pacific. The particles were first collected from 24 hour floating sediment traps moored at 100 and 200 m and later amended and incubated with 13C-bicarbonate and 15NH4 for 48 hours. Enrichment for 13C and 15N in cells above natural abundance was quantified using a coupled halogenated in situ hybridization assay with nano-meter scale secondary ion mass spectrometry (HISH-SIMS). Approximately 82% ± 10 of the observed hybridized cells were Eubacterial, while 24% ± 5 were positively hybridized with the Archaean probe. There was high variability in 13C/12C and 15N/14N in both bacterial and archaeal cells. Complementary measurements of δ15NNO3 at the conclusion of the experiment indicated no detectible nitrification activity associated with the particles. Thin sections of the particles imaged with Transmission Electron Microscopy (TEM) showed that a higher abundance of degrading phytoplanktonic cells, including numerous empty radiolarian and diatom frustules were associated with the deeper moored tap, while the shallow trap collected intact bacterial cells, including small picocyanobacteria. Single cell imaging and observations such as those presented here can provide subtle insights and measurements of cellular activity that are often diluted by bulk approaches and that are directly applicable to modeling N and C cycling.