1. Department of Biological Sciences, University of Calgary, 2500 University Dr. NW, Calgary, Alberta, T2N 1N4, Canada
2. Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, The Netherlands
3. Max-Planck-Institute for Terrestrial Microbiology, Karl-von-Frisch-Straße, D-35043 Marburg, Germany