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Applied and Environmental Microbiology, June 2003, p. 3036-3047, Vol. 69, No. 6
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.6.3036-3047.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Hans-Peter Grossart,2,
and Helle Ploug3
Danish Institute for Fisheries Research, DK-2920 Charlottenlund, Denmark,1 Institute of Chemistry and Biology of the Marine Environment, University of Oldenburg, D-2611 Oldenburg,2 Max Planck Institute for Marine Microbiology, D-28359 Bremen, Germany3
Received 27 November 2002/ Accepted 28 February 2003
We studied the dynamics of microbial communities attached to model aggregates (4-mm-diameter agar spheres) and the component processes of colonization, detachment, growth, and grazing mortality. Agar spheres incubated in raw seawater were rapidly colonized by bacteria, followed by flagellates and ciliates. Colonization can be described as a diffusion process, and encounter volume rates were estimated at about 0.01 and 0.1 cm3 h-1 for bacteria and flagellates, respectively. After initial colonization, the abundances of flagellates and ciliates remained approximately constant at 103 to 104 and
102 cells sphere-1, respectively, whereas bacterial populations increased at a declining rate to >107 cells sphere-1. Attached microorganisms initially detached at high specific rates of
10-2 min-1, but the bacteria gradually became irreversibly attached to the spheres. Bacterial growth (0 to 2 day-1) was density dependent and declined hyperbolically when cell density exceeded a threshold. Bacterivorous flagellates grazed on the sphere surface at an average saturated rate of 15 bacteria flagellate-1 h-1. At low bacterial densities, the flagellate surface clearance rate was
5 x 10-7 cm2 min-1, but it declined hyperbolically with increasing bacterial density. Using the experimentally estimated process rates and integrating the component processes in a simple model reproduces the main features of the observed microbial population dynamics. Differences between observed and predicted population dynamics suggest, however, that other factors, e.g., antagonistic interactions between bacteria, are of importance in shaping marine snow microbial communities.
Present address: Virginia Institute of Marine Science, Gloucester Point, VA 23062.
Present address: Institute of Freshwater Ecology and Inland Fisheries, 16775 Neuglobsow, Germany.
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