IR Home
AME
Home
Editors
Forthcoming
Information
Subscribe
Journals
Home
MEPS
AME
CR
DAO
ESEP
ESR
Search
Subscribe
Book Series
EE Books
Top Books
ESEP Books
Order
EEIU Brochures
(pdf format)
Discussion Forums
Home
Research
IR Research
Institutions
International Ecology Institute
Eco-Ethics International Union
Foundation
Otto Kinne Foundation
![](../../../../images/pixel.gif) | ![](../../../../images/pixel.gif) |
AME 35:297-308 (2004)
|
Abstract
|
![](../../../../images/hline.gif)
Exopolymer production and microcolony formation by planktonic freshwater bacteria: defence against protistan grazing
Martin W. Hahn1,3,*, Heinrich Lünsdorf2, Lore Janke1
1Max Planck Institute for Limnology, Department of Physiological Ecology, PO Box 165, 24302 Plön, Germany
2German Research Center for Biotechnology, Division of Microbiology, Mascheroder Weg 1a, 38124 Braunschweig, Germany
3Present address: Institute for Limnology, Austrian Academy of Sciences, Mondseestrasse 9, 5310 Mondsee, Austria
*Email: martin.hahn@oeaw.ac.at
![](../../../../images/hline.gif)
ABSTRACT: The defence mechanisms of 2 novel bacterial isolates against protistan grazing were investigated in experiments with batch and continuous cultures. Strains MWH55 and MWH73 were isolated from the plankton of mesotrophic lakes using culture
conditions with strong flagellate grazing pressure. The analysis of their 16S rRNA genes revealed that both strains belong to the Betaproteobacteria and demonstrated a close phylogenetic relatedness to bacteria previously detected by
culture-independent methods in river biofilms and lake snow aggregates. Both strains showed a very weak sensitivity to flagellate predation, and both formed planktonic microcolonies that exceeded the upper size limit for ingestion by flagellates, and were
thus protected from predation. These microcolonies consisted of cells embedded in a common exopolymeric matrix, yet lacked direct cell-to-cell contact between neighbouring cells. The structure of the exopolymeric matrix of the microcolonies was
visualized by electron microscopy, while detection of exopolysaccharides by several fluorescently labeled lectins failed. The matrix possessed a complex 3-dimensional structure with strain-specific characteristics. Currently, it is not clear whether the 2
isolates possess a planktonic life strategy or whether they switch between sessile (biofilm or lake snow aggregates) and planktonic dispersal stages. In both cases, however, a low sensitivity of the planktonic stages to protistan predation is
ecologically advantageous. The ability to form an exopolymeric matrix enabling the formation of predation-protected microcolonies is assumed to play a key role in the ecology of these bacteria.
KEY WORDS: Exopolymers · Bacteria · Predation protection · Flagellate grazing · Microcolony formation · Lectins
Full text in pdf format
![](../../../../images/hline.gif)
Published in AME Vol.
35, No. 3
(2004) on May 19
Print ISSN: 0948-3055; Online ISSN: 1616-1564.
Copyright © Inter-Research, Oldendorf/Luhe, 2004
|