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Applied and Environmental Microbiology, September 2009, p. 5952-5962, Vol. 75, No. 18
0099-2240/09/$08.00+0     doi:10.1128/AEM.00186-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Structure and Composition of Aggregates in Two Large European Rivers, Based on Confocal Laser Scanning Microscopy and Image and Statistical Analyses{triangledown} ,{ddagger}

Birgit Luef,1,{dagger} Thomas R. Neu,2 Irene Zweimüller,1 and Peter Peduzzi1*

Department of Freshwater Ecology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria,1 Helmholtz Centre for Environmental Research—UFZ, Department of River Ecology, Brückstrasse 3A, 39114 Magdeburg, Germany2

Received 26 January 2009/ Accepted 17 July 2009

Floating riverine aggregates are composed of a complex mixture of inorganic and organic components from their respective aquatic habitats. Their architecture and integrity are supplemented by the presence of extracellular polymeric substances of microbial origin. They are also a habitat for virus-like particles, bacteria, archaea, fungi, algae, and protozoa. In this study we present different confocal laser scanning microscopy strategies to examine aggregates collected from the Danube and Elbe Rivers. In order to collect multiple types of information, various approaches were necessary. Small aggregates were examined directly. To analyze large and dense aggregates, limitations of the technique were overcome by cryo-sectioning and poststaining of the samples. The staining procedure included positive staining (specific glycoconjugates and cellular nucleic acid signals) as well as negative staining (aggregate volume) and multichannel recording. Data sets of cellular nucleic acid signals (CNAS) and the structure of aggregates were visualized and quantified using digital image analysis. The Danube and Elbe Rivers differed in their aggregate composition and in the relative contribution of specific glycoconjugate and CNAS volume to the aggregate volume; these contributions also changed over time. We report different spatial patterns of CNAS inside riverine aggregates, depending on aggregate size and season. The spatial structure of CNAS inside riverine aggregates was more complex in the Elbe River than in the Danube River. Based on our samples, we discuss the strengths and challenges involved in scanning and quantifying riverine aggregates.

* Corresponding author. Mailing address: University of Vienna, Department of Freshwater Ecology, Althanstrasse 14, 1090 Vienna, Austria. Phone: 43 1 4277 543 42. Fax: 43 1 4277 9572. E-mail: peter.peduzzi{at}univie.ac.at

{triangledown} Published ahead of print on 24 July 2009.

{ddagger} The authors have paid a fee to allow immediate free access to this article.

{dagger} Present address: Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.

Applied and Environmental Microbiology, September 2009, p. 5952-5962, Vol. 75, No. 18
0099-2240/09/$08.00+0     doi:10.1128/AEM.00186-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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