AME 54:113-126 (2009)  -  DOI:

New image analysis tool to study biomass and morphotypes of three major bacterioplankton groups in an alpine lake

Thomas Posch1,*, Josef Franzoi2, Martin Prader2, Michaela Maria Salcher1

1Department of Limnology, Institute of Plant Biology, University of Zürich, Seestrasse 187, 8802 Kilchberg, Switzerland
2Institute of Ecology, University of Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria

ABSTRACT: We present an image analysis routine to determine the contribution of distinct morphotypes to the total abundance and biomass (carbon) of freshwater bacterioplankton and to the fraction of cells detected by fluorescence in situ hybridization via catalyzed reporter deposition (CARD-FISH). The method was tested on bacterial assemblages from an alpine lake (Piburger See, Austria) at characteristic time points during the limnological year. Although on average 51% of 4’,6’-diamidino-2-phenylindole (DAPI)-stained objects were hybridized with the oligonucleotide probe EUB I-III, we detected on average 80% of total biomass determined from DAPI staining. The assemblage was numerically dominated by cocci and rods <0.6 µm (mean cell volume = 0.024 µm3). Only a minor part of these morphotypes could be hybridized (18 and 50%, respectively). In contrast, larger rods (0.087 µm3), cocci (0.155 µm3) and vibrio-shaped cells (0.073 µm3) showed much higher probabilities to be detected by CARD-FISH. These morphotypes per se formed the highest contribution to total biomass, which explained the high detection efficiency of biomass with CARD-FISH. In addition, we determined the seasonal dynamics of morphotype distributions within 3 distinct phylogenetic lineages. Actinobacteria were predominately small rods and cocci, whereas bacteria from the CytophagaFlavobacterium–Bacteroides group formed mainly large rods, cocci and filaments. Betaproteobacteria showed the highest morphological variability. Within all lineages, distinct spatio-temporal dynamics of dominant morphotypes were observed. Thus, the approach presented here will allow for more detailed studies of the amount of carbon bound by different bacterial taxa. This is of relevance as distinct lineages can contribute much more to total bacterial biomass than to total bacterioplankton abundance.

KEY WORDS: Bacterial biomass · Bacterial morphotype · CARD-FISH · DAPI · Image analysis

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Cite this article as: Posch T, Franzoi J, Prader M, Salcher MM (2009) New image analysis tool to study biomass and morphotypes of three major bacterioplankton groups in an alpine lake. Aquat Microb Ecol 54:113-126.

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