AME 49:223-232 (2007)  -  DOI:

Biomass reallocation within freshwater bacterioplankton induced by manipulating phosphorus availability and grazing

Thomas Posch1,*, Birgit Mindl2, Karel Hornák3, Jan Jezbera3, Michaela Maria Salcher1, Birgit Sattler2, Bettina Sonntag2, Jaroslav Vrba3, Karel Šimek3

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
3Biology Centre ASCR, v.v.i., Institute of Hydrobiology and Faculty of Biological Sciences, University of South Bohemia, Na Sádkách 7, 370 05 Ceské Budejovice, Czech Republic

ABSTRACT: Grazing by bacterivorous protists and the availability of nutrients strongly affect the taxonomic composition of freshwater bacterioplankton. However, so far, studies have focussed mainly on changes in abundance. Therefore, we studied biomass reallocation within different phylogenetic lineages of bacteria under varying regimes of protistan grazing and nutrient supply in the oligo-mesotrophic Piburger See (Austria). Size fractionation of lake water was used to create setups with and without bacterivores. These treatments were incubated in bottles (with and without added P) and in dialysis tubes (allowing for free nutrient exchange) for 96 h. The release of bacteria from grazing resulted in a small increase in total abundance, but more pronounced changes of production and biomass. Addition of P to bottles seemed to indicate P limitation of bacterial growth. However, this was contradicted by the results of dialysis tube incubations. In these treatments, highest bacterial biomass and production were observed as well as a substantial increase in particulate P in the bacterial size fraction. While Betaproteobacteria abundance and biomass increased greatly in P-surplus bottles (4× and 12×, respectively), biomass increased even more in the dialysis tubes (28×). After 48 h incubation, virtually all imported P in predator-free dialysis tubes could be attributed to newly produced betaproteobacterial biomass. These bacteria were significantly reduced by the presence of predators in the bottle incubations only, probably due to the delayed growth of bacterivores in the dialysis tubes. By contrast, although Actinobacteria numerically dominated in the lake, as well as in the grazing-exposed bottle treatments, their contribution to total biomass was always low. Our results illustrate that the quantification of the biomass of specific lineages may allow for a better assessment of C and P fluxes within microbial food webs. Moreover, nutrient addition during bottle incubations might result in misleading conclusions about growth limitation.

KEY WORDS: Actinobacteria · Bacterial biomass · Bacteria–flagellate interactions · Bacterial lineages · Betaproteobacteria · Fluorescence in situ hybridization · Phosphorus enrichment

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Cite this article as: Posch T, Mindl B, Hornák K, Jezbera J and others (2007) Biomass reallocation within freshwater bacterioplankton induced by manipulating phosphorus availability and grazing. Aquat Microb Ecol 49:223-232.

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