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Applied and Environmental Microbiology, May 2005, p. 2381-2390, Vol. 71, No. 5
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.5.2381-2390.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Influence of Top-Down and Bottom-Up Manipulations on the R-BT065 Subcluster of ß-Proteobacteria, an Abundant Group in Bacterioplankton of a Freshwater Reservoir

Karel Simek,1,2* Karel Hornák,1,2 Jan Jezbera,1,2 Michal Masín,1 Jirí Nedoma,1 Josep M. Gasol,3 and Michael Schauer4

Hydrobiological Institute of the Academy of Sciences of the Czech Republic, Na sádkách 7, CZ-37005 Ceské Budejovice, Czech Republic,1 Faculty of Biological Sciences, University of South Bohemia, CZ-37005 Ceské Budejovice, Czech Republic,2 Institut de Ciències del Mar-CMIMA, CSIC, Pg. Marítim de la Barceloneta, 37-49, E-08003 Barcelona, Spain,3 Institute for Limnology of the Austrian Academy of Sciences, A-5310 Mondsee, Austria4

Received 23 June 2004/ Accepted 24 November 2004

We studied the effects of nutrient availability and protistan grazing on bacterial dynamics and community composition (BCC) in different parts of the canyon-shaped Rímov reservoir (Czech Republic). The effects of protistan grazing on BCC were examined using a size fractionation approach. Water from the dam area with only bacteria (<0.8 µm), bacteria and heterotrophic nanoflagellates (<5 µm), or whole water were incubated in situ inside dialysis bags. Top-down or predator manipulations (size fractionation) were also combined with bottom-up or resource manipulations, i.e., transplantation of samples to the middle and upper inflow parts of the reservoir with increased phosphorus availability. Significant genotypic shifts in BCC occurred with transplantation as indicated by denaturing gradient gel electrophoresis. Using different probes for fluorescence in situ hybridization, we found that 10 to 50% of total bacteria were members of the phylogenetically small cluster of ß-proteobacteria (targeted with the probe R-BT065). These rod-shaped cells of very uniform size were vulnerable to predation but very fast growing and responded markedly to the different experimental manipulations. In all the grazer-free treatments, the members of the R-BT065 cluster showed the highest net growth rates of all studied bacterial groups. Moreover, their relative abundance was highly correlated with bacterial bulk parameters and proportions of bacteria with high nucleic acid (HNA) content. In contrast, increasing protistan bacterivory yielded lower proportions of R-BT065-positive and HNA bacteria substituted by increasing proportions of the class Actinobacteria, which profited from the enhanced protistan bacterivory.

* Corresponding author. Mailing address: Hydrobiological Institute AS CR, Na sádkách 7, CZ-37005 Ceské Budejovice, Czech Republic. Phone: 420 38 7775873. Fax: 420 38 5310248. E-mail: ksimek{at}hbu.cas.cz.

Applied and Environmental Microbiology, May 2005, p. 2381-2390, Vol. 71, No. 5
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.5.2381-2390.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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