JPR Advance Access originally published online on November 22, 2005
Journal of Plankton Research 2005 27(12):1261-1272; doi:10.1093/plankt/fbi092
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Effect of nutrient enrichment on bacterioplankton biomass and community composition in mesocosms in the Archipelago Sea, northern Baltic

1 Section of Ecology, Department of Biology, University of Turku, FIN-20014 Turku, Finland, 2 Department of Applied Chemistry and Microbiology, Viikki Biocenter, PO Box 56, FIN-00014 University of Helsinki, Finland and 3 SW Finland Regional Environment Centre, PO Box 47, FIN-20801 Turku, Finland
Present Address: National Public Health Institute, Mannerheimintie 166, 00300 Helsinki, Finland
* Corresponding Author: kaarina.sivonen{at}helsinki.fi
Received July 21, 2005; accepted in principle August 25, 2005; accepted for publication October 27, 2005; published online November 22, 2005
Communicating editor: K.J. Flynn
Effects of nutrient enrichment on the biomass and community composition of heterotrophic bacteria and picocyanobacteria were studied in large (42 m3) mesocosms in the brackish-water Archipelago Sea (Baltic Sea) in late summer 2000 using cell counts and denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 16S rRNA gene fragments. The identity of the major DNA bands was determined by sequencing. The obtained sequences were related to
- and
-proteobacteria, actinobacteria, verrucomicrobia and cyanobacteria. Nitrogen and phosphorus additions increased the biomasses of heterotrophic bacteria and picocyanobacteria and caused significant changes in their community composition judging from the DGGE banding patterns. Most verrucomicrobial bands had their highest relative intensity in the control treatment and their lowest in the higher nutrient addition treatment, whereas most Synechococcus-related bands had their lowest relative intensity in the lower nutrient addition treatment. The responses of proteobacteria and actinobacteria were more variable. The presence of both freshwater and marine sequences among the closest relatives to our sequences highlights the intermediate character of the Archipelago Sea between a freshwater and truly marine environment.