title: Effect of nutrient loading on bacterioplankton community composition in lake mesocosms.
abstract: Changes in bacterioplankton community composition were followed in mesocosms set up in the littoral of Lake Vesijärvi, southern Finland, over two summers. Increasing nitrogen and phosphorus concentrations in the mesocosms represented different trophic states, from mesotrophic to hypertrophic. In 1998, the mesocosms were in a turbid state with a high biomass of phytoplankton, whereas in 1999, macrophytes proliferated and a clear-water state prevailed. The bacterial communities in the mesocosms also developed differently, as shown by denaturing gradient gel electrophoresis profiling of partial 16S rRNA gene fragments and by nonmetric multidimensional scaling analysis. In 1998, nutrient treatments affected the diversity and clustering of bacterial communities strongly, but in 1999, the bacterial communities were less diversified and not clearly affected by treatments. Canonical correspondence analysis indicated that bacterioplankton communities in the mesocosms were influenced by environmental physicochemical variables linked to the increasing level of eutrophication. Nitrogen concentration correlated directly with the bacterioplankton composition. In addition, the high nutrient levels had indirect effects through changes in the biomass and composition of phyto- and zooplankton. Sequencing analysis showed that the dominant bacterial divisions remained the same, but the dominant phylotypes changed during the 2-year period. The occurrence of Verrucomicrobia correlated with more eutrophic conditions, whereas the occurrence of Actinobacteria correlated with less eutrophic conditions.
authors.affiliation: Department of Applied Chemistry and Microbiology, University of Helsinki, P.O. Box 56, Viikki Biocenter, 00014, Helsinki, Finland. kaisa.haukka@ktl.fi
authors.forename: Kaisa
authors.initials: K
authors.lastname: Haukka
authors.forename: Eija
authors.initials: E
authors.lastname: Kolmonen
authors.forename: Rafiqul
authors.initials: R
authors.lastname: Hyder
authors.forename: Jaana
authors.initials: J
authors.lastname: Hietala
authors.forename: Kirsi
authors.initials: K
authors.lastname: Vakkilainen
authors.forename: Timo
authors.initials: T
authors.lastname: Kairesalo
authors.forename: Heikki
authors.initials: H
authors.lastname: Haario
authors.forename: Kaarina
authors.initials: K
authors.lastname: Sivonen
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D017753:Ecosystem; D004591:Electrophoresis, Polyacrylamide Gel; D004784:Environmental Monitoring; D005068:Eutrophication; D005387:Finland; D005618:Fresh Water / Q000032:analysis*; D009584:Nitrogen / Q000032:analysis; D010933:Plankton / Q000302:isolation & purification*; D012329:RNA, Bacterial / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013045:Species Specificity
chemical_list: D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D009584:Nitrogen