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.

Response of heterotrophic stream biofilm ­communities to a gradient of resources

“…Numerous studies have shown that enrichment alters the general community structure of bacterial biofilm and planktonic communities , Schäfer et al 2001, Chenier et al 2003, Haukka et al 2006), but resolution has been limited. Declines in the richness of bacterioplankton (Carlson et al 2002, Bertoni et al 2008, or in their evenness (Sipura et al 2005), with enrichment have been observed in some planktonic studies, supporting the trend observed in the present study.…”

A Guide to the Natural History of Freshwater Lake Bacteria

“…Actinobacteria taxa have not been found in physical association with members of the Cyanobacteria or other phytoplankton (116) but may become a greater part of the bacterioplankton community during phytoplankton blooms (3,174,237). Generally, increased nutrient concentrations select against the freshwater lake Actinobacteria (90). This disadvantage does not seemingly stem from an inability to assimilate common substrates, as the Actinobacteria have been shown to be capable of incorporating arginine, leucine, and thymidine at rates similar to those of other common freshwater lake taxa (23) or as the most active bacterial fraction for amino acid uptake (174).…”

Seasonal and Spatial Changes of Planktonic Bacterial Communities Inhabiting the Natural Thermal Lake Hévíz, Hungary

“…At that time representatives of 10 phyla (Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes, Cyanobacteria, Chlorobi, Chlorofl exi, Deferribacteres, Nitrospirae, Spirochaetes and Verrucomicrobia) were identifi ed by cloning and 4 phyla (Firmicutes, Actinobacteria, Proteobacteria and Bacteroidetes) by cultivation, nevertheless the overlap between the sediment and planktonic bacterial community compositions were negligible regarding the lower taxonomic (e.g. genus) levels [29]. Other microbial investigations on aquatic environments also confi rmed that bacterial communities associated with surfaces clearly differed from free-living communities [30,31].…”