Verrucomicrobia in situ abundance and water chemistry in a humic lake during the year 2000

Members of the highly diverse bacterial phylum Verrucomicrobia are globally distributed in various terrestrial and aquatic habitats. They are key players in soils, but little is known about their role in aquatic systems. Thus, we applied newly designed 16S rRNA-targeted probe set for the identification of Verrucomicrobia and of clades within this phylum to a study concerning the seasonal abundance of Verrucomicrobia in waters of the humic lake Große Fuchskuhle (Germany) by catalyzed reporter deposition fluorescence in situ hybridization. The Lake Große Fuchskuhle is located in the large Mecklenburg-Brandenburg lake district near Berlin (53°10'N, 13°02'E). The lake was artificially divided into four basins (northwest, northeast, southwest, and southeast). We chose the two most contrasting basins, the acidotrophic humic southwestern (SW) basin with a high influx of allochthonous dissolved organic carbon (DOC) and the more mesotrophic northeastern (NE) basin, to study abundance and seasonality of Verrucomicrobia. Lake water was collected from depths of 0.5 m (oxic) and 4.5 m (seasonally anoxic) approximately trimonthly in 2000 (March, June, September and December). The lake hosted diverse Verrucomicrobia clades in all seasons. Either Spartobacteria (up to 19%) or Opitutus spp. (up to 7%) dominated the communities, whereas Prosthecobacter spp. were omnipresent in low numbers (<1%). Verrucomicrobial abundance and community composition varied between the seasons, and between more and less humic basins, but were rather stable in oxic and seasonally anoxic waters.