Vertical and longitudinal distribution patterns of different bacterioplankton populations in a canyon-shaped, deep prealpine lake

The pelagic zone of large, deep freshwater lakes features pronounced horizontal and vertical gradients of physicochemical parameters, which in turn might allow for a nonuniform occurrence of specifically adapted bacterial taxa. We, therefore, studied the spatial distribution patterns of different heterotrophic bacteria, picocyanobacteria, and the dominant primary producer, the filamentous cyanobacterium Planktothrix rubescens, in a large, canyon-shaped, prealpine lake (Lake Zurich, Switzerland), in six vertical profiles along a 21.7-km longitudinal transect. Highest total densities and proportions of cells with high nucleic acid content were in the warm epilimnion and the hypoxic zone of the hypolimnion. P. rubescens formed a dense layer in the metalimnion throughout the lake, whereas picocyanobacteria populated the water layers above. The epilimnion was mainly inhabited by ultramicrobacteria related to the LD12-lineage of Alphaproteobacteria and to Actinobacteria; the latter group preferred the shallow regions. Cytophaga-Flavobacteria, in particular a population related to Fluviicola sp. were more frequent in and below the layer of maximal P. rubescens abundances. Betaproteobacteria, on the other hand, were highly abundant in the epiand hypolimnion, but not in the P. rubescens layer. Four betaproteobacterial subpopulations with contrasting longitudinal and/or vertical habitat preferences were distinguished: putatively methylotrophic bacteria of the LD28 lineage (beta IV) preferentially inhabited the hypolimnion, Polynucleobacter acidiphobus was found throughout the epilimnion, Limnohabitans (R-BT065) more in the shallow regions of the lake, and Polynucleobacter necessarius ssp. asymbioticus only in hypoxic waters. Our results stress the potential importance of spatial niche differentiation in freshwater bacterioplankton. DOI: https://doi.org/10.4319/lo.2011.56.6.2027 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-133839 Published Version Originally published at: Salcher, Michaela M; Pernthaler, Jakob; Frater, Nakita; Posch, Thomas (2011). Vertical and longitudinal distribution patterns of different bacterioplankton populations in a canyon-shaped, deep prealpine lake. Limnology and Oceanography, 56(6):2027-2039. DOI: https://doi.org/10.4319/lo.2011.56.6.2027 Vertical and longitudinal distribution patterns of different bacterioplankton populations in a canyon-shaped, deep prealpine lake Michaela M. Salcher,* Jakob Pernthaler, Nakita Frater, and Thomas Posch Limnological Station, Institute of Plant Biology, University of Zurich, Kilchberg, Switzerland