Seasonal Community and Population Dynamics of Pelagic Bacteria and Archaea in a High Mountain Lake

Abstract

The seasonal variations in community structure and cell morphology of pelagic procaryotes from a high mountain lake (Gossenköllesee, Austria) were studied by in situ hybridization with rRNA-targeted fluorescently labeled oligonucleotide probes (FISH) and image-analyzed microscopy. Compositional changes and biomass fluctuations within the assemblage were observed both in summer and beneath the winter ice cover and are discussed in the context of physicochemical and biotic parameters. Proteobacteria of the beta subclass (beta-proteobacteria) formed a dominant fraction of the bacterioplankton (annual mean, 24% of the total counts), whereas alpha-proteobacteria were of similar relative importance only during spring (mean, 11%). Bacteria of theCytophaga-Flavobacterium cluster, although less abundant, constituted the largest fraction of the filamentous morphotypes during most of the year, thus contributing significantly to the total microbial biomass. Successive peaks of threadlike and rod-shaped archaea were observed during autumn thermal mixing and the period of ice cover formation, respectively. A set of oligonucleotide probes targeted to single phylotypes was constructed from 16S rRNA-encoding gene clone sequences. Three distinct populations of uncultivated microbes, affiliated with the alpha- and beta-proteobacteria, were subsequently monitored by FISH. About one-quarter of all of the beta-proteobacteria (range, 6 to 53%) could be assigned to only two phylotypes. The bacterial populations studied were annually recurrent, seasonally variable, and vertically stratified, except during the periods of lake overturn. Their variability clearly exceeded the fluctuations of the total microbial assemblage, suggesting that the apparent stability of total bacterioplankton abundances may mask highly dynamic community fluctuations.

Theory of microbial ecology: Applications in constructing a recirculating aquaculture system

“…This suggests alterations in the structure of the community with variability of the populations exceeding fluctuations in the total microbial community. These findings are in according with results ofPernthaler et al (1998) that observed an apparent stability of the community as a whole appears to mask highly dynamic fluctuations in the populations.The increase in Enterococcus may be explained by it being added to the food as a probiotic and not being incorporated by the tilapia cultivated during the simultaneous cultivation experiment(Del´Duca et al, 2013). In corroboration, we also have the higher density of these bacteria in the tank where the water enters the bioreactor (Mechanical Tank) compared with the last tank in the sequence (Pump Tank).…”

High occurrence of Pacearchaeota and Woesearchaeota (Archaea superphylum DPANN) in the surface waters of oligotrophic high‐altitude lakes

“…Oligotrophic mountain lakes appear as suitable environments for the development of archaeal populations (e.g. Pernthaler et al, 1998;Auguet et al, 2012;Auguet and Casamayor, 2013;Vissers et al, 2013;Hugoni et al 2015), and most of these studies have focused on potential AOA, mainly SAGMCG-1 and MG1. The large lakes data set simultaneously studied here allows us to cover a wide environmental range and to explore the habitat breadth for such poorly explored archaeal groups.…”

Actinorhodopsins: proteorhodopsin‐like gene sequences found predominantly in non‐marine environments

“…Prior to the GOS, no data set had yet revealed the widespread existence of rhodopsins in a freshwater ecosystem . If indeed rhodopsins do originate from actinobacteria in freshwater environments perhaps they are linked to the success of this group previously documented for many rivers and lakes (Pernthaler et al, 1998;Warnecke et al, 2005). While rhodopsins are believed in general to be supplementary energy producers (Bryant and Frigaard, 2006;Gomez-Consarnau et al, 2007), the presence of rhodopsin-encoding genes in dominant members of the microbial community is a trend emerging from both marine and hyperhalophilic ecosystems, where organisms such as P. ubique (Morris et al, 2002) and Haloquadratum walsbyi (Benlloch et al, 2002) dominate.…”