Anton Wille

Phylogenetic and functional heterogeneity of sediment biofilms along environmental gradients in a glacial stream.

ABSTRACT We used in situ hybridization with fluorescently labeled rRNA-targeted oligonucleotide probes concurrently with measurements of bacterial carbon production, biomass, and extracellular polymeric substances (EPS) to describe the bacterial community in sediments along a glacial stream. The abundance of sediment-associatedArchaea, as detected with the ARCH915 probe, decreased downstream of the glacier snout, and a major storm increased their relative abundance by a factor of 5.5 to 7.9. Bacteria of theCytophaga-Flavobacterium group were also sixfold to eightfold more abundant in the storm aftermath. Furthermore, elevated numbers of Archaea and members of theCytophaga-Flavobacterium group characterized the phylogenetic composition of the supraglacial ice community. We postulate that glacial meltwaters constitute a possible source of allochthonous bacteria to the stream biofilms. Although stream water temperature increased dramatically from the glacier snout along the stream (3.5 km), sediment chlorophyll a was the best predictor for bacterial carbon production and specific growth rates along the stream. Concomitant with an increase in sediment chlorophylla, the EPS carbohydrate-to-bacterial-cell ratio declined 11- to 15-fold along the stream prior to the storm, which is indicative of a larger biofilm matrix in upstream reaches. We assume that a larger biofilm matrix is required to assure prolonged transient storage and enzymatic processing of allochthonous macromolecules, which are likely the major substrate for microbial heterotrophs. Bacteria of theCytophaga-Flavobacterium cluster, which are well known to degrade complex macromolecules, were most abundant in these stream reaches. Downstream, higher algal biomass continuously supplies heterotrophs with easily available exudates, therefore making a larger matrix unnecessary. As a result, bacterial carbon production and specific growth rates were higher in downstream reaches.

Lake ice microbial communities in alpine and antarctic lakes

The observation that metabolic processes are reduced or completely inhibited at freezing temperatures has influenced microbial ecologists and limnologists, who have commonly concentrated on warm seasons and temperate habitats. High altitude and high latitude sites are not easily accessible and conducting research at low temperatures is not a trivial matter. However, methods for in-situ studies of microbial processes such as bacterial growth and production have been improved to a degree that allows the study of very oligotrophic systems at low temperatures. Furthermore, the construction of observatories and field stations has increased accessibility to high alpine and antarctic ecosystems, which has largely extended our knowledge of microbial life in cold environments.

A conceptual model for niche differentiation of biota within an extreme stream microhabitat

A comprehensive biodiversity study of streams in a 10 km2 glacial catchment (PSENNER et al. 2003) revealed one very distinct but ephemeral microhabitat in the main stream and side channels of the Rotmoosache, Austria (RM). It is characterized by a bloom of the chrysophyte Hydrurus recorded annually for about three months in spring. Although these blooms are a frequent phenomenon in fast flowing high alpine streams (UEHLINGER et al 2002) Hydrurus is common in many other streams at all altitudes in the Alps and other mountain areas (PIPP & ROTT 1994). It is a fast growing species well adapted to cope with nutrient limited conditions (ROTT et al. 2000). Theoretically, Hydrurus in RM might be identified as an r-selected pioneer limited by several resources but favoured by moderate physical disturbance in spring and autumn. Pioneer species likely compete more with other species for resources (TILMAN 1982) than profiting from mutual relationships, but degree of competition and mutualism may differ among associated biota. Although macroinvertebrates related to Hydrurus have been studied from mid-altitudes (MOOG & JANACEK 1991), the structure of the microbial food web, especially in microhabitats of glacial streams above the tree line, is largely unknown. This study is a first attempt to describe the temporal sequences of key biota for a Hydrurus microhabitat observed in a glacial stream.