Showing papers by "Roland Psenner published in 1998"

Determination of Bacterial Cell Dry Mass by Transmission Electron Microscopy and Densitometric Image Analysis

Abstract: We applied transmission electron microscopy and densitometric image analysis to measure the cell volume (V) and dry weight (DW) of single bacterial cells. The system was applied to measure the DW of Escherichia coli DSM 613 at different growth phases and of natural bacterial assemblages of two lakes, Piburger See and Gossenkollesee. We found a functional allometric relationship between DW (in femtograms) and V (in cubic micrometers) of bacteria (DW = 435.V0.86); i.e., smaller bacteria had a higher ratio of DW to V than larger cells. The measured DW of E. coli cells ranged from 83 to 1,172 fg, and V ranged from 0.1 to 3.5 micron 3 (n = 678). Bacterial cells from Piburger See and Gossenkollesee (n = 465) had DWs from 3 fg (V = 0.003 micron 3) to 1,177 fg (V = 3.5 microns3). Between 40 and 50% of the cells had a DW of less than 20 fg. By assuming that carbon comprises 50% of the DW, the ratio of carbon content to V of individual cells varied from 466 fg of C micron-3 for Vs of 0.001 to 0.01 micron3 to 397 fg of C micron3 (0.01 to 0.1 micron3) and 288 fg of C micron3 (0.1 to 1 micron 3). Exponentially growing and stationary cells of E. coli DSM 613 showed conversion factors of 254 fg of C micron-3 (0.1 to 1 micron3) and 211 fg of C micron-3 (1 to 4 micron3), respectively. Our data suggest that bacterial biomass in aquatic environments is higher and more variable than previously assumed from volume-based measurements.

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 (Gossenkollesee, Austria) were studied by in situ hybridization with rRNA-targeted fluorescent- ly 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 the Cytophaga-Flavobacterium cluster, although less abundant, constituted the largest fraction of the filamen- tous 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 mi- crobes, 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 dur- ing the periods of lake overturn. Their variability clearly exceeded the fluctuations of the total microbial as- semblage, suggesting that the apparent stability of total bacterioplankton abundances may mask highly dy- namic community fluctuations.

Climate change as the primary cause for pH shifts in a high alpine lake

Abstract: Chemical and biological sedimentary records of a high alpine lake were used to reconstruct palaeoecological conditions and compared with two centuries of instrumental temperature measurements. Air temperature determined the lake water pH throughout the past 200 yr almost regardless of the level of atmospheric deposition. Our data suggest a strong climate forcing of the acid-base balance in sensitive high-altitude lakes. Their physico-chemical conditions and biota strongly depend on the duration of ice and snow cover which is significantly different between warm and cold periods. Beside changes in weathering rates, in-lake alkalinity generation and water-retention time, delayed freezing in autumn and earlier ice-out dates with a shorter duration of CO2 over-saturation could be crucial for the tight temperature-pH coupling.

Life at the freezing point.

Abstract: Microbial communities are known to exist in extremely hot environments such as hydrothermal vents, but what about extremely cold regions? In their Research Commentary, Psenner and Sattler discuss results reported in the same issue by Priscu et al. in which a microbial assemblage was discovered in Antarctic lake ice. Although this environment is marked by permanent ice cover, pockets of liquid water can form during part of the year, allowing active growth and reproduction of organisms.

Measuring and modelling the dynamic response of remote mountain lake ecosystems to environmental change: an introduction to the MOLAR project

Abstract: Because of their sensitivity, remote mountain lakes are not only vulnerable to environmental change, they are also excellent sensors of change, and their high quality sediment records can be used to infer the speed, direction, and biological impact of changing air quality and climate. The MOLAR project focuses on detailed studies of a smaller number of key sites to provide high resolution data on their temporal dynamics that can then be used to develop and calibrate predictive models.

Response of discharge and water quality in headwater brooks on distinct hydroclimatic conditions in the Tyrolean Alps

Abstract: Two headwater brooks within the UNESCO Biosphere Reserve in the crystalline Stubai Alps (north Tyrol, Austria) transport circumneutral waters with low conductivity (12-54 μS cm -1 ), low alkalinity (42-181 μeq l -1 ) and very low dissolved organic carbon (0.1-0.8 mg l -1 ). A perennial brook is gauged at its spring at 2450 m a.s.l. where low water temperatures (0-4°C) and very low discharge values (0.005-0.27 l s -1 ) prevail. Another brook is gauged at 2500 m a.s.l. below a small cascade, where water temperature and discharge vary between 0°C and 20°C, and 0 and 91 s -1 , respectively. This brook freezes during winter. The predominant ions calcium, sulphate and bicarbonate rise in the perennial brook at baseflow during winter, decline sharply during snowmelt but remain rather constant during summer rains. Whereas nitrate remains low (<30 μeq l -1 ) in the perennial brook throughout the year, nitrate concentrations in the ephemeral brook decrease from about 50 μeq l -1 during snowmelt to 25 μeq l -1 at the end of summer. Differing patterns in water chemistry, water temperature and flow regime indicate varying flow pathways for the investigated headwater brooks.