Lab Features

The alpine station Cadagno, Centro biologia alpina, in the Swiss alps

View of the lab building of the CBA

Ten years ago, two old cattle shelters at 1964 m above sea level in the Swiss alps have been transformed into a modern biological alpine station. Together with rooms in another building nearby, the station has several laboratories, seminar rooms and can house over 50 researchers or students. The station is situated close to a small, very specific lake: Lake Cadagno. It is one of the few crenogenic meromictic lakes in Europe. While the region, including its many lakes, has been studied by some natural scientists in the 19th and early 20th century already, detailed research on the biology and chemistry of Lake Cadagno started in the 1980ies only. Students and researchers from the microbiological laboratory of the State of Tessin (housing the laboratory of microbial ecology of the University of Geneva) and the University of Zurich studied the annual cycle of the main chemical components in the water and the occurence of the dominant, easiliy visible purple phototrophic bacterium, Chromatium okenii. Sampling was achieved even in winter time, when field work was rendered rather difficult by several meters of snow and ice. Since then, many different aspects of the lake's chemistry and microbiology have been tackled, as can be seen from the reference list. The biological alpine station soon became a preferred site for a variety of student courses, mainly from the Universities of Geneva and Zurich. More recently, specific courses have been organized with international partners, e.g. the Max Planck Institute for Marine Microbiology in Bremen (Germany), the University of Essen (Germany) and the University of Paris (France). On a more educational level the station housed many groups from Swiss colleges, introducing young students into environmental aspects of lake chemistry and biology. The station is controlled by a foundation and managed by the Microbiology laboratory of the state of Tessin.

Phototrophic and sulfate reducing bacteria forming aggregates catalyzing the full sulfur cycle

The chemistry of the lake and the nearby wetlands are governed by the geology of the Piora valley, a trough of basic Dolomite containing gypsum surrounded by acidic Granite. Rain water penetrating the gypsum leaches mainly carbonate, sulfate, calcium and magnesium. Subsurface springs bring such ion-rich and dense water into the lake and low mineral water from the acidic rocks enters the lake at the surface. This results in two water layers distinctly separated, typical for meromictic lakes. At the chemocline between the anoxic bottom water and the oxic surface water, separating the two water masses, a rich population of phototrophic and sulfate reducing bacteria develops, catalysing a full reduction-oxydation cycle of sulfur from sulfide to sulfate (phototrophs) and reverse (SRB).

In the nearby wetlands a similar bacterial consortium forms microbial mats showing the same physiology as the bacterial layer in the lake. A further, very fascinating microbial ecosystem is found in endolithic bacteria on bare Dolomite rock, often met in the Piora vallley.

Microbial mats in wetlands west of Lake Cadagno, white precipitation of elemental sulfur

Microbial mat in wetlands west of Lake Cadagno cut off to demonstrate the layer of cyanobacteria and purple phototrophic bacteria

Microbial mat in Lake Cadagno at 6 to 8 m depth showing cyanobacteria, purple phototrophic bacteria and white precipitations of elemental sulfur

 

Highlights on some recent findings:
In situ measurement of sulfide turnover in the bacterial layer of the lake:
Using the push-pull technique in the open water, the in situ oxydation of and the reduction to sulfide has been determined under real field conditions. Sodium sulfide is injected into the bacterial layer and recovered after a defined time interval. The varying ratio of sodium to sulfide indicated either an oxydation of sulfide (at day time in the upper part of the bacterial layer) or its reduction (at night and in deeper zones of the lake), from which turnover rates can be calculated (Appl. Environm. Microbiol. 66, 712-717, 2000).

Diurnal movements of the bacterial layer of the lake:
With electronic sensors for turbidity and temperature the distribution of the mass of the bacteria was followed at a high sampling rate. The fluctuations in temperature gave evidence for large physical displacements of the bacterial layer, but they were used to distinguish passive mass transport of the cells from their light induced daily active vertical movement of the cells. Daily active movements were in the range of 20 to 30 cm (Aquatic Microbial Ecology 35, 105-113, 2004).

Biodiversity of the endolithic microbial population in Dolomite:
Reflection spectroscopy, confocal laser scanning microscopy, pigment analysis as well as the study of the16S rDNS revealed a rich population of phototrophic and heterotrophic bacteria in the thin bacterial layer situated a few mm below the rock surface. Main producers were coccoid and filamentous cyanobacteria. An in situ absorption at 720 nm with a corresponding spectrum after HPLC separation of the pigments suggested a new type of bacteriochlorophyll. (unpublished and Environm. Microbiol. 5, 618-627, 2003).

 

Phylogeny and distributions of the purple sulfur bacteria from the chemocline of the lake:
A 16S rDNA based clone library obtained from samples from the chemocline and the anoxic monimolimnion of the meromictic Lake Cadagno allowed the development of specific oligonucleotide probes and accurate FISH distribution analysis of purple sulfur bacteria populations in the chemocline. Small celled phototrophs belonging to the genus Lamprocystis consisted of four distinct phylotypes showing different depth distribution patterns (Appl. Environm. Microbiol. 65: 1325-1330, 1999) and different biomass values over an annual cycle (FEMS Microbiology Ecology 1415: 1-10, 2003)

FISH of sample from the bacterial layer using DAPI and the specific probe for Amoebobacter

 

Spatio-temporal distribution, isolation and characterisation of aggregate-forming sulfate-reducing and purple sulfur bacteria:
As much as 35 to 45% of the total microbial community in the chemocline was found to be associated in aggregates consisting of small-celled purple sulfur bacteria (Lamprocystis spp.) and of sulfate-reducing bacteria (Desulfocapsa spp.). our work allowed for an in situ vertical and temporal analysis with specificly developped probes as well as isolation and characterisation of both partners of the aggregates (Appl. Environm. Microbiol 66: 820-824, 2000, Aquatic Microbial Ecology 30: 295-302, 2003 and FEMS Microbiology Ecology 45: 29-37, 2003)

Population dynamics of phototrophic sulfur bacteria over a decade:
In situ hybridization with specific oligonucleotide probes was used to monitor population dynamics of phototrophic sulfur bacteria in the chemocline of the meromictic Lake Cadagno, Switzerland, over a period of 10 years (1994-2003). C. okenii was prominent in the beginning of the monitoring period. The initial importance of C. okenii, however, was replaced by populations of small-celled purple bacteria that were abundant between 1994 and 2001. After 2001, the numbers of green sulfur bacteria increased significantly and became dominant. These population dynamics could be correlated with environmental conditions in the water column, which may be caused by extreme weather events (storms) recorded in the autumn of the years 1999 and 2000. (Unpublished results, paper submitted to Appl. Environm. Microbiol)

Molecular identification of an uncultured bacterium ("morphotype R") in the deep monimolimnion:
Comparative sequence analysis of 16S rRNA genes of members of the Desulfobacteriaceae retrieved from the monimolimnion resulted in the molecular identification of nine sequences related to Desulfomonile tiedjei and D. limimaris, respectively. In situ hybridization with specific probes targeting different subpopulations detected bacteria with a peculiar morphology previously described as "morphotype R". In the monimolimnion, "morphotype R" cells accounted for up to 29% of all Bacteria and fully represented the Desulfobacteriaceae, the most prominent group of sulfate-reducing bacteria. Their population profiles positively correlated with sulfide concentration and redox potential. In the sediment, "morphotype R" was similarly prominent in the upper cm only, where it represented all Desulfobacteriaceae and up to 50% of all Bacteria (J. Limnol., 63: 157-166, 2004 and unpublished results submitted to FEMS Microbiology Ecology).

Spatial dynamic of sulfate-reducing bacteria, methanogens, TOC, THAA and amino acids in the anaerobic sediments of Lake Cadagno and Rotsee:
A combined molecular and chemical approach investigated the coexistence of sulfate-reducing bacteria and methanogens in sediments dominated by sulfate-reduction (Lake Cadagno) and methanogenesis (Rotsee). The bioavailable fraction of organic matter was analysed in detail. The amount of sedimentary organic carbon (TOC) and total hydrolyzable amino acids (THAA) was two-fold higher in Lake Cadagno compared to Rotsee. TOC and THAA values could be partially correlated to the microbial counts. Bacteria represented on average 28% and 25%, sulfate-reducing bacteria 19 and 5%, and Archaea 9% and 2% of the microbial communities at Lake Cadagno and Rotsee, respectively. Lake Cadagno showed two pronounced zones of microbial activity, whereas in the Rotsee the highest microbial density was identified in the uppermost sediment layers (Unpublished results).

Participants of the summer course 2003 in molecular microbial ecology
Participants of the summer course 2004 in molecular microbial ecology

 

Further Information:

http://www.cadagno.ch
http://www.ti.ch/DSS/DSP/ISTCM/CBA-piora/
http://www.unicom.unizh.ch/journal/archiv/3-99/piora.html
http://www.unizh.ch/~horath/cadagno.html
http://www.biuz.unizh.ch/keimblatt/wandzeitung/cadagno.html
http://www.unicom.unizh.ch/journal/archiv/1-99/mikroorganismen.html
http://www.research-projects.unizh.ch/math/unit71500/area329/p948.htm
http://www.mpi-bremen.de/molecol/fog/images/planktonic.pdf
http://supprem.unige.ch/docs/piora/
http://www.ti-edu.ch/usu/ticampus99/ita/biologia/biologia.htm

Contact:

Prof. Dr. Reinhard Bachofen
University of Zurich, Switzerland
Institute of Plant Biology
bachofen@botinst.unizh.ch