Tufa-forming biofilms of German karstwater streams: microorganisms, exopolymers, hydrochemistry and calcification - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 80

Tufa-forming biofilms of German karstwater streams:
microorganisms, exopolymers, hydrochemistry and calcification
GERNOT ARP 1 *, ANDREW BISSETT 2† , NICOLE BRINKMANN 3 , SYLVIE COUSIN 4# ,
DIRK DE BEER 2 , THOMAS FRIEDL 3 , KATHRIN I. MOHR 3‡ , THOMAS R. NEU 5 ,
ANDREAS REIMER 1 , FUMITO SHIRAISHI 1§ , ERKO STACKEBRANDT 4 &
BARBARA ZIPPEL 5
1 University of G¨ttingen, Geoscience Centre, Goldschmidtstraße 3, D-37077
G¨ ttingen, Germany
2 Max Planck Institute for Marine Microbiology, Celsiusstraße 1, D-28359 Bremen, Germany
3 University of G¨ ttingen, Albrecht-von-Haller-Institute for Plant Sciences,
Experimental Phycology and Culture Collection of Algae (SAG), Nikolausberger Weg 18,
D-37073 G¨ ttingen
4 German Collection of Microorganisms and Cell Cultures DSMZ, Inhoffenstraße 7 B,
D-38124 Braunschweig, Germany
5 Helmholtz Centre for Environmental Research UFZ, Department of River Ecology,
Br¨ckstraße 3a, D-39114 Magdeburg, Germany
† Present address: CSIRO, Plant Industry, P. O. Box 1600, Canberra, ACT 2601, Australia
‡ Present address: Helmholtz Centre for Infection Research, Inhoffenstraße 7, D-38124
Braunschweig, Germany
§ Present address: Division of Evolution of Earth Environment, Graduate School of
Social and Cultural Studies, Kyushu University, 744 Motooka, Nishi-ku,
Fukuoka 819-0395, Japan
# Institut Pasteur, Genopole de l'Ile de France, PF1, Paris, France
*Corresponding author (e-mail: [e-mail])
Abstract: To understand mechanisms of tufa biofilm calcification, selected karstwater stream
stromatolites in Germany have been investigated with regard to their hydrochemistry, biofilm com-
munity, exopolymers, physicochemical microgradients, calcification pattern and lamination. In
stream waters, CO 2 degassing drives the increase in calcite saturation to maximum values of
approximately 10-fold, independent from the initial Ca 2þ /alkalinity ratio. For the cyanobacteria
of tufa biofilms, a culture-independent molecular approach showed that microscopy of resin-
embedded biofilm thin sections underestimated the actual diversity of cyanobacteria, i.e. the six
cyanobacteria morphotypes were opposed to nine different lineages of the 16S rDNA phylogeny.
The same morphotype may even represent two genetically distant cyanobacteria and the closest
relatives of tufa biofilm cyanobacteria may be from quite different habitats. Diatom diversity
was even higher in the biofilm at the studied exemplar site than that of the cyanobacteria, i.e. 13
diatom species opposed to 9 cyanobacterial lineages. The non-phototrophic prokaryotic biofilm
community is clearly different from the soil-derived community of the stream waters, and
largely composed of flavobacteria, firmicutes, proteobacteria and actinobacteria. The exopoly-
meric biofilm matrix can be divided into three structural domains by fluorescence lectin-binding
analysis. Seasonal and spatial variability of these structural EPS domains is low in the investigated
streams. As indicated by microsensor data, biofilm photosynthesis is the driving mechanism in tufa
stromatolite formation. However, photosynthesis-induced biofilm calcification accounts for only
10 - 20% of the total Ca 2þ loss in the streams, and occurs in parallel to inorganic precipitation
driven by CO 2 -degassing within the water column and on biofilm-free surfaces. Annual stromato-
lite laminae reflect seasonal changes in temperature and light supply. The stable carbon isotope
composition of the laminae is not affected by photosynthesis-induced microgradients, but