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TZUNTIL:20070325T010000Z
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DTSTART:20041031T030000
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RDATE:20051030T030000
RDATE:20061029T030000
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UID:www.bayceer.uni-bayreuth.de-bayceer-t53290id
DTSTAMP:20260919T082426Z
DESCRIPTION:Cyanobacteria are photosynthetic prokaryotes commonly found in 
 soils and freshwater. They are also an important component of marine phyto
 plankton and contribute significantly to the overall primary production in
  ecosystems of all climatic zones. Cyanobacteria often dominate the picopl
 ankton (cell diameter  0.2 -2 um) community in oligotrophic systems. Picoc
 yanobacteria are increasingly investigated due to their ecological signifi
 cance. Recent studies indicate that picoplankton plays an important role i
 n calcite precipitation in oligotrophic lakes. However\, the mechanism of 
 calcite precipitation on picocyanobacteria is still unclear. In this prese
 ntation I will show the results of our studies on the role of picoplankton
  for CaCO3 precipitation. Our studies include field observations and diffe
 rent kinds of laboratory experiments.\nWe provide field observations in or
 der to correlate spatial and temporal patterns of picoplankton abundance a
 nd calcite precipitation in Lake Lucerne. Seasonal calcite concentration p
 eaks in oligotrophic lakes may be explained by the activity of unicellular
  autotrophic picocyanobacteria. In a pre-study we investigated the cell mi
 neral interface by analytical Transmission Microscopy (TEM). For this anal
 ysis samples were prepared using a Focused Ion Beam (FIB)-milling. From th
 ese experiments we concluded that the composition of the cell surface seem
 s to play a crucial role in the nucleation process. In order to investigat
 e the nucleation of calcite on the cell surface\, experiments under contro
 lled conditions were performed in a flow-through design of an AFM as well.
 \nIn the most recent study\, the surface properties of two picocyanobacter
 ia strains were examined by measurements of zeta potential\, potentiomentr
 ic titration\, and infrared spectroscopy (IR). The results demonstrated th
 at the deprotonation of picocyanobacterial cells surfaces is a reversible 
 process. Modelling results\, data on zeta potential and IR spectra are con
 sistent with the presence of three surface sites\, corresponding to carbox
 yl\, phosphate\, and amine groups. The carboxyl group slightly dominates t
 he surface sites in both strains with 37% and 44%\, the amine groups repre
 sent 36% and 29%. The smaller fraction of phosphate was similar in both st
 rains with 27% and 26%.\nDuring the picocyanobacterial bloom in oligotroph
 ic lakes the concentration of functional groups amounts to ca. 0.35 mmol/m
 l. The zeta potential measurements have shown that picocyanobacteria are n
 egatively charged at pH between 6 and 7\, which is typical for natural sur
 face water. Calcium cations can therefore be easily attracted. On the othe
 r hand\, the presence of amine groups on the cell surface influences the c
 arbonate anions. Both reactions are important in the nucleation of calcite
  on the cell and may be key processes for the calcite precipitation in lak
 es.
DTSTART;TZID=Europe/Berlin:20050503T170000
DTEND;TZID=Europe/Berlin:20050503T235959
LOCATION:H6
SUMMARY:Dr. Maria Dittrich\, Forschungszentrum für Limnologie\, EAWAG\,Kast
 anienbaum\, Schweiz: CaCO3 precipitation by cyanobacteria: insights from f
 ield\, laboratory and microscopic studies.
TRANSP:TRANSPARENT
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