Calcium carbonate precipitation by oxalate degrading
bacteria
Olivier
Braissant, Ph.D. student
The
influence of microbes on the precipitation and dissolution of
minerals has been known for a long time. The case of calcium oxalate
is particularly interesting because calcium-oxalate is present
in many biological systems and plays an important role in biogeochemical
cycles and in some humans diseases, such as kidney stones. Despite
the poor solubility of metal-oxalate complexes and the high oxidation
degree of oxalate, about 40 bacteria species are known to dissolve
and use Ca-oxalate as a carbon source.
Aerobic
degradation of oxalates leads to the formation of carbonate ions,
which will react with calcium released during the consumption
of calcium oxalate by bacteria. The transformation of oxalate
into carbonate results in a pH increase which allows the calcium
carbonate precipitation. During our study of the oxalate-carbonate
cycle, we investigated the production of calcium carbonate by
oxalate-degrading bacteria. Some strains produce mainly calcite,
whereas other strains preferentially produce vaterite a polymorph
of calcium carbonate. It seems that exopolysaccharides (EPS) and
some types of homo- or hetero-polypeptides are strongly linked
to the differential calcium carbonate crystallization.
Vaterite
samples similar to those produced by our cultured bacteria have
recently been found in nature for the first time. This recent
discovery combined with our results emphasizes the critical role
of microorganisms in carbonate precipitation by their direct influence
on local pH and therefore by controlling the conditions underwhich
carbonate precipitates.
Links to some of my other interests:
http://www.unil.ch/igbm/Congres/SSM_2001/Braissant_2001.html
http://www.unil.ch/igbm/Vu_dans_la_Presse/24h_990717.html
http://www.unil.ch/igbm/genomics/genometrics.html
http://www.unil.ch/igbm/Congres/Bern_1999/1st_swiss_exobiol_workshop.html
http://www.estec.esa.nl/outreach/parabollic/results_from_3rd_pfc.htm
http://www.estec.esa.nl/outreach/parabollic/pictures_from_3pfc.htm
Last
Update : Feb. 2002
