Microbial Biscuits of Vaterite in Lake Issyk-Kul (Republic of Kyrgyzstan)—Discussion

FIG. 1.—Possible metabolic pathways leading to carbonate precipitation in bacteria. AA, amino-acids; TCA, tricarboxylic acid cycle; GA, glyoxylic acid cycle. Giralt et al. (2001) reported the formation of microbial biscuits of vaterite in Lake Issyk-Kul (Republic of Kyrgyzstan). Although they state that the trigger mechanisms for the natural precipitation of vaterite remain unclear, they propose an explanation of the origin for the vaterite biscuits involving bacterial activity. Our recent research seems to support their hypothesis, although the way we obtain vaterite precipitation is not strictly related to lacustrine or natural aqueous environments. We have used laboratory cultures to demonstrate the ability of some soil bacteria to transform an oxalate carbon source into carbonate, a hypothesis supported by observations (Cromack et al. 1977; Verrecchia et al. 1993) and biogeochemical studies (Verrecchia and Dumont 1996). The bacteria