Diversity of Cyano-Bacterial Mats

Abstract

Sustainable existence of biotic systems depends on their fitness to environment, which means minimal changes caused by their activity in habitat. Otherwise changed environment will call to existence another biocoenosis fitted to it, as it occurs during succession. This statement is to some extent opposite to the Gaian idea of reshaping environment by biota to its own benefits. Cyano-bacterial community is the most sustainable biotic system, that dominated Earth from Early Proterozoic to the end of Neoproterozoic revolution and still survives in habitats from which it is not expelled by its successors (Sergeev at all. 1998). Throughout this time cyano-bacterial community transformed the Earth surface to what represents now the biosphere but despite all changes was able to survive thanks to close combining productive cyanobacterial and destructive bacterial components of the biogeochemical cycles. This is a reason why both groups of prokaryotes, photoautotrophic and organotrophic, should be included in the definition of cyano-bacterial community, being designated by the hyphen (Stal, Caumette, 1993). Cyanobacterial productive component depends on light, CO2, and phosphorus with C:P ratio 100. Equimolar ratio of photoautotrophic assimilation CO2:O2:Corg=1:1:1 represents the main driving force of Corg cycle in the biosphere (fig.1). Bioticaly mediated cycle of O2 causes the oxidative transformation of the biosphere due to the inability of decomposing organotrophs to utilize all Corg produced. Part of Corg is buried during the sedimentary process as kerogen, representing undecomposed mortmass together with amorphous humic substances (Tyson, 1999). Equimolar quantity of O2 is liberated and involved in oxidative branches of S and Fe cycles driven exclusively by prokaryotes with production and deposition of inert Fe-oxides and oceanic sulphates as O2 sink (Schidlowski, 1993). Partially biologically mediated is inorganic CO2-sink driven by Cacarbonate-silicate weathering chain (for bibliog. see Schwartzman, 1999) leading to formation of carbonate deposits and production of clays as sustainable residual substances. Mortmass and kerogen are buried in clays during the sedimentary processes. Carbonate deposits of Proterozoic are obviously linked to cyanobacterial communities by formation of stromatolites. Geochemical calcium cycle is responsible for the neutrophilic conditions on the Earth and it is amplified by biologically mediated reactions, in Proterozoic — driven by microbes exclusively (Zavarzin, 2002).