Role of the microbial community in formation of speleothem (moonmilk) in the Snezhnaya carst cave (abkhazia)

Abstract

The results of investigation of speleothem (moonmilk) from the Snezhnaya cave (West Caucasus, Abkhazia) are reported. The structure of microbial complexes from moonmilk was investigated by quantitative PCR; strains of culturable microorganisms were isolated and their preferred temperature and carbon sources were determined. Among eubacteria, ~34% belonged to the iron bacteria (Rhodoferax). Most bacterial strains were shown to be facultative psychrophiles with the maximum growth rate at 4°C. The microstructure and elemental composition of moonmilk were investigated using a scanning electron microscope (EVO-40HV, Carl Zeiss) and silicon drift X-ray detector X-MAX 80mm². The visually plastic and homogeneous mass of moonmilk was shown to be highly heterogeneous, containing various microstructures. The elemental composition of some nanostructures depended on the structure of bacterial biofilms. Some loci of the biofilm were found to contain up to 46% (wt/wt) of iron oxides. High calcium content, up to 61.5% (wt/wt), was found only in cubic crystalline structures which were not involved in microbiological processes.