Speleothems are secondary mineral deposits normally formed by water supersaturated with calcium carbonate percolating into underground caves, and are often associated with low-nutrient and mostly non-phototrophic conditions. Tjuv-Ante's cave is a shallow-depth cave formed by the action of waves, with granite and dolerite as major components, and opal-A and calcite as part of the speleothems, making it a rare kind of cave. We generated two DNA shotgun sequencing metagenomic datasets from the interior of a speleothem from Tjuv-Ante's cave representing areas of old and relatively recent speleothem formation. We used these datasets to perform i) an evaluation of the use of these speleothems as past biodiversity archives, ii) functional and taxonomic profiling of the speleothem's different formation periods, and iii) taxonomic comparison of the metagenomic results to previous microscopic analyses from a nearby speleothem of the same cave. Our analyses confirm the abundance of Actinobacteria and fungi as previously reported by microscopic analyses on this cave, however we also discovered a larger biodiversity. Interestingly, we identified photosynthetic genes, as well as genes related to iron and sulphur metabolism, suggesting the presence of chemoautotrophs. Furthermore, we identified taxa and functions related to biomineralization. However, we could not confidently establish the use of this type of speleothems as biological paleoarchives due to the potential leaching from the outside of the cave and the DNA damage that we propose has been caused by the fungal chemical etching.
Notes
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The resi Its of investigation of speleothem (moonmilk) from the Snezhnaya cave (West Caucasus, Abkhazia) are-reported. The structure of microbial complexes from moonmilk was investigated by quantita- tive 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 bacte- rial strains were shown to be facultative psychrophiles with the maximum growth rate at 4C. The microstruc- ture and elemental composition of mionmilk were investigated using a scanning electron microscope (EVO- 40HV, Carl Zeiss) and silicon drifi X-ay detector X-MAX 80 ffM2' 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. Calcium content was high, up to 61.5% (wt/wt) only in cubic crystalline structures which were not involved in microbiological processes.
The resi Its of investigation of speleothem (moonmilk) from the Snezhnaya cave (West Caucasus, Abkhazia) are-reported. The structure of microbial complexes from moonmilk was investigated by quantita- tive 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 bacte- rial strains were shown to be facultative psychrophiles with the maximum growth rate at 4C. The microstruc- ture and elemental composition of mionmilk were investigated using a scanning electron microscope (EVO- 40HV, Carl Zeiss) and silicon drifi X-ay detector X-MAX 80 ffM2' 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. Calcium content was high, up to 61.5% (wt/wt) only in cubic crystalline structures which were not involved in microbiological processes.
