Nature has been synthesising sustainable, durable and self-healing materials in ambient conditions in a carbon neutral or even carbon negative way for millions of years, via the process of biomineralization. Caves represent one such class of CO2 sequestering biomineralized environment wherein complex interplay of physical, environmental, microbial and mineralogical interactions lead to formation of biomineralized structures called as speleothems. In the current study, we characterized cave speleothems from three caves for their microbial, mineralogical and mechanical properties with the aim of understanding the complex relationships between microbial, mineralogical and nanomechanical properties of naturally biomineralized materials.
The results showed that all speleothem surfaces had high ATP activity. Lake cave speleothems revealed higher amounts of Sulfur, Iron, Magnesium and Aluminium metals compared to other caves which had higher Calcium. Microbial diversity revealed significant variations within same caves as well as amongst different cave speleothems. Proteobacteria and Actinobacteria were seen to be dominant in all speleothems while Lake cave speleothems had significantly higher Acidobacteria. Several bacterial isolates which have been earlier related to play an active role in biomineralization were seen in all speleothems while their dominance was seen in case of Moondyne cave speleothems. Scanning electron micrographic results highlighted bacterial imprints and hyphae in all speleothems indicating their potential associations. Mineralogical analysis was carried out by X ray diffraction, Energy dispersive spectroscopy and Tescan Integrated Mineral Analyzer (TIMA) which showed different polymorphs of calcium carbonate (mainly calcite) in all specimens. The microbial data was seen to be closely associated with geochemistry and mineralogical components of speleothems. Moondyne cave speleothems which had dominance of biomineralizing microbial communities also had higher calcite indicating some connections in between the two. Nanoindentation analysis also revealed that speleothems which had higher calcite and biomineralizing microbes had higher strength properties. This study hints plausible role of microbial-mineralogical signatures on mechanical properties of biomineralized formations but, more studies on fossilized microbes within different biomineralized natural formations are required.