New On Nature.com: Microbial Mediation Of Complex Subterranean Mineral Structures
Published online on October 29, 2015 by Scientific Reports, this article by Nicola Tisato (University of Toronto, Canada), Stefano F. F. Torriani (Institute of Integrative Biology, Switzerland), Sylvain Monteux (Université Montpellier 2, France), Francesco Sauro, Jo De Waele and Ilenia M. D’Angeli (Bologna University, Italy), Maria Luisa Tavagna, Timothy I. Eglinton and Tomaso R. R. Bontognali (ETH Zurich, Switzerland) and Daniel Chailloux and Michel Renda (FFS –Fédération Française de Spéléologie, France) is now available to view.
Helictites—an enigmatic type of mineral structure occurring in some caves—differ from classical speleothems as they develop with orientations that defy gravity. While theories for helictite formation have been forwarded, their genesis remains equivocal. Here, we show that a remarkable suite of helictites occurring in Asperge Cave (France) are formed by biologically-mediated processes, rather than abiotic processes as had hitherto been proposed. Morphological and petro-physical properties are inconsistent with mineral precipitation under purely physico-chemical control. Instead, microanalysis and molecular-biological investigation reveals the presence of a prokaryotic biofilm intimately associated with the mineral structures. We propose that microbially-influenced mineralization proceeds within a gliding biofilm which serves as a nucleation site for CaCO3, and where chemotaxis influences the trajectory of mineral growth, determining the macroscopic morphology of the speleothems. The influence of biofilms may explain the occurrence of similar speleothems in other caves worldwide, and sheds light on novel biomineralization processes.