Microbial diversity and biosignatures of amorphous silica deposits in orthoquartzite caves

Francesco Sauro, Martina Cappelletti, Daniele Ghezzi, Andrea Columbu, Pei-Ying Hong, Hosam Mamoon Zowawi, Cristina Carbone, Leonardo Piccini, Freddy Vergara, Davide Zannoni, Jo De Waele

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40 Scopus citations


Chemical mobility of crystalline and amorphous SiO2 plays a fundamental role in several geochemical and biological processes, with silicate minerals being the most abundant components of the Earth's crust. Although the oldest evidences of life on Earth are fossilized in microcrystalline silica deposits, little is known about the functional role that bacteria can exert on silica mobility at non-thermal and neutral pH conditions. Here, a microbial influence on silica mobilization event occurring in the Earth's largest orthoquartzite cave is described. Transition from the pristine orthoquartzite to amorphous silica opaline precipitates in the form of stromatolite-like structures is documented through mineralogical, microscopic and geochemical analyses showing an increase of metals and other bioessential elements accompanied by permineralized bacterial cells and ultrastructures. Illumina sequencing of the 16S rRNA gene describes the bacterial diversity characterizing the consecutive amorphization steps to provide clues on the biogeochemical factors playing a role in the silica solubilization and precipitation processes. These results show that both quartz weathering and silica mobility are affected by chemotrophic bacterial communities, providing insights for the understanding of the silica cycle in the subsurface.
Original languageEnglish (US)
JournalScientific Reports
Issue number1
StatePublished - Dec 4 2018

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We would like to thank the Rector Prof. F. Ubertini, the Vice-Rector for Research Prof. A. Rotolo and the Governing Academic Bodies of the University of Bologna (UNIBO) for their support. This research has benefited from the permit for speleological research from the Instituto National de Parques and the patronage of the Government of Bolivar State from Venezuela, the Embassy of the Bolivarian Republic of Venezuela in Italy and the Italian Speleological Society. The project received economic support of many private sponsors to whom we are deeply grateful: Rolex Award for Enterprise, Raul Arias with Raul Helicopteros, Geotec S.P.A., Dolomite, Intermatica, Ferrino, Napapijri, De Walt, Scurion, Miles Beyond and Allemano Metrology. Our gratitude goes also to the speleologists from Theraphosa and La Venta exploring teams, to Prof. E. Dinelli for XRF analyses at UNIBO and L. Negretti for the SEM analysis at UNIGE. Many thanks also to T. Conte who supported the 2013 and 2014 expeditions and to T. Bontognali for the useful suggestions on the manuscript. Two anonymous reviewers significantly contributed to improve the quality of the article by sharing constructive remarks.


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