The preservation and degradation of filamentous bacteria and biomolecules within iron oxide deposits at Rio Tinto, Spain

Abstract

One of the keys to understanding and identifying life on other planets is to study the preservation of organic compounds and their precursor micro-organisms on Earth. Rio Tinto in southwestern Spain is a well documented site of microbial preservation within iron sulphates and iron oxides over a period of 2.1 Ma. This study has investigated the preservation of filamentous iron oxidising bacteria and organics through optical microscopy, scanning electron microscopy (SEM) and Fourier transform infra-red (FTIR) spectroscopy, from laboratory cultures of natural samples to contemporary natural materials to million-year old river terraces. Up to 40% elemental carbon and >7% nitrogen has been identified within microbial filaments and cell clusters in all samples through SEM EDS analyses. FTIR spectroscopy identified C-H(x) absorption bands between 2960 and 2800 cm(-1), Amide I and II absorption bands at 1656 and 1535 cm(-1), respectively and functional group vibrations from within nucleic acids at 917, 1016 and 1124 cm(-1). Absorption bands tracing the diagenetic transformation of jarosite to goethite to hematite through the samples are also identified. This combination of mineralogy, microbial morphology and biomolecular evidence allows us to further understand how organic fossils are created and preserved in iron-rich environments, and ultimately will aid in the search for the earliest life on Earth and potential organics on Mars.

Potential Role of Nitrite for Abiotic Fe(II) Oxidation and Cell Encrustation during Nitrate Reduction by Denitrifying Bacteria

“…Our study suggests that the Fe(III) minerals encrusting the nitrate reducers are probably a metabolic by-product of heterotrophic nitrite formation. Partly and fully mineralized cells have been detected in Fe(II)-rich rivers and springs (72,73), even with the very unique formation of a layer rich in iron and organic material, similar to the ones observed in our study ( Fig. 5B; also, see the supplemental material) (74).…”

Interpreting melanin-based coloration through deep time: a critical review

“…Moreover, microbes are always associated with decaying carcasses, and are known to fossilize as both organic (e.g. [15,16]) and inorganic traces (e.g. [17]).…”

Preserved Filamentous Microbial Biosignatures in the Brick Flat Gossan, Iron Mountain, California

“…The morphological parameters measured were (1) filament or fiber diameter, (2) tortuosity, (3) bending (degrees/20 lm), and (4) number of direction changes/20 lm. These parameters were measured on (1) microbial and mineral filaments from Iron Mountain and (2) microbial filaments from the literature: three Iron Mountain gossan samples with microbial filaments (N = 20 microbial filaments), seven examples of microbial filaments from the literature (Seeger and Jerez, 1993;Schrenk et al, 1998;Edwards et al, 1999;Gumaelius et al, 2001;Schieber and Glamoclija, 2007;Florea et al, 2011;Preston et al, 2011) (N = 22 microbial filaments), one halotrichite group mineral salt sample from Iron Mountain (N = 10 fibers), one Iron Mountain sample with cryptic filaments (N = 12 cryptic filaments), one Iron Mountain sample with central filament lumina (N = 6 lumina), and eight Iron Mountain samples with HFO filaments (N = 318 HFO mineral filaments).…”

“…Numerous studies have explored how mineralized biosignatures form and are preserved in iron and silica systems ( Juniper and Fouquet, 1988;Cady and Farmer, 1996;Fortin et al, 1997;Hofmann and Farmer, 2000;Banfield et al, 2001;Kennedy et al, 2004;Little et al, 2004;Fortin and Langley, 2005;Hofmann et al, 2008;Parenteau and Cady, 2010;Preston et al, 2011;Peng and Jones, 2012). Filaments composed of minerals have been interpreted as mineralcoated filamentous microbes in a range of environments including hydrothermal veins, volcanic settings, base-metal deposits, and oxidizing ore bodies (Cady and Farmer, 1996;Hofmann and Farmer, 2000;Banfield et al, 2001;Jones et al, 2001;Hofmann et al, 2008;Jones, 2010;Preston et al, 2011;Peng and Jones, 2012).…”

“…Filaments composed of minerals have been interpreted as mineralcoated filamentous microbes in a range of environments including hydrothermal veins, volcanic settings, base-metal deposits, and oxidizing ore bodies (Cady and Farmer, 1996;Hofmann and Farmer, 2000;Banfield et al, 2001;Jones et al, 2001;Hofmann et al, 2008;Jones, 2010;Preston et al, 2011;Peng and Jones, 2012).…”