Biology
Scientific paper
Oct 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009asbio...9..777k&link_type=abstract
Astrobiology, Volume 9, Issue 8, pp. 777-796.
Biology
1
Bacteria, Banded Iron Formation, Microbe-Mineral Interactions, Iron-Reducing Bacteria, Microbial Fossils, Cellular Fossilization
Scientific paper
We report here on magnetite- and wustite-encrusted and geometrically oriented microbial-like structures (MLS) attached to the surfaces of hematite (α-Fe2O3) crystals in a banded iron formation. Field emission scanning electron microscope (FE-SEM) and scanning electron microscope (SEM) imaging showed a 3-D network of MLS arranged in 1 μm- 20 μm coccoidal-like chains (CLC) of various geometrical shapes: dichotomous and budding-like protrusions, parallel, intersecting, triangular, or sinusoidal. Individual spheroidal forms (˜1 μm in diameter), some displaying what appears to be division, were also abundant. In addition to their size, morphology, and preferred orientations, a microbial origin of these chains and single spheroidal forms is inferred by the presence of material that resembles extracellular polymeric substances (EPS) extending from the base of the chains along the mineral surface: the attachment sites show circular dissolution pits of about 100 nm diameter. Other thin structures protruding from the CLC are reminiscent of bacterial "nanowires." We were, however, unable to find any extant cells, organic carbon, or even recover DNA from the MLS, which suggests that they, if microbial, are possibly mineralogically replaced casts or mineral encrustations of cells. It is further speculated that, given the nature of the substrate upon which the forms are attached and their preferential orientations, it seems plausible that the "original cells" may have been Fe(III)-reducing bacteria that exploited structural imperfections in the crystal lattice. Importantly, the preservation of the ancient microbial shapes in mineral casts of magnetite, wustite, or both may be an overlooked means by which cellular features in the rock record are retained.
Claeys Philippe
Hubin Annick
Kolo Kamal
Konhauser Kurt
Krumbein Wolfgang Elisabeth
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