Fig 1.
The iron sulfide mineralization of Thermococcales cells and vesicles (MVs).
(A) Scanning electron microscopy image of T. prieurii cells and vesicles mineralized and organized in aggregates. Every sphere observed can be a mineralized cell (from 0.8 μm to 1.4 μm) or a vesicle (up to 0.5 μm). Scale bar = 1μm. (B)Transmission electron microscopy image of T. prieurii cells and vesicles entirely mineralized incubated for 168 hours with mineralization medium (“a” indicates the location of the EDXS analysis); scale bar = 500nm; (C) and elemental analysis by EDXS; with Fe/S ratio of about 0.5. Cu peaks are derived from the supporting grid. (D) Electron diffraction pattern of the minerals of the cell surfaces and/or filling, corresponding to pyrite. This is a polycrystalline pattern with strong preferred orientations toward a common 2–11 zone axis. (E) Transmission electron microscopy image of numerous extracellular greigite nanocrystals (indicated by black arrows) located near a vesicle containing pyrite (indicated by a red arrow); scale bar = 100nm (F) and near a cell; about fifty nanocrystals were counted to obtain the 30–70 nm range; scale bar = 100nm.
Fig 2.
Nanocrystals of Fe3S4 greigite.
(A) Transmission electron microscopy image of greigite nanocrystals. Scale bar = 50nm. (“a” indicates the location of the EDXS analysis) (B) and elemental analysis by EDXS; with Fe/S ratio of about 0.75. Cu peaks are derived from the supporting grid. (C) Scanning transmission electron microscopy image of greigite nanocrystals (indicated by black arrows) dispersed in mineralized extracellular polymeric substances and associated Fe (middle panel) and S maps (lower panel). Scale bar = 200nm. (D) Electron diffraction of a greigite crystal. (E) High-resolution transmission electron microscopy image of a greigite nanocrystal. The inter-reticular distances at 5.7 and 3.5 Angstrom correspond respectively to {111} and {220} sets of lattice planes; the image thus has a <110> zone axis. Scale bar = 5nm.
Fig 3.
The first stages of greigite mineralization of Thermococcales.
(A) Scanning and transmission electron microscopy images of T. prieurii cells incubated for 5 hours; scale bar = 2μm, (B) 24 hours; scale bar = 200nm and (C) 48 hours; scale bar = 100nm with mineralization medium and their respective elemental analyses by EDXS (A(i), B(i), C(i)). Cu and Ni peaks are derived from the supporting grid. For each microscopy images, the black arrow indicates the location of the EDXS analysis. The first minerals formed on the cell surfaces correspond to amorphous Fe(III) phosphates (A, B). The Thermococcales S-layer is the highly reactive interface for iron sequestration (B). After 48 hours of incubation in mineralization medium, Thermococcales cells release extracellular polymeric substances mineralized with amorphous iron phosphates (C).
Fig 4.
The phosphate to greigite mineralization process.
Transmission electron microscopy image; scale bar = 100nm; and EDXS spectra of nanocrystals of greigite (a) dispersed in the organic matrix mineralized with amorphous Fe(III) phosphates (b) located near the sulfur vesicles of T. prieurii (c). The lettering indicates the location of the spot scan for the EDXS analyses. (A) EDXS spectrum of a greigite crystal showing iron and sulfur peaks; Fe/S ratio = 0.75. (B) EDXS spectrum of the organic matrix loaded with iron phosphates. (C) EDXS spectrum of a sulfur-rich vesicle. Cu peaks are derived from the supporting grid.
Fig 5.
The production of greigite by other Thermococcales.
(A) Transmission electron microscopy image of T. nautili cells mineralized incubated for 168 hours with mineralization medium. Scale bar = 100nm. (B) Transmission electron microscopy image of T. kodakaraensis cells mineralized incubated for 168 hours with mineralization medium. Scale bar = 500nm. The nanocrystals of greigite are indicated by black arrows.