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Supporting information
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Supporting titles and legends to figures
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Figure S1: Fe K edge XANES spectra across two microtome slices. A. Light optical image
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of a biofilm slice. X-ray S K and Fe Ka fluorescence emission scans (not shown here) and X-
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ray absorption spectra of the series shown in S1C have been collected approximately along
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the horizontal line. Scale bar (200 µm). The cross sections are taken from spot 1 of the
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oxygen profiles (Figure 1A) B. Fe K XANES spectra across a biofilm slice (black solid and
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dashed lines) compared to the spectrum from sample position 1 that fits well with the
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spectrum of jarosite (KFe3(SO4)2(OH)6) (grey line) and, hence stands for complete oxidized
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iron. C. Fe K XANES spectra from a second cross section compared to the spectrum 1 from B
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(grey line). A few other spectra, two from the boundary part of the biofilm and one from the
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inner part are close to the jarosite spectrum (dashed line) and therefore represent an almost
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oxidized state of iron whereas the flanks of the other sample spectra are shifted to lower
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energies (solid black line) compared to the jarosite spectrum. Position 1 and 22 in B, and 2
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and 25 in C represent rim locations.
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Figure S2: Identification of Fe K edge XANES end member spectra of the spectral series
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of two cross sections. The spectrum with the flank shift to the highest energy of the series (a)
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(solid line) matches with the spectrum of jarosite (KFe3(SO4)2(OH)6) (dashed line, b) and is
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hence identified as one of two end member spectra. No match of the spectrum with the flank
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position at the lowest energy of the series (dashed line, c) with any known reference spectrum
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was found. Assuming still spectral fraction of jarosite in spectrum (c), a hypothetical end
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member can be derived when subtracting as much jarosite spectral fraction until the white line
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or flank position (solid line, d) of a typical Fe(II) spectrum (dashed line e) is reached. A
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spectrum of dissolved Fe(II) sulfate has been chosen for comparison because it shows similar
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features as the hypothetical end member. From this, it is assumed that the second Fe species
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originates from Fe(II) absorbed in a relation with sulphate on constituents of the biofilm.
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Figure S3: S K edge XANES spectra across two biofilm slices. Spectra that show dominant
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sulfate (dashed and dash dotted lines) are located at the boundary of the slice but seem to
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occur periodically also across the slice. A. The positions of the sulfate dominant spectra where
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Fe K XANES spectra have been recorded match nearly completely with the ones that show
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the most oxidized Fe (see Figure S1B). B. The positions of the sulfate dominant spectra where
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Fe K XANES spectra have been recorded, match with almost all that show the most oxidized
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Fe: Positions 2, 10, and 25 (see Figure S1C). At position 26 almost a pure sulfate spectrum
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has been recorded (dash dotted line).
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Figure S4: Comparison of three typical S K edge XANES spectra of the biofilm slices.
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They show all four spectral features (a) with reference spectra of selected organic and
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inorganic sulfur containing compounds: jarosite (b), taurine (c), anthraquinone-2-sulfonic acid
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(d), DMSO (dimethyl sulfoxide) (e), poly (1,4-phenylene-sulfide) (f), S-methyl-L-cysteine
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(g), L-methionine (h), L-gluthathione (reduced) (i), L-cysteine (j), elemental sulfur (k), pyrite
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(l).
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Figure S5: The CARD FISH images show the inner part of the upper piece (1 cm from the
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rock surface) of the snottite. A. Archaea (ARCH915, Alexa 546 in red) and
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Thermoplasmatales (TH1187, Alexa 488 in green) show almost the same signal. B. ARMAN
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(ARM 980, Alexa 488 in green) signals correlate partly with the archaeal signals (ARCH915,
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Alexa 546 in red).