2010f s tem

Bacterial-mineral suspensions in (as described above) were imaged using STEM-EELS to determine the elemental composition and redox state of intracellular precipitates. Aliquots of the bacterial-mineral suspension were pelleted after 24 h and fixed using a BalTec HPM010 high-pressure freezer and freeze substitution using 2% OsO₄, embedded in Spurr’s resin, sectioned to 60 nm and mounted on gold TEM grids10 (link). STEM-EELS images were collected using a JEOL 2010F STEM at 200 kV and a resolution of 0.5 eV to image the O-K edge and the Fe-L_2,3 edges.

The samples were characterized by different analytic techniques. XRD was performed on a Philips X'Pert Pro Super X-ray diffractometer equipped with graphite-monochromatized Cu Ka radiation (λ = 1.54178 Å). Scanning electron microscope (SEM, Zeiss Supra 40) and JEOL 2010F(s) TEM were applied to investigate the size and morphology. The HRTEM images, EELS, SAED, and EDX elemental mappings were taken on JEMARM 200F Atomic Resolution Analytical Microscope with an acceleration voltage of 200 kV. XPS was performed by an X-ray photoelectron spectrometer (ESCALab MKII) with an excitation source of mg Kα radiation (1253.6 eV). ICP data were obtained by an Optima 7300 DV instrument. Ultraviolet photoelectron spectroscopy was carried out at the BL11U beamline of National Synchrotron Radiation Laboratory in Hefei, China. The X-ray absorption spectra of Ni and S K-edges were obtained at the beamline 4B7A station of Beijing Synchrotron Radiation Facility (China).