Fig. 2. Cysteine can facilitate biomineralization and form microbial biohybrids.

(A) Optical density measurements showing that in the absence of Cys, E. coli growth is severely inhibited at Cd²⁺ concentrations >0.1 mM. (B) Optical density measurements showing that in the presence of Cys, E. coli cells can tolerate Cd²⁺ concentrations up to 0.3 mM with little adverse effect on growth. The cysteine concentration is fixed at 1 mM. (C) STEM image indicating the formation of biohybrids with mineralized aggregates. Scale bar, 500 nm. (D) Schematic of the synchrotron-based, 3D x-ray fluorescence tomography experiment. Using a zone plate, a monochromatized x-ray beam is focused on the sample. While the sample is raster-scanned, x-ray fluorescence spectra are recorded, forming 2D elemental maps and 3D reconstructions in tomography mode. Using a quadrant photodiode, differential phase contrast images are generated from transmission signals. (E) Selected slice of the 3D x-ray fluorescence tomography reconstruction showing the presence of both the Cd and S elements within an intact bacterial cell. In each virtual slice, Cd-rich regions are identified when pixel intensity is beyond two times of SD from the mean in each virtual slice. Scale bars, 200 nm. (F) Boxplot showing the correlation between the distributions of Cd and S in 3D reconstruction slices. The data are generated from multiple slices in one 3D x-ray fluorescence tomography (check fig. S6). Boxes bind interquartile range (IQR) divided by the median; whiskers extend 1.5 ± IQR. All data points are plotted (n ≥ 380). A two-tailed unpaired t test is used to determine P values. A₆₀₀, absorbance at 600 nm.