Supporting Information

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1 Supporting Information Extracellular Saccharide-Mediated Reduction of Au 3+ to Gold Nanoparticles: New Insights for Heavy Metals Biomineralization on Microbial Surfaces Fuxing Kang,, Xiaolei Qu, Pedro J.J. Alvarez, # and Dongqiang Zhu,* School of Urban and Environmental Sciences, Peking University, Beijing , China College of Resources and Environmental Sciences, Nanjing Agricultural University, Jiangsu , China State Key Laboratory of Pollution Control and Resource Reuse/School of the Environment, Nanjing University, Jiangsu , China # Department of Civil and Environmental Engineering, Rice University, Houston TX 77005, United States Manuscript prepared for Environmental Science & Technology Number of pages: 11 Number of tables: 0 Number of figures: 9 S1

2 Figure S1. Titration curves of residual Ag + by Cl - for the measurement of hemiacetal groups in EPS: blank without any EPS (curve a), EPS form Bacillus subtilis (curve b), EPS from Escherichia coli (curve c), and EPS from Saccharomyces cerevisiae (curve d). The initial concentration of the hemiacetal groups in EPS (32.8 mg L -1 on a dry weight basis) was mmol L -1 for Bacillus subtilis, mmol L -1 for Escherichia coli, and mmol L -1 for Saccharomyces cerevisiae. S2

3 Figure S2. Relationship of the absorbance (OD 524 nm ) and molarity of AuNPs. A: Titration curve of Au 3+ in digested AuNP suspensions as determined by potentiometric-iodometry method. B: Linear correlation between OD 524 nm and the molarity of AuNPs. C: Validation of the potentiometric titration method for Au 3+ analysis by inductively coupled plasma-atomic emission spectrometry (ICP-AES). S3

4 Figure S3. Particle size distributions and average sizes (reported as means ± standard deviations in parentheses) of AuNPs formed in vitro from Au 3+ in the presence of B. subtilis EPS (8 ± 2 nm), S. cerevisiae EPS (8 ± 2 nm), E. coli EPS (7 ± 2 nm), and lipopolysaccharides (8 ± 1 nm) at ph 7.2; in the presence of E. coli EPS at ph 9.0 (8 ± 1 nm), ph 8.0 (8 ± 2 nm), ph 6.0 (7 ± 1 nm), and ph 5.0 (8 ± 1 nm); in the presence of E. coli EPS at low concentration (8.0 mg L -1, 9 ± 1) and high concentration (120 mg L -1, 6 ± 2 nm); in the presence of E. coli cells ( cells L -1, 8 ± 3 nm) at ph 7.2. The reaction mixture was incubated at 30 C for 6 h. The initial concentration of Au 3+ was mmol L -1, and the concentration of EPS or lipopolysaccharides was 32.8 mg L -1 unless otherwise specified. S4

5 Figure S4. Microscopic and spectroscopic analysis of AuNPs formed in vitro from Au 3+ (initially at mmol L -1 ) with aqueous EPS (32.8 mg L 1 ). (A) TEM images of AuNPs formed in aqueous EPS solution. (B) HRTEM lattice-fringe fingerprinting of these AuNPs. The interplanar spacing (0.235 nm) is consistent with the crystal face of element gold. The corresponding characterization by EDS (C), SAED (D), and XRD (E). The signals of Cu and C in panel (C) originated from the carbon-coated copper grid. S5

6 Figure S5. Toxicity test of Au 3+ and AuNPs on E. coli cell growth after 16 h of incubation. Dose-response relationships were compared between Au 3+ and AuNPs formed in vitro from Au 3+ in the presence of aqueous E. coli EPS. The cell densities were initially inoculated at cell ml 1. The optical density (OD) of these suspensions was recorded by the light absorbance at 600 nm wavelength (OD600) using an ultraviolet visible (UV vis) spectrophotometer. After dilution by fold, 50 L of each bacterial suspension was placed on an agar plate with chloride free medium. The cell colonies were counted after incubation at 37 C for 24 h. A calibration curve between the absorbance (OD600) and the cell density was generated. The equation was as follows: Cell density cell ml -1 = 1.91 OD600nm , R 2 = S6

7 Figure S6. Microscopic and spectroscopic analysis of AuNPs formed in vitro from Au 3+ (initially at mmol L -1 ) with aqueous lipopolysaccharides (32.8 mg L 1 ). (A) TEM images of AuNPs formed in aqueous solution of lipopolysaccharides. (B) HRTEM lattice-fringe fingerprinting of these AuNPs. The interplanar spacing (0.235 nm) is consistent with the crystal face of element gold. The corresponding characterization by EDS (C), SAED (D), and XRD (E). The signals of Cu and C in panel (C) originated from the carbon-coated copper grid. S7

8 Figure S7. Comparison of FTIR spectra of E. coli EPS and extracted extracellular lipopolysaccharides before after reaction with Au 3+. A: pristine EPS; B: EPS after reaction with Au 3+ ; C: pristine lipopolysaccharides; D: lipopolysaccharides after reaction with Au 3+. The concentration of EPS or lipopolysaccharides was 32.8 mg L -1, and the concentration of added Au 3+ was mmol L -1. The pristine EPS (A) and lipopolysaccharides (C) show similar spectral characteristics. Based on the previous studies, 1-7 the band at 1650 ± 5 cm -1 is ascribed to the stretching vibration of C=O or C-N, while the band at 1540 ± 5 cm -1 is ascribed to the stretching vibration of C-N and deformation vibration of N-H. The bands at 1451 ± 2 and 1398 cm -1 are ascribed to the carboxylates and carboxylic acids, respectively. The bands between 1080 and 1240 cm -1 are related to the backbone structures associated with saccharides (e.g., C-O-C and RHC(OH)(OR)). The absorption bands less than 1000 cm -1 may be attributed to the fingerprint region of FTIR. After reaction with Au 3+, the absorption bands ( cm -1 ) characteristic of the backbone structures of saccharides (C-O-C and RHC(OH)(OR)) become weaker or disappear, whereas the band of carboxyl groups (1451 ± 2 cm -1 ) becomes much sharper and stronger (Figure S6B and D). This indicates that the hemiacetal groups (RHC(OH)(OR)) in these reducing sugars were oxidized to carboxyl groups (pointed by red arrows) by Au 3+. Additionally, it is worth noting that the band at 1398 cm -1 (carboxylic acids) disappears, probably due to the formation of gold carboxylate salts. S8

9 Figure S8. Concentration of AuNPs (A), formation rate of AuNPs (B), concentration of Au 3+ (C), and concentration of hemiacetal groups (D) as a function of time during the reactions at 30 C for EPS (32.8 mg L -1 on a dry weight basis) originated from three different microbes (Bacillus subtilis, Escherichia coli, and Saccharomyces cerevisiae). The initial concentration of the hemiacetal groups in EPS was mmol L -1 for Bacillus subtilis, mmol L -1 for Escherichia coli, and mmol L -1 for Saccharomyces cerevisiae. The initial concentration of Au 3+ spiked was mmol L -1. The concentration of Au 3+ at a given time was calculated by the difference between the initial concentration of Au 3+ and the concentration of AuNPs produced. The concentration of hemiacetal groups in EPS at a given time was calculated by the difference between the initial concentration of hemiacetal groups determined by Tollens reagent and the reduced concentration of hemiacetal groups (stoichiometrically corresponding to 2/3 of the concentration of AuNPs produced). Both concentration of Au 3+ and concentration of hemiacetal groups gradually decreased as the reaction progressed. S9

10 Figure S9. The hemiacetal-dependent reduction kinetics of Au 3+ (initially at mmol L -1 ) in aqueous extracted E. coli lipopolysaccharides. Pseudo-second-order kinetics plotted as r against [Au 3+ ][R-CHO]; r represents the reaction rate, and [Au 3+ ][R-CHO] is the product of molarities of Au 3+ and R-CHO (hemiacetal groups) in EPS. The reaction rate constant is (4.14 ± 0.02) 10-3 (lipopolysaccharides). The corresponding regression coefficient (R 2 ) is S10

11 References (1) Guibaud, G.; Comte, S.; Bordas, F.; Dupuy, S.; Baudu, M. Comparison of the complexation potential of extracellular polymeric substances (EPS), extracted from activated sludges and produced by pure bacteria strains, for cadmium, lead and nickel. Chemosphere 2005, 59 (5), (2) Guibaud, G.; Tixier, N.; Bouju, A.; Baudu, M. Relation between extracellular polymers composition and its ability to complex Cd, Cu and Pb. Chemosphere 2003, 52 (10), (3) Burie, J.-R.; Boussac, A.; Boullais, C.; Berger, G.; Mattioli, T.; Mioskowski, C.; Nabedryk, E.; Breton, J. FTIR spectroscopy of UV-generated quinone radicals: evidence for an intramolecular hydrogen atom transfer in ubiquinone, naphthoquinone, and plastoquinone. J Phys. Chem. 1995, 99 (12), (4) Abdulla, H. A.; Minor, E. C.; Dias, R. F.; Hatcher, P. G. Changes in the compound classes of dissolved organic matter along an estuarine transect: a study using FTIR and 13 C NMR. Geochim. Cosmochim. Acta 2010, 74 (13), (5) Song, J. Y.; Kim, B. S. Rapid biological synthesis of silver nanoparticles using plant leaf extracts. Bioprocess. Biosyst. Eng. 2009, 32 (1), (6) Comte, S.; Guibaud, G.; Baudu, M. Biosorption properties of extracellular polymeric substances (EPS) resulting from activated sludge according to their type: soluble or bound. Process Biochem. 2006, 41 (4), (7) Kacurakova, M.; Capek, P.; Sasinkova, V.; Wellner, N.; Ebringerova, A. FT-IR study of plant cell wall model compounds: pectic polysaccharides and hemicelluloses. Carbohydr. Polym. 2000, 43 (2), S11