Supporting Information
Elucidating the Genetic Basis for E. coli Defense against
Silver Toxicity Using Mutant Arrays
Zongming Xiu, Yuanyuan Liu, Jacques Mathieu, Jing Wang, Dongqiang Zhu and
Pedro J. J. Alvarez
S1. TEM image of the formed nanoparticles
Figure S1. a) AgNPs were formed inside the EPS; b) HRTEM depicts the lattice-fringe
fingerprinting of the formed AgNPs. The interplanar spacing (0.24 nm) is consistent with the
crystal face of elemental silver.
S2. TEM characterization of bacterial cells under silver stress
Figure S2. Morphology of E. coli cells exposed to AgNO3 (8 mg/L). (a) The cytoplasm of the
wild type E. coli contracted away from the cell envelope. (b) Cell debris without intact cells were
observed in the pgaB culture.
S3. Protein production by ORF clones
Protein produced (OD278nm)
WT/BP sodB
Figure S3. Higher amount of proteins are produced in the ORF clones that over-express specific
genes (wild type with blank plasmid (WT/BP), sodB, recA) than the wild type control (WT), and
these proteins (regardless of the gene that codes them) provide binding sites for Ag+, making
ORF clones more resistant to silver. Asterisks (*) denote significantly higher values than WT
control (p < 0.05).
The protein concentration was measured by the Bradford method 1. Wild type E. coli and
ORF mutants were grown overnight (16h), and diluted with DI water to the same OD600 value
(0.8). Cells were washed and harvested by centrifugation (10,000 rpm) and lysed using B-PER
Bacterial protein extraction reagent (Thermo Scientific) to dissolve proteins. The protein
concentrations were measured using a spectrophotometer (Ultraspec 2100 pro, Amersham
Biosciences Inc. NJ, USA) at OD 278nm.
Bradford M. M. 1976. A rapid and sensitive method for the quantitation of microgram
quantities of protein utilizing the principle of protein-dye binding. Anal Biochem 72(1):