Cdcl2

Cadmium chloride (CdCl₂), nickel chloride (NiCl₂), and arsenic trioxide (AsO₃) were purchased from Fisher Scientific. Dilutions of heavy metals used in these assays were made using a filter sterilized stock solution diluted in antibiotic free DMEM medium.

Stenotrophomonas maltophilia Oak Ridge strain 02 (ATCC #53510) was purchased from the American Type Culture Collection (Manassas, VA, USA), Enterobacter sp. YSU was described previously [29 (link)] and StrataClone SoloPack Competent Cells and the plasmid, pSC-A-amp/kan, were purchased from Agilent (Santa Clara, CA, USA) as components of the StrataClone PCR (Polymerase Chain Reaction) Cloning Kit. TransforMax™ EC100D™ pir-116 Escherichia coli (E. coli) was purchased from Lucigen (Middleton, WI, USA) [30 (link)].
Lennox LB medium was purchased from Amresco (Solon, OH, USA), and R3A-tris medium was described previously [29 (link)]. When required, LB or R3A-tris medium was supplemented with 100 µg/mL ampicillin (Amresco), 50 µg/mL kanamycin (Amresco) and varying concentrations of HgCl₂, ZnCl₂, CdCl₂, CuSO₄ (Fisher Scientific, Fair Lawn, NJ, USA) and HAuCl₄·3H₂O (Amresco).

All strains used
in this study are listed in Table S1 and
were routinely grown in Lysogeny Broth (LB; 10
g/L tryptone, 5 g/L yeast extract, 5 g/L NaCl) at 37 °C with
aeration (agitation at 180 rpm). Solid media contained 1.5% (wt/vol)
agar. Selective media for B. subtilis contained
chloramphenicol (5 μg/mL) or spectinomycin (100 μg/mL),
while selective media for E. coli contained
ampicillin (100 μg/mL). For luciferase assays, B. subtilis strains were grown in a modified M9 minimal media (MM9). The composition
of MM9 was as follows: 1 mM MgSO₄, 0.3% fructose, 1% casamino
acids, 0.05 mM FeCl₃/0.1 mM citric acid solution, deionized
water and 1× M9 salts (31.7 mM Na₂HPO₄,
17.22 mM K₂HPO₄, 17.11 mM NaCl, 9.34 mM NH₄Cl). For transformations of E. coli DH5α
(see below), SOC medium was used with the following composition: 2%
tryptone, 0.5% yeast extract, 10 mM NaCl, 2.5 mM KCl, 10 mM MgCl₂, 10 mM MgSO₄, and 20 mM glucose. For transformations
of B. subtilis, MNGE medium was used based on
the composition described by Radeck et al.^{31 (link)} Further details about the transformation procedure can be found
below. Metal salts Ag(NO₃), ZnSO₄·7H₂O, Pb(NO₃), and CdCl₂ were obtained
from Fisher Scientific, CuSO₄·7H₂O and
HgCl₂ were obtained from Sigma-Aldrich.