A Novel Aerobic Mechanism for Reductive Palladium Biomineralization and Recovery by Escherichia coli

Figures & data

Table 1. E. coli strains used to determine biological involvement in the reduction of palladium (II) using formate as the electron donor.

Strain	Genotype	Phenotype	Reference
BL21(DE3)	F2 ompT gal dcm lon hsdSB(rB^− mB^−) λ(DE3 [lacI lacUV5-T7 gene 1 ind1 sam7 nin5])	Wild type strain commonly used for recombinant protein expression.	(Studier and Moffatt 1986)
MC4100	F- ΔlacU169 araD139 rpsL150 relA1 ptsF rbs flbB5301	Parental strain for FTD128 and ΔmoaA.	(Casadaban and Cohen 1979)
BW25113	lacl^q rrbBT14 ΔlacZWJ16 hsdR514 ΔaraBADAH33 ΔrhaBADLD78	Parental strain for JW2682 and JW3865.	(Datsenko and Wanner 2000)
FTD128	As MC4100, with in-frame deletion in the fdhE gene.	FDH-O & FDH-N negative.	(Luke et al. 2008)
JW2682	As BW25113, with in-frame deletion of the hypF gene.	Deficient in all hydrogenases.	(Baba et al. 2006)
JW3865	As BW25113, with in-frame deletion of the fdoG gene.	FDH-O negative.	(Baba et al. 2006)
MC4100 ΔmoaA	As MC4100, disruption of the moaA gene.	Deficient in all molybdoenzymes	This study

Figure 1. (A) Complete reduction of Pd(II) to Pd(0) by an aerobically grown culture of E. coli. Both bottles contain cells resuspended in 20 mM MOPS buffer at pH 7.6, and 1 mM sodium tetrachloropalladate (total volume 25 ml). This image was taken 45 min after the addition of formate to the bottle on the right. (B) Reduction by E. coli MC4100 and by controls showing no abiotic reduction of Pd(II). Controls used were killed (autoclaved) cells and cell-free suspension. Soluble Pd(II) in the supernatant was measured using ICP-MS. ▴ = MC4100; ■ = no cells; ♦ = killed cells.

Figure 2. EXAFS data showing the presence of Pd(II) at 0 and 30 min (bottom two traces), and Pd(0) at 1, 3 and 4 h (ascending series). The top trace is palladium foil.

Figure 3. Pd(II) reduction by six different strains of E. coli, using formate as the electron donor. Soluble Pd(II) in the supernatant was measured using ICP-MS. ♦ = BW25113; □ = JW2682; ▴ = JW3865; Δ = MC4100 ΔmoaA; ■ = MC4100; ◊ = FTD128. Data points for BW25113, JW2682 and JW3865 are mean values of triplicates, with standard error shown.

Figure 4. TEM of thin sections of aerobically grown cells showing extracellular palladium; (A) MC4100, inset BL21; (B) BW25113, inset BL21 (no Pd); (C) FTD128; (D) JW2682; (E) MC4100 ΔmoaA; (F) JW3865. Scale bar (A) = 100 nm; (B)-(F) = 500 nm; insets = 1 μm.

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