A Novel Aerobic Mechanism for Reductive Palladium Biomineralization and Recovery byEscherichia coli

Abstract

Aerobically grown E. coli cells reduced Pd(II) via a novel mechanism using formate as the electron donor. This reduction was monitored in real-time using extended X-ray absorption fine structure. Transmission electron microscopy analysis showed that Pd(0) nanoparticles, confirmed by X-ray diffraction, were precipitated outside the cells. The rate of Pd(II) reduction by E. coli mutants deficient in a range of oxidoreductases was measured, suggesting a molybdoprotein-mediated mechanism, distinct from the hydrogenase-mediated Pd(II) reduction previously described for anaerobically grown E. coli cultures. The potential implications for Pd(II) recovery and bioPd catalyst fabrication are discussed.

Shotgun proteomics analysis of nanoparticle-synthesisingDesulfovibrio alaskensisin response to platinum and palladium

“…Evidence that these proteins are required for metal ion reduction includes a report that a mopB mutant is unable to grow with hydrogen or formate as the electron donor (31), and that a rhodanese mutant is also unable to use hydrogen as an electron donor (32). More recently it was shown that molybdoproteins are required for Pd 4+ reduction by E. coli (21).…”

“…They similarly have a role, along with a Fe-containing hydrogenase, in Pd(0) deposition and clustering in both the periplasm (18) and on cellular membranes (19), while more recently have been implicated in having a roll in palladium deposition in Shewanella (20). While important for the anaerobic reduction of palladium by Desulfovibrio sp., they are not required for the aerobic reduction of palladium by E. coli (21). Large gaps remain in our knowledge of the proteins involved in metal ion reduction.…”

Selective hydrogenation using palladium bioinorganic catalyst

“…The precise factors which govern reaction selectivity in a complex system where bio-Pd is made on multiple sites of varying hydrophobicity and/or occlusion require further development, probably involving a synthetic biology approach and it should also be noted that the access of substrate to the intracellular Pd-NPs was not measured nor the extent to which the acetone wash removed membrane components (acetone treatment is a recognised method of permeabilising cells [78]). It should also be noted that catalytic intracellular bio-Pd NPs are produced by aerobically-grown cells of both E. coli [79,80] and Serratia sp. [15] which opens the way to using additional types of waste biomass arising from, for example, recombinant product formation since such cells are grown aerobically to maximise the cell yield.…”

Shotgun proteomic analysis of nanoparticle-synthesizing Desulfovibrio alaskensis in response to platinum and palladium

“…Evidence that these proteins are required for metal ion reduction includes a report that a mopB mutant is unable to grow on hydrogen or formate as the electron donor [36], and that a rhodanese mutant is also unable to use hydrogen as an electron donor [37]; both of these mutations lead to a sensitivity to metal ions, as the mutants can no longer reduce the metals as effectively. More recently, it was also shown that molybdoproteins are required for Pd 4+ reduction by E. coli [22]. Five other proteins encode putative ABC-type transportation proteins, Dde_0155, Dde_0186 and Dde_0258, an efflux pump, Dde_3627, and Dde_1010, which potentially encodes an outer-membrane porin.…”

“…They similarly have a role, along with an Fe-containing hydrogenase, in Pd(0) deposition and clustering in both the periplasm [ 19 ] and on cellular membranes [ 20 ], while more recently they have been implicated in having a role in palladium deposition in Shewanella [ 21 ]. While important for the anaerobic reduction of palladium by Desulfovibrio sp., they are not required for the aerobic reduction of palladium by Escherichia coli [ 22 ]. Large gaps remain in our knowledge of the proteins involved in metal ion reduction.…”