Abstract
Shewanella oneidensis MR-1 can biosynthesize cell-supported Cu-nanoparticles (CuNPs), via the bioreduction of Cu(II)((aq)), with excellent catalytic activity for click chemistry reactions. However, enzymatic mechanisms underpinning Cu(II) bioreduction were unclear. Here, the oxidation of hydrogen as electron donor was essential for Cu(II) bioreduction by S. oneidensis and hydrogenase deletion mutants were used to demonstrate the critical role of the periplasmic [NiFe] hydrogenase, HyaB. Wild type (WT) cultured cells coupled hydrogen oxidation to biosynthesis of Cu(0)/Cu(I)-NPs within the periplasm (identified using XRD and TEM with SAED, EDS, EELS); ΔhyaB mutants did not produce CuNPs. Biosynthesized CuNPs were catalytically active for the cycloaddition of methyl azidoacetate and 1-hexyne, confirming the potential for microbial revalorization of Cu(II)-containing wastewaters, by forming catalytically active nanomaterials. Identifying HyaB, as a key mediator for Cu(II) reduction in S. oneidensis is an important first step towards developing industrial bioprocesses for Cu(II) recovery and CuNP synthesis, offering a template for improvements using engineering biology. Interestingly, c-type cytochromes, critical for reduction of other metals, were unable to fully reduce Cu(II)((aq)) in vivo despite being capable of Cu(II) reduction under in vitro conditions. In fact, Cu inhibited outer membrane cytochrome mediated reduction of Pd(II), and this may impact bioreduction of mixed metal solutions/effluents.