Electrons selective uptake of a metal-reducing bacterium Shewanella oneidensis MR-1 from ferrocyanide

Abstract

The extracellular electron transfer of Shewanella oneidensis MR-1 (MR-1) has been extensively studied due to the importance of the biosensors and energy applications of bioelectrochemical systems. However, the oxidation of metal compounds by MR-1, which represents the inward extracellular electron transfer from extracellular electron donors into the microbe, is barely understood. In this study, MR-1 immobilized on an electrode electrocatalyzes the oxidation of [Fe(CN) 6] 4to [Fe(CN)6] 3efficiently and selectively. The selectivity depends on midpoint potential and overall charge(s) of redox molecules. Among 12 investigated redox molecules, the negatively charged molecules with high midpoint potentials, i.e., [Ru(CN)6] 4and [Fe(CN)6] 4-, show strong electrocatalysis. Neither reference bacteria (Escherichia coli K-12 nor Streptococcus mutans) electrocatalyze the oxidation of [Fe(CN)6] 4-. The electrocatalysis decays when MR-1 is covered with palladium nanoparticles presumptively involved with cytochromes c. However, cytochromes c MtrC and OmcA on MR-1 do not play an essential role in this process. The results support a model that [Fe(CN)6] 4donor electrons to MR-1 by interacting with undiscovered active sites and the electrons are subsequently transferred to the electrode through the mediating effect of [Fe(CN)6] 4-/3-. The selective electron uptake by MR-1 provides valuable insights into the fundamental insights of the applications of bioelectrochemical systems and the detection of specific redox molecules.

Effect of Copper and Phosphate on the Biosynthesis of Palladium Nanoparticles by Shewanella oneidensis MR‐1

“…All NPs of S/CuPdÀ NaCl_C are associated with the cells (Figure 4A and B), contrasting the separated NPs from cells observed in S/CuPdÀ M9_C (Figure 2A and B). The large NPs resemble the ones observed on the MR-1 cells incubated in 0.08 mM Pd(II) for 1 h. [15] Note that the medium for S/ CuPdÀ NaCl_C contains 0.20 mM Pd(II) and the culture time is 24 h. Cu(II) in the medium therefore interferes with the MR-1 metabolism. The large NPs probably form on active sites excluded from the Cu(II) inhibition or before the inhibition took effect.…”

“…The great majority of the cells are entirely encapsulated with PdNPs, forming a thick and rough coating. This coating contrasts with the sparse coating on MR-1 cells incubated in as high as 0.80 mM of Pd(II) for 1 h. [15] As noted, Pd(II) recovery by MR-1 is therefore a rapid process, but one hour is not enough to allow the complete formation of PdNPs on the cellular surface under the current experimental conditions. Some cells are free of PdNPs coating, as indicated by the red arrow in Figure 3B.…”

“…[15] The cellular surface is smooth compared with the counterpart incubated in medium without Cu(II). [15] Pd and Cu signals were both detected in the sample with a comparable amount of cells and extracellular NPs (Site #1) confirmed by EDS mapping, and the former is much stronger than the latter ( Figure S3). The elemental content associated with cells and NPs, i. e., C, N, O, P, S, Pd, and Cu, was determined.…”

“…The culture and collection of S. oneidensis MR-1 (MR-1) were similar as reported, with some modifications. [15] In brief, MR-1 suspension (1.0 mL) from 4°C fridge was added into 100 mL LB. The medium was cultured in a temperature-controlled incubator (30°C, 100 rpm) for 22 h. The cells were collected by centrifugation, followed by washing twice with 0.9 % w/w NaCl aqueous solution.…”

“…The adaptability allows microbes to adapt to different environments. In another recent study, Zhang and associates discovered that Shewanella oneidensis MR‐1 (MR‐1) immobilized on electrodes can accept electrons from six different specific redox molecules including [Fe(CN) 6 ] 4−/3− and shows asymmetric voltammetry with enhanced anodic and lowered cathodic peak current [15] . No similar voltammetry of other bacteria under the same experimental conditions is known [15,16] .…”