Akihiro Okamoto

Extracellular redox-active compounds, flavins and other quinones, have been hypothesized to play a major role in the delivery of electrons from cellular metabolic systems to extracellular insoluble substrates by a diffusion-based shuttling two-electron-transfer mechanism. Here we show that flavin molecules secreted by Shewanella oneidensis MR-1 enhance the ability of its outer-membrane c-type cytochromes (OM c-Cyts) to transport electrons as redox cofactors, but not free-form flavins. Whole-cell

<italic>Geobacter</italic> cells utilize self-secreted riboflavin as a bound-cofactor in outer-membrane <italic>c</italic>-type cytochromes to enhance the rate of bacterial electron transport.

The variety of solid surfaces to and from which microbes can deliver electrons by extracellular electron transport (EET) processes via outer-membrane c-type cytochromes (OM c-Cyts) expands the importance of microbial respiration in natural environments and industrial applications. Here, we demonstrate that the bifurcated EET pathway of OM c-Cyts sustains the diversity of the EET surface in Shewanella oneidensis MR-1 via specific binding with cell-secreted flavin mononucleotide (FMN) and riboflav

The iron-reducing bacterium Shewanella oneidensis MR-1 has a dual directional electronic conduit involving 40 heme redox centers in flavin-binding outer-membrane c-type cytochromes (OM c-Cyts). While the mechanism for electron export from the OM c-Cyts to an anode is well understood, how the redox centers in OM c-Cyts take electrons from a cathode has not been elucidated at the molecular level. Electrochemical analysis of live cells during switching from anodic to cathodic conditions showed that

We determined the three-dimensional structures of aspartate aminotransferase (AspAT) from Escherichia coli and its complex with inhibitor (2-methyl-L-aspartate) at 1.8A resolution. This enzyme reversibly catalyzes the transamination reaction and is a dimer of two identical subunits. Each subunit has 396 amino acid residues and one pyridoxal 5'-phosphate as a cofactor, and is divided into two domains, one large and the other small. Upon binding of the inhibitor, the small domain rotates by 5 degr

Abstract Certain microbes are capable of transporting electrons from the cell interior‐respiratory electron chain to insoluble electron acceptors located outside of the cell, a process referred to as extracellular electron transport (EET). Bacteria capable of EET are currently utilized as “living anode catalysts” in microbial fuel cells. Several EET mechanisms have been proposed, yet they lack molecular‐level consistency. Here, we review our recent work, presenting a “bound‐flavin cofactor” mode

Microbes synthesize cell-associated nanoparticles (NPs) and utilize their physicochemical properties to produce energy under unfavorable metabolic conditions. Iron sulfide (FeS) NPs are ubiquitous and are predominantly biosynthesized by sulfate-reducing bacteria (SRB). However, the biological role of FeS NPs in SRB remains understudied. Now, conductive FeS NPs function is demonstrated as an electron conduit enabling Desulfovibrio vulgaris Hildenborough, an SRB strain, to utilize solid-state elec

The microbial transfer of electrons to extracellularly located solid compounds, termed extracellular electron transport (EET), is critical for microbial electrode catalysis. Although the components of the EET pathway in the outer membrane (OM) have been identified, the role of electron/cation coupling in EET kinetics is poorly understood. We studied the dynamics of proton transport associated with EET in an OM flavocytochrome complex in Shewanella oneidensis MR-1. Using a whole-cell electrochemi

Live electrochemistry: Shewanella is an electrogenic microbe that has a significant content of c-type cytochromes in its outer-cell membrane. By using the specific binding affinity of nitric monoxide, we demonstrate the first electrochemical identification and electron-transfer kinetics of cytochromes under living conditions. The results revealed an unusually efficient respiratory electron-transfer chain at the cell/electrode interfaces. Detailed facts of importance to specialist readers are pub

Microorganisms are known to exhibit extracellular electron transfer (EET) in wide variety of habitats. However, as for human microbiome which significantly impacts our health, the role and importance of EET has not widely investigated. In this study, we enriched and isolated EET-capable bacteria from human gut microbes using electrochemical enrichment method, and examined whether the isolates couple EET with anaerobic respiration or fermentation. Upon the use of energy rich or minimum media (wit

The aspartate aminotransferase gene (AspAT, EC 2.6.1.1) of an extremely thermophilic bacterium, Thermus thermophilus HB8, was cloned and sequenced, and its gene product was overproduced. The purified T. thermophilus AspAT was stable up to about 80 degrees C at neutral pH. T. thermophilus AspAT was strictly specific for acidic amino acid substrates, such as aspartate, glutamate, and the respective keto acids. The gene coding for T. thermophilus AspAT showed that it comprised 1,155 bp with a high