Shewanella oneidensis MR-1 as a bacterial platform for electro-biotechnology

Abstract

The genus Shewanella comprises over 70 species of heterotrophic bacteria with versatile respiratory capacities. Some of these bacteria are known to be pathogens of fishes and animals, while many are non-pathogens considered to play important roles in the global carbon cycle. A representative strain is Shewanella oneidensis MR-1 that has been intensively studied for its ability to respire diverse electron acceptors, such as oxygen, nitrate, sulfur compounds, metals, and organics. In addition, studies have been focused on its ability as an electrochemically active bacterium that is capable of discharging electrons to and receiving electrons from electrodes in bioelectrochemical systems (BESs) for balancing intracellular redox states. This ability is expected to be applied to electro-fermentation (EF) for producing value-added chemicals that conventional fermentation technologies are difficult to produce efficiently. Researchers are also attempting to utilize its electrochemical ability for controlling gene expression, for which electro-genetics (EG) has been coined. Here we review fundamental knowledge on this bacterium and discuss future directions of studies on its applications to electro-biotechnology (EB).

Transcriptome Analysis to Identify Crucial Genes for Reinforcing Flavins-Mediated Extracellular Electron Transfer in Shewanella oneidensis

“…EET is a sophisticated network that involves the coordination of multiple intermediates and complex interactions ( Lubner et al, 2017 ; Ikeda et al, 2021 ). Thus, many in-depth targets might also lead to unexpected improvement for the desired phenotype.…”

Towards Application of Electro-Fermentation for the Production of Value-Added Chemicals From Biomass Feedstocks

“…Despite the above-mentioned differences, these EET pathways are conduits of electrons, facilitating electrons transfer in both directions (either from the inside to outside or from the outside to inside). For instance, the EET pathway of Shewanella oneidensis has a shallow gradient of redox potential (it gradually increases from the inside to outside), resulting in relatively high anodic current to high-potential electrodes compared to cathodic current from low-potential electrodes ( Ikeda et al, 2021 ). These observations suggest that EET pathways can be used for controlling intracellular redox states (e.g., redox balances of NAD+/NADH) using extracellular electrodes whose potentials are arbitrarily set in BESs.…”

“…It is however unfortunate that the wild-type strain of S. oneidensis is incapable of glucose utilization ( Hirose et al, 2019a ), while a study has shown that introduction of two genes encoding sugar permease and hexose kinase in Escherichia coli facilitates this bacterium to grow on glucose ( Nakagawa et al, 2015 ). In addition, since it has been known that expression of catabolic enzymes and electron-transport proteins in S. oneidensis is complexly regulated at the transcription level ( Hirose et al, 2018 ), further studies on its regulatory mechanisms would be necessary for EF to efficiently utilize designed catabolic pathways ( Ikeda et al, 2021 ). Another EAB that is genetically accessible is Geobacter sulfurreducens ; the use of this bacterium in BESs is attractive in terms of its high electrochemical activity ( Ueki, 2021 ), while genetic manipulation of this bacterium would be more difficult than S. oneidensis owing to its inability to grow aerobically.…”

Tuning Redox Potential of Anthraquinone-2-Sulfonate (AQS) by Chemical Modification to Facilitate Electron Transfer From Electrodes in Shewanella oneidensis

“…The underlying mechanisms for electron transfer between electrodes and microbes were majorly investigated in a model dissimilatory metal reducing bacterium (DMRB) Shewanella oneidensis MR-1 ( Kracke et al, 2015 ; Kumar et al, 2017 ; Rowe et al, 2018 ). This strain was reported to use a broad spectrum of terminal electron acceptors, such as heavy metal minerals, fumarate, dimethyl sulfoxide, nitrate and thiosulfate ( Ikeda et al, 2021 ). S. oneidensis MR-1 employs several different strategies to capture electrons from the cathode, including cytochromes, nanowires and extracellular ESs ( Tremblay and Zhang, 2015 ).…”