Overlap and differences between the inward and outward electron transfer pathways in Shewanella oneidensis

Area of Science:

• Microbial electrochemistry
• Bacterial electron transport
• Biocatalysis

Background:

• The extracellular electron transport chain in Shewanella oneidensis MR-1 is well-understood for current generation.
• Electron uptake mechanisms in this organism are less characterized, posing challenges for microbial electrosynthesis.
• Understanding electron entry is vital for optimizing biocatalysts and preventing off-target reactions.

Purpose of the Study:

• To elucidate the pathway and key components involved in extracellular electron uptake in Shewanella oneidensis MR-1.
• To identify the roles of specific proteins and molecules in facilitating electron entry into the cell.
• To inform the development of Shewanella oneidensis MR-1 as a biocatalyst for microbial electrosynthesis.

Main Methods:

• Genetic analysis to assess the essentiality of outer and inner membrane proteins for electron uptake.
• Biochemical assays to investigate the role of flavins (endogenous and exogenous) in electron transfer.
• Assessment of hydrogenase involvement in electron uptake and cell viability under cathodic conditions.

Main Results:

• The outer membrane MtrCAB complex is essential for electron uptake, while inner membrane CymA shows partial redundancy.
• Endogenous flavins are critical for electron uptake and cannot be substituted by exogenous flavins.
• Hydrogenases are not directly involved in electron transfer but support cell survival during stationary phase.

Conclusions:

• The inward electron transfer pathway in Shewanella oneidensis MR-1 shares components with the outward pathway but has distinct requirements for flavins.
• MtrCAB and endogenous flavins are key determinants of efficient electron uptake.
• Further research is needed to fully optimize electron uptake pathways for microbial electrosynthesis applications.