Iodate Reduction by Shewanella oneidensis Requires Genes Encoding an Extracellular Dimethylsulfoxide Reductase

Area of Science:

• Environmental microbiology
• Biogeochemistry
• Bioremediation

Background:

• Microbial iodate (IO3-) reduction is vital in marine environments and for remediating radioactive iodine contamination.
• Shewanella oneidensis utilizes a metal reduction pathway for anaerobic IO3- respiration, but its electron transport chain remains uncharacterized.
• Understanding the enzymes involved is critical for developing effective iodine remediation technologies.

Purpose of the Study:

• To identify the terminal iodate reductase and other enzymes in the Shewanella oneidensis IO3- electron transport chain.
• To investigate the roles of extracellular electron conduits (EECs) and DMSO reductase in anaerobic IO3- reduction.

Main Methods:

• Construction and analysis of gene deletion mutants of Shewanella oneidensis, including those deficient in EECs (ΔmtrA, ΔmtrA-ΔmtrDEF, ΔmtrA-ΔdmsEF, ΔmtrA-ΔSO4360) and DMSO reductase (ΔdmsB).
• Measurement of anaerobic IO3- reduction rates using lactate or formate as electron donors in defined minimal medium.
• Examination of wild-type cells grown with tungsten instead of molybdenum to assess cofactor requirements.

Main Results:

• The ΔmtrA mutant showed significantly reduced IO3- reduction with lactate, indicating MtrA's requirement for this electron donor.
• The ΔmtrA-ΔdmsEF mutant exhibited severe deficiency in IO3- reduction with formate, suggesting DmsE's role, while MtrA was not required.
• The DmsAB complex was identified as the extracellular terminal reductase for IO3- with both lactate and formate, demonstrating broad substrate specificity.

Conclusions:

• The extracellular DMSO reductase complex (DmsAB) of Shewanella oneidensis functions as a terminal reductase for iodate.
• This study elucidates key components of the IO3- respiratory pathway in S. oneidensis, identifying DmsAB as a critical enzyme.
• Findings contribute to understanding iodine biogeochemical cycling and inform the development of bioremediation strategies for iodine contamination.