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Respiratory arsenate reductase as a bidirectional enzyme
Christine Richey1, Peter Chovanec, Shelley E Hoeft
1Department of Biological Sciences, Duquesne University, Pittsburgh, PA 15282, USA.
Biochemical and Biophysical Research Communications
|March 17, 2009
Summary
Microbial arsenic metabolism is ancient and widespread. The bacterium Alkalilimnicola ehrlichii uses a reversible arsenate reductase (Arr) enzyme for both arsenite oxidation and arsenate reduction, challenging previous assumptions about arsenic enzymes.
Area of Science:
- Microbiology
- Biochemistry
- Environmental Science
Background:
- Haloalkaliphilic bacteria can grow using anaerobic chemolithoautotrophy.
- Arsenic metabolism is a key microbial process with ancient origins.
Purpose of the Study:
- To investigate the mechanism of arsenite oxidation in Alkalilimnicola ehrlichii.
- To determine the enzymatic activity of putative respiratory arsenate reductase (Arr) in A. ehrlichii.
- To explore the reversibility and physiological role of Arr in microbial arsenic metabolism.
Main Methods:
- Genomic analysis of A. ehrlichii to identify genes involved in arsenic metabolism.
- Biochemical assays to determine the enzymatic activity of expressed Arr homologs.
- Comparative analysis of Arr enzymes from different bacterial species.
Main Results:
- A. ehrlichii lacks a conventional arsenite oxidase but possesses two Arr operons.
- One Arr homolog is expressed and exhibits both arsenite oxidase and arsenate reductase activity.
- Arr enzymes from A. oremlandii and Shewanella sp. strain ANA-3 are also biochemically reversible.
Conclusions:
- Respiratory arsenate reductase (Arr) is a versatile enzyme capable of both oxidation and reduction.
- The physiological role of Arr depends on cellular context, including electron potentials and electron transfer chains.
- Microbial arsenic metabolism is ancient, ubiquitous, and highly adaptable.
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