Protein method for investigating mercuric reductase gene expression in aquatic environments

Area of Science:

• Environmental Science
• Biochemistry
• Microbiology

Background:

• Mercury pollution poses significant risks to aquatic ecosystems.
• Assessing the expression of mercuric reductase, a key enzyme in mercury detoxification, is crucial for understanding microbial adaptation.
• Existing methods for measuring enzyme activity can be complex and time-consuming.

Purpose of the Study:

• To develop a novel, sensitive colorimetric assay for quantifying NADPH-dependent, mercuric ion-specific oxidoreductase activity.
• To facilitate the investigation of mercuric reductase gene expression in polluted aquatic environments.
• To provide a reliable tool for assessing mercury resistance in microbial communities.

Main Methods:

• A colorimetric assay was developed using stoichiometric coupling of mercuric ion reduction to a redox chain via NADPH oxidation.
• Residual NADPH was quantified using phenazine methosulfate-catalyzed reduction of methyl thiazolyl tetrazolium, producing a formazan product.
• Spectrophotometric analysis determined formazan concentration, correlating with remaining NADPH and inversely with mercuric reductase activity.

Main Results:

• The assay demonstrated a strong positive correlation (r2 = 0.99) between formazan concentration and residual NADPH.
• Mercuric reductase activity was inversely related to NADPH remaining and formazan produced.
• The assay detected induced mercuric reductase activity from 10(2) CFU and showed up to threefold higher activity in mercury-amended samples.

Conclusions:

• A robust and sensitive colorimetric assay for mercuric reductase activity has been successfully developed.
• The assay is efficient for direct protein extraction from environmental samples, with high recovery rates.
• This method serves as a valuable supplement to molecular techniques for assessing gene expression in mercury-polluted microbial communities.