Exploration of intrinsic peroxidase-like activity of Acidithiobacillus ferrooxidans spent medium and its application for glutathione detection

Acidithiobacillus ferrooxidans ( At. ferrooxidans ) is a bacterium that has the ability to metabolize iron. It converts Fe 2+ into Fe 3+ during its metabolic cycle. Hence, the At. ferrooxidans spent medium is rich in Fe 3+ . The presence of Fe 3+ contributes to a peroxidase-like activity. Therefore, in this study, an attempt has been made to explore the peroxidase-like activity of the At. ferrooxidans spent medium. It has been observed that the At. ferrooxidans spent medium oxidized 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H 2 O 2 ). The effect of various process parameters on the peroxidase-like activity has been studied. Optimum peroxidase-like activity is achieved using 5 µl of the spent medium, 0.3 mM TMB concentration, 4 mM H 2 O 2 concentration, 4.2 pH, and 40 °C temperature. The peroxidase-like activity of the At. ferrooxidans spent medium has been used to develop a colorimetric assay for detection of glutathione (GSH). GSH inhibits the peroxidase-like activity of the At. ferrooxidans spent medium in a concentration range of 0–1 mM. The limit of detection (LOD) of GSH, obtained using the calibration plot is 0.69 mM. The developed assay is selective toward GSH, as the presence of amino acids, metals, and sugars have shown a negligible effect on the GSH sensing ability.