Assessment of Combined Effects of Selenium and Cadmium on Antioxidant Activity of Enzymes Produced by Citrobacter freundii

Abstract

Study’s Novelty/Excerpt This study is novel in demonstrating the differential effects of cadmium (Cd) and selenium (Se) on Citrobacter freundii, specifically highlighting the mitigation of Cd toxicity by Se addition. The research reveals that while Cd concentrations above 40 ppm hinder bacterial growth and significantly reduce protein content, Se addition alleviates these detrimental effects, reducing the protein content decline and antioxidant enzyme activities. This work provides new insights into the interplay between heavy metal toxicity and antioxidant defenses in bacteria, suggesting potential biotechnological applications for managing Cd contamination. Full Abstract In this study, Citrobacter freundii (NRRL B-2643) bacteria were cultured in an LB medium with different cadmium (Cd) concentrations.  To mitigate the deleterious impact of Cd, varying quantities of selenium (Se), renowned for its antioxidative power, were added to the cadmium-containing growth medium.  Bacterial concentration, soluble protein, and activities of antioxidant enzymes (Glutathione peroxidase (GSH-Px), Glutathione reductase (GSH-Red), Superoxide dismutase (SOD), and Catalase (CAT) were determined by spectrophotometer.  No significant microorganism growth was observed at 150 ppm and higher Cd concentrations.  However, the bacterial growth was not affected up to 40 ppm Cd concentration.  Bacteria were grown in media containing 0, 75, 100, and 125 ppm Cd, where the 0-ppm cadmium group served as control.  The protein content of the microorganism grown in the medium containing 75, 100, and 125 ppm Cd decreased about 21, 40, and 62 percent, respectively, compared to the control.  When 3.0 ppm selenium was added to the same growth medium, the percentage decrease in protein amount compared to the control was 12, 25, and 50, respectively.  Compared to the control, an increase in the antioxidant enzyme activities in bacteria grown in cadmium-containing media was observed (p<0.05).  With the addition of 1.0 and 3.0 ppm selenium to cadmium-containing media, a decrease was observed in the activities of antioxidant enzymes.