| Summary: | Abstract Background The natural antioxidants from Chlorella have potent therapeutic implication in several diseases. However, the anti-bacterial activity and their molecular mode of action have not been investigated yet. The present study focussed on the assessment of antioxidant potential as well as free radical scavenging activity such as DPPH, hydroxyl radical, hydrogen peroxide, and superoxide anion radical assay of Chlorella vulgaris Beyerinck [Beijerinck] (BUACC25) isolated from marine habitat. Furthermore, the anti-bacterial activity and their molecular mode of action have been evaluated. Results In the present study, the preliminary phytochemical screening of methanolic algal extract revealed the presence of alkaloids, glycosides, proteins, terpenoids, saponins, coumarin, phenols, and tannins, which was confirmed by in an UV-visible and FT-IR spectroscopy, indicated the distinct spectral peaks. The methanolic algal extract was found to be rich in phenolic content (45 ± 0.06 mg GAE g−1) and flavonoid content (470 ± 0.25 mg of RUE g−1). Furthermore, the methanolic extract was revealed potent antioxidant scavenging activity to scavenge various free radicals with minimum IC50 values of DPPH, hydroxyl, H2O2, superoxide 2.82 ± 0.30, 2.30 ± 0.25, 3.24 ± 0.32, and 3.15 ± 0.02 μg ml−1 respectively. Furthermore, the methanolic extract of C. vulgaris exhibited potent anti-bacterial activity which was evident with the reduction in cfu × 107/ml and % of cell viability. Mechanistically, reduction of SOD, CAT, and GSH activity provoked ROS-mediated cell death after drug treatment. Moreover, in combination with norfloxacin and ciprofloxacin, methanolic extract of C. vulgaris demonstrated enhanced anti-bacterial activity with an evident reduction in cfu/ml and % of cell viability. Conclusion This study advocates that C. vulgaris (BUACC25) has promising antioxidant activity owing to the presence of phenolic and flavonoids evidenced by scavenging of DPPH, hydroxyl, H2O2, and superoxide radicals. In addition to this, it sustained anti-microbial activity against E. coli through modulation of SOD, CAT, and GSH. This study carved a path for uncovering a better therapeutic agent against disease-causing bacterial pathogens.
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