Antioxidant and Cytotoxic Activities of Exopolysaccharides from Alcaligenes faecalis Species Isolated from the Marine Environment of Mauritius

Extracellular polysaccharides (EPS) of microbial origin are polymers with great potential for research and industrial applications. In this study, a sulphated EPS from Alcaligenes faecalis, previously isolated from Mauritius seawater, was investigated for its antioxidant potential using DPPH (1,1-diphenyl-2-picrylhydrazyl) and ferric reducing capacity assays. The EPS was then further tested for cytotoxicity against five different cell lines namely HepG2, A549, CaSki, HeLa and C33A by incubating them with different concentrations of EPS before assessing cell viability using the MTT assay. In the absence of significant cytotoxic activity, light microscopic observations as well as immunoflurorescent staining were also used to observe any EPS-induced effects on the cells. Finally, the average molecular weight of the polysaccharide was determined by Size-Exclusion Chromatography. The results indicated that the EPS, a 55 KDa polymer, had low ferric reducing capacity but showed up to 70.5% DPPH scavenging activity at the highest EPS concentration (1 mg/ml). In terms of cytotoxicity, HepG2 was the most susceptible among the cell lines, followed by A549, with IC50 values of 128.2 µg/ml and 654.4 µg/ml respectively. Although CaSki, HeLa and C33A were more resistant, microscopic observations showed that the EPS did exert some inhibitory effects on their growth, with C33A showing higher inhibition probably due to the absence of viral proteins as was the case for CaSki and HeLa. These results not only suggest that EPS from A. faecalis have the potential to be considered as antioxidant and cytotoxic compounds but also that they can be further studied for their biotechnological value.