Phylogenetics and antibacterial properties of exopolysaccharides from marine bacteria isolated from Mauritius seawater

Abstract

The marine environment harbours diverse bacterial species which can be exploited for the production of valuable compounds such as exopolysaccharides (EPS) which hold promises for biotechnological applications. The coastal waters of Mauritius is a relatively underexplored marine environment and in this study, isolated bacterial species were tested for the production of EPS exhibiting antibacterial properties against human bacterial pathogens from the genera Acinetobacter, Bacillus, Campylobacter, Enterobacter, Enterococcus, Escherichia, Proteus, Pseudomonas, Salmonella, Streptococcus and Staphylococcus. Bacteria were first isolated from seawater samples. Using the disc diffusion method, their EPS were tested for antibacterial effects through two screenings, with each involving a different set of arbitrarily chosen group of pathogens. The microorganisms producing antibacterial EPS were subsequently identified by morphological, biochemical and 16S rRNA-based phylogenetic analyses. Those EPS exhibiting broadest antibacterial activities were eventually characterised by Fourier-transform infrared spectroscopy (FTIR) and thin-layer chromatography (TLC). Eight EPS were found to display antibacterial effects against more than half of the pathogens and the microorganisms producing them were identified as Bacillus, Halomonas, Psychrobacter and Alcaligenes species. However, only two of these EPS were found to be the most active, with their MIC values ranging between 62.5 and 500 μg/ml. FTIR and TLC analyses revealed the presence of carboxyl, hydroxyl and amide as well as sulphate for the EPS, with glucose or fructose being the main sugar. The results suggest that Mauritius seawater can be a source of biotechnologically useful microorganisms, producing EPS having potential as antimicrobial agents. DNA sequence data also suggest possible novel bacterial species.