Influence of sulphate on the composition and antibacterial and antiviral properties of the exopolysaccharide from Porphyridium cruentum

Aims The influence of two culture media and three different concentrations of sulphate in the medium on the growth of two strains of Porphyridium cruentum and on the production, composition and viscoelastic characteristics, and antimicrobial properties of the sulphated exopolysaccharide (EPS) were studied. Main methods A Bohlin C50 rheometer was used to evaluate the viscosity and elasticity of the EPS solutions. HSV virus, types 1 and 2, Vaccinia virus and Vesicular stomatitis virus were used along with two Gram-negative (Escherichia coli and Salmonella enteritidis) and one Gram-positive (Staphylococcus aureus) bacteria, for testing the antimicrobial activity of EPS. Key-findings The growth of microalgae was higher in NTIP medium and the production of EPS was enhanced by sulphate 21 mM. The protein content of the EPS was enhanced by the addition of sulphate 52 mM and 104 mM; this concentration also induced an increase in sulphate content of the EPS. However, neither the contents of EPS in carbohydrates and uronic acids were affected by the culture medium supplementation in sulphate. In general, the EPS from the Spanish strain presented a higher antiviral activity than the EPS from the Israeli strain. All EPS extracts revealed a strong activity against V. stomatitis virus, higher than the activity of all chemical compounds tested. The EPS from the Israeli strain also presented antibacterial activity against S. enteritidis. Significance Enrichment of the culture medium with sulphate improved protein and sulphate content of EPS. EPS extracts presented a relevant activity against V. stomatitis virus and S. enteritidis bacterium.