Isolation, Purification and Characterisation of a D-galactose and N-acetyl-D-galactosamine Specific Lectin from Marine Sponge Fasciospongia cavernosa

Background: Marine sponges, belonging to the phylum Porifera, are gaining more attention by researchers and industrial sectors from all over the world due to their ability to produce a variety of bioactive secondary metabolites that have many applications including drug discovery. Marine sponges are a promising source of bioactive lectins, which are structurally diverse, many of them in the form of glycoproteins. Objective: To purify and characterize lectin from a marine sponge Fasciospongia cavernosa and to study its antibacterial activity. Method: Lectin from a marine sponge Fasciospongia cavernosa was purified by guar gum affinity chromatography and checked for its biophysical and antibacterial properties. The lectin was subjected to evaluation for inhibition of microbial growth against bacteria by aggregation test. The activity of FCL against the biofilms formed by P. aeruginosa was also carried out. Biofilm is defined as the undesirable accumulation of microorganisms on artificial surfaces immersed in a common matrix. The effect of FCL on biofilm-forming gram negative bacteria P. aeruginosa was tested by crystal violet assay. Results: This lectin, named FCL, has a molecular weight of 80 KDa approximately, was found to agglutinate human ABO, rat, rabbit and chicken erythrocytes. The hemagglutinating activity of FCL was reduced by demetallisation with E.D.T.A and regained by the addition of Ca2+, Mg2+, Mn2+, Ba2+ and Fe2+, which shows the metal dependency of the lectin. The hemagglutinating activity by the lectin was inhibited by D-galactose and N-acetyl-D-galactosamine. The lectin was stable over a range of pH from 2 to 10.5, and up to a temperature 70°C for 20 min. FCL agglutinated B. subtilis, S. aureus and P. aeruginosa and was able to reduce biofilm mass formed by P. aeruginosa. Thus, the marine sponge F. cavernosa lectin, FCL could be used as an antibacterial agent. FCL significantly reduced the biomass of bacterial biofilm tested. Biofilm mass of P. aeruginosa, K. pneumoniae and E. coli were decreased in a dose dependent manner. Conclusion: A novel lectin was isolated and purified from marine sponge F. cavernosa. FCL, a galactose-binding lectin displayed considerable antimicrobial activity in vitro, particularly against gram-positive bacteria and also exhibited a strong antibiofilm activity. Keywords: Guar gum, affinity chromatography, haemagglutination, antibacterial activity, antibiofilm activity, F. cavernosa.