ANTIMICROBIAL COMPOUNDS AND EXTRACELLULAR POLYSACCHARIDES

Antimicrobial compounds and exopolysaccharides (EPSs) can be produced by using Sponge-associated Bacteria. Bacteria associated with the marine sponge Haliclona sp. from the coastal region of Waigeo Island were screened for antimicrobial activities using the agar-overlay method.

There were 125 bacterial isolates recovered and were subjected to antimicrobial screening for antibiotic production against five test bacterial strains, viz., Bacillus subtilis, Escherichia coli, Staphylococcus aureus, Enteropathogenic Escherichia coli (EPEC), Pseudomonas aeruginosa and two fungal pathogen, viz., Candida albicans and Candida tropicalis. A total of 39 (31%) bacterial strains were found to be antimicrobial producers; however, 15 (38%) of these active strains were eliminated based on the results of Hemolytic Test. The remaining 24 isolates were further analyzed by amplified ribosomal DNA restriction analysis (ARDRA) to assess their genetic diversity and results obtained revealed eight phylotypes.

These compounds were separated and purified, and their structures were investigated. The activity of the antimicrobial compounds and the rheological properties of the EPSs were also studied. Thirteen Lactobacillus and five Pediococcus strains were shown to produce a low-molecularmass antimicrobial compound, which was separated and purified by chromatographic methods. Identification by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry showed that the antimicrobial compound was 2-pyrrolidone-5-carboxylic acid (PCA), also known as pyroglutamic acid. The technique of anion exchange chromatography developed in this study was essential for effective separation of PCA from lactic acid, facilitating the identification of PCA.

Further studies on the EPSs produced by Finnish fermented milk ‘viili’ strains showed that the
slime-forming Lactococcus lactis ssp. cremoris strains (ARH53, ARH74, ARH84, ARH87, B30)
produced EPSs of relatively high viscosities. These EPSs differed in viscosity in aqueous solutions, and
the viscosity was temperature, pH and salt dependent. Addition of EPS to skim milk significantly
increased the viscosity, and gelation occurred at 40 °C. 1H NMR spectroscopy showed that the EPSs
had a similar or probably identical structure to the one previously reported.