Isolation and Characterization of a Fucoidan Degrading Fungal Strain

다국어 초록 (Multilingual Abstract)

In spite of an increasing interest in fucoidans as biologically active compounds, no convenient commercial sources with fucoidanase activity are yet available. A soil fungal strain that showed confluent growth on a minimal medium containing Miyeokgui fucoidan (MF), prepared from Korean Undaria pinnatifida sporophylls, as the sole carbon source was isolated and identified based on a 28SrDNA sequence analysis as a strain of Coniochaeta velutina, and thus tentatively named Coniochaeta velutina PF-2. A cell-free culture supernatant and intact cells of strain PF-2 were examined for the presence of fucoidanolytic activity. The increase in reducing sugars when adding the intact cell into the reaction mixture containing MF as the enzyme substrate was negligible, suggesting that the intact cell did not contain any fucoidan-degrading activities. The culture supernatant depolymerized MF (2,100 kDa) to one major medium-molecular mass fucose-containing oligosaccharides (MMFO-1), having molecular weight ~ 165.5 kDa. However, supernatant neither released the monomer L-fucose from the fucoidan nor hydrolyzed the chromogenic substrate p-nitrophenyl-α-L-fucoside, indicating that the enzyme may be an endo-acting fucoidanase rather than an α-L-fucosidase. HPAEC-PAD analysis of the TFA-hydrolyzed MMFO-1 demonstrated that the MMFO-1 consists of fucose, galactose, xylose and mannose, 504:413:4:4 respectively (mole ratios). The FT-IR spectra of MF and MMFO-1 showed no significant structural difference except for about 10% reduced level of sulfate esters in MMFO-1. This would appear to be the first report on fucoidanolytic activity by fungal strain Coniochaeta species. Moreover, this enzyme activity may be very useful for structural analyses of fucose-containing polysaccharides and the production of bioactive galactofuco-oligosaccharides.