High pullulan biosynthesis from high concentration of glucose by a hyperosmotic resistant, yeast-like fungal strain isolated from a natural comb-honey

A novel, yeast-like fungal strain, Aureobasidium melanogenum TN3-1, that was isolated from natural honey can actively transform 140.0 g/L of glucose into 110.29 +/- 2.17 g/L of pullulan during fermentation, whereas A. melanogenum P16 and TN1-2 converted 140.0 g/L of glucose into only 45.81 +/- 1.7 g/L and 48.7 +/- 2.6 g/L of pullulan, respectively. It was noted that most of the cells in the culture of the strain TN3-1 were arthroconidia, while all of the yeast-like fungal cells of A. melanogenum P16 cultivated under the same conditions were blastoconidia. The cell sizes, cell walls and the number of small vacuoles of A. melanogenum TN3-1 were also much larger, thicker and higher, respectively, than those of A. melanogenum P16. The glycerol, trehalose and glycogen content in the A. melanogenum TN3-1 cells was higher than that of the A. melanogenum P16 and TN1-2 cells.