Pullulan production by an osmotolerant Aureobasidium pullulans RBF-4A3 isolated from flowers of Caesulia axillaris

Phenotypic and molecular characterization of five yeast-like fungal isolates from flowers of wild plants showed that they are related to Aureobasidium pullulans. Compared to other isolates, an osmotolerant and non-pigmented isolate A. pullulans RBF-4A3 produced 26.35 g l−1 of melanin-free exopolysaccharide (EPS) in 96 h at 30 °C in 5% glucose containing medium. At higher concentrations of glucose (7.5–25% (w/v)), the EPS produced by this organism increased from 34.68 to 66.79 g l−1 up to 15% (w/v) glucose, with a productivity of 16.69 g l−1 per day. Beyond 15% (w/v) glucose concentration, the EPS production decreased gradually to 43.29 g l−1 at 25% (w/v) glucose. Fourier-transform infrared (FTIR) spectroscopy confirmed that chemical structures of the exopolysaccharide produced by A. pullulans RBF-4A3 and standard pullulan were identical. This is the first report of pullulan production at 15% (w/v) concentration of glucose by an osmotolerant strain of A. pullulans.