Exopolysaccharide production and morphology of Aureobasidium pullulans grown in continous cultivation with varying ammonium-glucose ratio in the growth medium.

The influence of the ammonium-glucose ratio on exopolysaccharide (EPS) production and morphology of Aureobasidium pullulans was studied in continuous cultivations. A simple salt medium was used and the feed concentration of ammonium sulphate (0.3-4.2 g l-1), the only nitrogen source, was varied. Four distinct growth regimes were recognized based on steady-state concentrations of biomass, EPS, glucose, ammonium, nitrogen in the cells (% of dry wt.), and the morphology. At low feed concentrations of ammonium sulphate (0.3 to around 1.1 g l^-1) the cultures were N-limited while at high concentrations (>2.8 g l^-1) the cultures were glucose-limited. At intermediate concentrations two transition regimes were recognized in which both ammonium and glucose were exhausted and physiological responses to insufficiency in both N and C were recognized. Under N limitation the culture consisted of almost equal amounts of yeast (40%) and mycelium (60%) and the specific EPS production was constant at about 36 mg g^-1 h^-1. When cultures were glucose-limited the mycelial fraction of the biomass was 85-95% and no EPS was produced.

The influence of the ammonium-glucose ratio on exopolysaccharide (EPS) production and morphology of Aureobasidium pullulans was studied in continuous cultivations. A simple salt medium was used and the feed concentration of ammonium sulphate (0.3-4.2 g l^-1), the only nitrogen source, was varied. Four distinct growth regimes were recognized based on steady-state concentrations of biomass, EPS, glucose, ammonium, nitrogen in the cells (% of dry wt.), and the morphology. At low feed concentrations of ammonium sulphate (0.3 to around 1.1 g l^-1) the cultures were N-limited while at high concentrations (>2.8 g l^-1) the cultures were glucose-limited. At intermediate concentrations two transition regimes were recognized in which both ammonium and glucose were exhausted and physiological responses to insufficiency in both N and C were recognized. Under N limitation the culture consisted of almost equal amounts of yeast (40%) and mycelium (60%) and the specific EPS production was constant at about 36 mg g^-1 h^-1. When cultures were glucose-limited the mycelial fraction of the biomass was 85-95% and no EPS was produced.