EXOPOLYSACCHARIDE PRODUCTION AND MORPHOLOGY OF AUREOBASIDIUM-PULLULANS GROWN IN CONTINUOUS 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 c ontinuous cultivations. A simple salt medium was used and the feed con centration of ammonium sulphate (0.3-4.2 g l(-1)), the only nitrogen s ource, was varied. Four distinct growth regimes were recognized based on steady-state concentrations of biomass, EPS, glucose, ammonium, nit rogen in the cells (% of dry wt.), and the morphology. At low feed con centrations of ammonium sulphate (0.3 to around 1.1 g l(-1)) the cultu res were N-limited while at high concentrations (>2.8 g l(-1)) the cul tures were glucose-limited. At intermediate concentrations two transit ion regimes were recognized in which both ammonium and glucose were ex hausted and physiological responses to insufficiency in both N and C w ere recognized. Under N limitation the culture consisted of almost equ al amounts of yeast (40%) and mycelium (60%) and the specific EPS prod uction was constant at about 36 mg g(-1) h(-1). When cultures were glu cose-limited the mycelial fraction of the biomass was 85-95% and no EP S was produced.