The yeast–mycelial dimorphic Aureobasidium pullulans
var.
pullulans was grown in chemostat culture under zinc-limitation
at
pH values in the range 2–7. Steady state was obtained and the growth
yield with respect to zinc was independent of pH. The
culture grew entirely as yeast, independently of the pH in the pH interval
3–7. The exopolysaccharide (EPS) production from the
yeast cells was highest in the pH range 3–6 with a maximum at pH
4·0.
Only little EPS was produced at pH 7·0 and no EPS was
produced at pH 2·1. At pH 2·1 about 20% of the total biomass
was in
the filamentous growth form and some chlamydospores were
present. A change in the carbon source from glucose to sucrose resulted
in a more than doubling of the steady-state EPS
concentration from 3·1 to 6·9 g l−1.
A simple mass balance on carbon was constructed which could account for
more than 95% of the carbon.