Control of Fungal Morphology in Continuous Culture

Abstract

The aim of this project was the development of a system for the
continuous production of fungal spores by the control of mycelial
morphology and the optimisation of environmental factors stimulating
sporulation.

Spores, considered a dormant stage in the life cycle of fungi, have
been shown to contain enzymes unrelated to those required for germination,
but which perform a variety of commercially important metabolic activities.
The production of spores in large numbers as stable enzyme packages
therefore has considerable commercial potential.

Sporulation of Aspergillus niger and Aspergillus ochraceus was induced
by growth restriction using nutrient and environmental limitations.
Citrate supported poor sporulation while ammonium nitrogen inhibited
sporulation at all concentrations. Examination of the pH, temperature,
carbon dioxide and ferrocyanide ion tolerance of both organisms indicated
that no physical factor alone induced sporulation. However, a transient
sporulation phase occurred in response to gradual carbohydrate and to
shock nitrate limitations.

To increase spore productivity, the transient sporulation phases were
induced semi-continuously by cycling nutrient supplies. Continuous
production was then achieved in a two-stage fermentation system.

For these systems to operate successfully, continuous growth of the
fungus during sporulation was essential, and there was no upper limit of
growth rate which prevented sporulation. Spore production occurred at
specific carbohydrate supply rates above the calculated maintenance
requirements for fungal survival, but values could not be calculated
for nitrogen maintenance because growth continued without an external
nitrogen supply.

Both organisms displayed variable and much-simplified sporulation
apparatus, indicating that complex structures were not required in a
submerged environment. Sporulation was controlled by a miltivariate and
delicate interaction between growth rate and the nutritional and
physiochemical environment.

The continuous tower fermenter proved ideal for controlling fungal
morphology and enabled a system for the controlled continuous induction of
sporulation to be developed.

Date of Award	1981
Original language	English