Antibiotics, organic acids, proteins, and polysaccharide gums are among the numerous microbial products of economic importance produced in submerged culture fermentation. Large-scale industrial fermentations rely on the use of stirred-tank bioreactors equipped with baffles and turbine agitators.' Successful process scale-up is based on the concept of equal mass transfer coefficients in Newtonian fluids.2 Mechanical agitation is popular because of its versatility and effectiveness in mixing contents, disruption of air bubbles, and dispersion of cell aggregates. Fermentation broths of actinomycetes and molds exhibit non-Newtonian flow behavior and frequently require modifications in bioreactor design to maintain efficient transfer of nutrients and oxygen to the mycelial mat.3-6
Thermomonospora fusca strain YX is a filamentous aerobic bacterium indigenous to thermogenic composts. This actinomycete secretes a serine protease when grown on c e l l u l o ~e . ~~~
The purified protease exhibits remarkable chemical and thermal Interest in "YX protease" for industrial applications" prompted an investigation into the feasibility of production scale-up using a turbine-agitated fermentor and comparison with shake cultures.