A 20 L gas-agitated slurry bubble column bioreactor was used to investigate the effects of nonmechanicallow-intensity agitation on de
velopment of broth rheology and fungal pellet morphology during production oflovastatin by the filamentous fungus
Aspergillus terreus. Fermentations were carried out under elevateddissolved oxygen le
vels (400% of air saturation) at gassing rates that ranged from 0.5 to 1.5 vvm. Variousinitial concentrations of the growth limiting nitrogen source were used to attain different total biomassconcentrations, to observe the effect of this variable on de
velopment of pellets and the rheology of thefermentation broth. The non-Newtonian rheology of the fermentation broth was influenced both by the biomassconcentration and the size of the fungal pellets. The stable pellet diameter ranged from ~2300 to ~2900
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m.Too low turbulence (gassing rate of 0.5 vvm) and low dissolved oxygen le
vels adversely affected lovastatinproduction. The best biomass specific production of lovastatin was attained at high biomass concentrationsunder oxygen-rich conditions that were not excessi
vely turbulent. In fermentation broths with various rheologies,the oxygen-transfer coefficient in the bubble column correlated with the aeration
velocity, biomass concentration,and effective viscosity of the broth. The correlations obtained were significantly different for broths withpelleted growth and those with filamentous growth.