The Influence of Some Engineering Variables Upon the Morphology of Rhizopus nigricans in a Stirred Tank Bioreactor

P. Žnidaršič-Plazl

Abstract
Morphological characteristics of submerged cultures of steroid-transforming filamentous fungus Rhizopus nigricans were followed in stirred-tank bioreactors at different cultivation conditions. The influence of inoculum concentration and morphology on submerged growth of Rhizopus nigricans in the reactor was investigated. The results indicated the benefit of using inocula below 103 spores mL–1 in order to obtain pelleted growth form and to prevent undesired growth on the broth surface. Furthermore, the effect of energy dissipation rate on the morphology and biomass yield was evaluated by the use of different number and types of impellers at different agitation rates. Our study confirmed the inverse proportional relationship between energy dissipation rate and pellet diameter, which was in correlation with pellet fragmentation at high energy input.

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Keywords
Rhizopus nigricans, fungal morphology, pelleted growth, agitation intensity