The influence of mechanical forces on the morphology and penicillin production of Penicillium chrysogenum

The influence of mechanical forces resulting from the rotation of (multiple) turbine impellers on the morphology and penicillin production of Penicillium chrysogenum Panlabs P-1 was investigated in batch fermentations using semi-defined media. Experiments were carried out at three different scales of fermentation, 5 dm³,100 dm³ and 1000 dm³ working volume, with the impeller tip speed ranging from 2.5 to 6.3 m/s. Throughout all fermentations, the dissolved oxygen concentration never fell below the critical value for maximum penicillin production. Morphological measurements using image analysis showed that the mean main hyphal length and mean hyphal growth unit increased during the rapid growth period and then decreased to a relatively constant value dependent on the agitation intensity. The specific rate of penicillin production (q _pen)and the average main hyphal length during the linear penicillin production phase were lower at high agitation speed, which promoted more rapid mycelial fragmentation and a higher branching frequency. Comparison of the results from the three scales showed that impeller tip speed is a poor scale up parameter whereas a term based on mycelial circulation through the zone of high energy dissipation fitted the data well.List of Symbols C.E.R. mmol/(dm³h) Carbon dioxide evolution rate - D m Impeller diameter - D.O.T. % air saturation Dissolved oxygen tension - L _e m Mean effective length or main hyphal length - O.U.R. mmol/(dm³h) Oxygen uptake rate - P W Total power dissipation - q _pen units/(mg dry cell weight h) rate Specific penicillin production - R.Q. Respiratory quotient - 1/t _cs^–1 Circulation frequency