Homogeneous batch cultures of Aspergillus oryzae by elimination of wall growth in the Variomixing bioreactor

Abstract

A novel principle for mixing and aeration in stirred bioreactors, named Variomixing, was developed. Four baffles are rotated intermittently at a rotational speed slower or similar to the speed of a centrally placed axial flow impeller. Rotational speeds of the baffles and impeller of 5-10 and 500-600 rpm, respectively, results in the highly turbulent flow regime characteristic of conventional bioreactors with high mixing and mass transfer capacities. Stagnant zones around crevices and crannies in which wall growth may commence are avoided since the baffles are never completely at rest. Increasing the rotational speed of the baffles (5 s every 5 min), so that it follows the speed of the impeller (500-600 rpm), cancels the effect of the baffles and a deep vortex and high peripheral liquid flow rates at the reactor wall develop. The vortex ensures that also the head-space of the reactor wall is flushed and any deposits removed. The filamentous fungus Aspergillus oryzae has been grown in batch cultures in the Variomixing bioreactor. Compared to conventional laboratory-scale bioreactors, in which more than 30% of all biomass was found attached to walls, less than 2% of the total A. oryzae biomass was found on the walls in the Variomixing bioreactor.

Transcriptomic comparison of Aspergillus niger growing on two different sugars reveals coordinated regulation of the secretory pathway

“…Carbon-limited chemostat cultures were performed in a Variomixing Bioreactor [ 41 ]. This bioreactor was designed especially for cultivation of filamentous microorganisms, which have a tendency to adhere to and grow on surfaces.…”

Glucose uptake and growth of glucose-limited chemostat cultures of Aspergillus niger and a disruptant lacking MstA, a high-affinity glucose transporter

“…In the filamentous fungus Aspergillus oryzae, K s for glucose is 30 mM during glucose-limited growth in chemostat culture (Carlsen et al, 1996). In contrast, Larsen et al (2004) reported a K s for glucose of 19 mM during growth of A. oryzae in batch cultures. K s values determined for growth in both batch and chemostat cultures depend on substrate uptake, metabolism and growth.…”

“…A stirred tank reactor, the 'Variomixing' bioreactor (Larsen et al, 2004), designed especially for cultivation of filamentous fungi, was used for chemostat cultivation. This bioreactor has unique features, which reduce attachment of biomass to bioreactor surfaces and concomitant wall growth.…”

Characterization of Nerolidol Biotransformation Based on Indirect On-Line Estimation of Biomass Concentration and Physiological State in Batch Cultures of Aspergillus niger

“…Accurate measurements of titrant addition, required to maintain constant pH in bioreactors where cell metabolism causes pH changes, have been used to monitor growth and physiological states of microbial cultures (17–23). Despite its simplicity and general applicability, this inherent information in pH control has not been used to obtain detailed information about the kinetics of growth and metabolism in microbial cultures during biotransformation.…”