Analysis of pellet formation of Aspergillus niger based on shear stress

Morphology has a crucial effect on productivity and the supply of substrate for cultures of filamentous fungi. However, cultivation parameters leading to the desired morphology are often chosen empirically as the mechanisms governing the processes involved are usually unknown. For coagulating microorganisms like Aspergillus niger the morphological development is considered to start with the aggregation of conidia right after inoculation. To elucidate the mechanism of this process, kinetic studies were carried out using an in-line particle size analyzer. Based on the data obtained from these experiments a model for conidial aggregation is proposed in this article. It consists of two separate aggregation steps. The first one takes place immediately after inoculation, but only leads to a small decrease of total particle concentration. Most suspended conidia aggregate after a second aggregation step triggered by germination and hyphal growth. Aggregation velocity of this second phase is linearly dependent on the particle growth rate. B 2004 Wiley Periodicals, Inc.

Section: Strain and Mediamentioning

confidence: 99%

Kinetic studies on the aggregation of Aspergillus niger conidia

Grimm

Kelly

Hengstler

et al. 2004

“…Oil fermentations show qualitative differences between shake flasks and stirred tanks (Choi et al, 1996;Ho et al, 1990;Ju et al, 1991). Studies on the morphology of filamentous microorganisms have resulted in considerable differences in pellet size between shake flasks and stirred tank reactors (Fujita et al, 1994;Kishimoto and Sawada, 1997) or between shake flasks experiments conducted under different operating conditions (Bushell et al, 1997;Galindo et al, 2004;Katzer et al, 2001;Yang and Liau, 1998). Consequently, process productivity is influenced by mass transfer limitations and the broth viscosity (Olsvik and Kristiansen, 1994).…”

Section: Introductionmentioning

confidence: 96%

Hydromechanical stress in shake flasks: Correlation for the maximum local energy dissipation rate

Peter

Suzuki

Büchs

2006

Shake flasks are widely used in biotechnological process research. Bioprocesses for which hydromechanical stress may become the rate controlling parameter include those where oils are applied as carbon sources, biotransformation of compounds with low solubility in the aqueous phase, or processes employing animal, plant, or filamentous microorganisms. In this study, the maximum local energy dissipation rate as the measure for hydromechanical stress is characterized in shake flasks by measuring the maximum stable drop size. The theoretical basis for the method is that the maximum stable drop diameter in a coalescence inhibited liquid/liquid dispersion is only a function of the maximum local energy dissipation rate and not of the dispersing apparatus. The maximum local energy dissipation rate is obtained by comparing the drop diameters in shake flasks to those in a stirred tank reactor. At the same volumetric power consumption, the maximum energy dissipation rate in shake flasks is about 10 times lower than in stirred tank reactors explaining the common observation of considerable differences in the morphology of hydromechanically sensitive cells between these two reactor types. At the same volumetric power consumption, the maximum local energy dissipation rate in baffled and in unbaffled shake flasks is very similar. A correlation is presented to quantify the maximum local energy dissipation rate in shake flasks as a function of the operating conditions. Non-negligible drop viscosity may be considered by known literature correlations. Further, from dispersion experiments a critical Reynolds number of about 60,000 is proposed for turbulent flow in unbaffled shake flasks.

“…Filamentous fungi were classified into coagulating and non-coagulating types according to their ability to form aggregates. A large number of variables influencing fungal aggregation processes have been published (Amanullah et al, 2001;El-Enshasy et al, 1999;Fujita et al, 1994;Tronchin et al, 1995). Most studies dealing with this issue have drawn conclusions from the morphology of full-grown mycelia.…”

Section: Introductionmentioning

confidence: 96%

Influence of mechanical stress and surface interaction on the aggregation of Aspergillus niger conidia

Grimm

Kelly

Völkerding

et al. 2005

Productivity of fungal cultures is closely linked with their morphologic development. Morphogenesis of coagulating filamentous fungi, like Aspergillus niger, starts with aggregation of conidia, also denominated as spores. Several parameters are presumed to control this event, but little is known about their mode of action. Rational process optimization requires models that mirror the underlying reaction mechanisms. An approach in this regard is suggested and supported by experimental data. Aggregation kinetics was examined for the first 15 h of cultivation under different cultivation conditions. Mechanical stress was considered as well as pH-dependent surface interaction. Deliberations were based on a two-step aggregation mechanism. The first aggregation step is only affected by the pH-value, not by the fluid dynamic conditions in the bioreactor. The second aggregation step, in contrast, depends on the pH-value as well as on agitation and aeration induced power input. For the given experimental set-up, agitation had much more influence than aeration. In addition, hyphal growth rate was determined to be the driving force for the second aggregation step.