Optimization Of Aspergillus Niger Fermentation Based On Fungal Morphology, Physiological Parameter And Bioreactor Engineering Feature

Filamentous fungi are quite valuable in industrial fermentation application. Benefitting from its perfect mechanism in post-translational modification, they possess a huge advantage in the expression of both endogenous and exogenous proteins. Aspergillus niger is one of the typical filamentous fungi, and also a production strain of critic acid, glucoamylase and so on. Glucoamylase is widely applied to industry for its degradation of polysaccharide into monosaccharide, such as glucose. Therefore, besides its huge yields worldwide, glucoamylase is still short in supply, and has a great demand to make further effort on fermentation process optimization. Morphology is an important issue in filamentous fungi fermentation. This could be a critical parameter during the fermentation process. Different fungi morphology could influence and change the fermentation environment greatly, and what’s more, the control of morphology is also complicated since it is affected by almost every environment parameter.Based on the previous study, a fungi morphology auto-analysis approach and rheology measurement method of high solid-contained broth were established,respectively in this paper. After the set-up of fungi morphology analysis process, the’Active Part Percentage’ which combined the understanding of geometry and the biology was also introduced to build up the relationship between the fungi morphology and physiology. Besides, a new kind of impeller-type spindle based on the standard of Brookfield DV-Ⅱ+viscometer was designed and manufactured. This kind of spindle solved the problem of sedimentation effect of pellets and other solids in the broth during the rheology measurement. Afterwards, the relationship between dry cell weight (DCW) and rheology parameter was established, and this laid basis for the further study on the relationship between morphology parameter and rheology parameter.Single factor influencing glucoamylase production process in a bioreactor was investigated in this paper. Oxygen supply condition and agitation speed was studied at serveral levels separately. As a result, obvious extracellular accumulation of oxalate was observed under oxygen-enriched situation, along with a higher biomass concentration. But no remarkable influence to the Aspergillus niger morphology was observed. On the other hand, a shift in agitation speed could result in a clear influence on both physiology and morphology. Serious oxygen limitation could occurred under a low agitation speed and excessive shear forces was encountered under a high agitation speed. Both of them exerted negative impact on fungi growth and fungi activity.At last, influences of different impeller combination on Aspergillus niger were studied in a50L-Scale bioreactor. WHu impeller exhibited an axial flow character and showed a much better result both in production and productivity compared with a standard RT impeller, esp.60%higher on Yp/E. Under a similar control strategy, a more suitable and uniform distribution of shear intensity provided by WHu was confirmed with the aid of both the EDC function and PIV result. The formation of a proper fungi pellet was benefited from the flow feature of WHu impeller, showing a profound impact in energy usage and overall productivity.