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B2 Transport and reaction processes in biopellets

(Hempel/Horn)

The central goal of the determination of intra-particulate mass transfer and reaction processes in biopellets is the calculation of product formation via appropriate models.
For this purpose, methods for the experimental determination of mass transfer, substrate conversion and product formation have been developed in the first application period for the filamentous fungus Aspergillus niger AB 1.13 during production of the model product glucoamylase.

The application of microelectrodes made it possible to perform temporally and locally resoluted measurements of oxygen concentrations in biopellets ranging from 250 µm in diameter under defined fluid dynamic conditions. Furthermore, methods for both the quantitative coverage of the model product glycoamylase and its specific mRNA could be successfully established. The results attained via this methods were used for the design of a one-dimensional pellet model for the simulation of growth, mass transfer and substrate consumption. As a necessary simplification the calculations are presently made with a fixed number of pellets of identical size in the bioreactor, which is default for the modelling. The model represents the most important transport and conversion processes in biopellets so that it can be used for further experimental design. There are basically two aspects to further promote in the second application period. On the one hand, the model is to be improved by implementing the particle size distribution of the pellets during the initial stage of cultivation and the local biomass distribution. The metrological support of the model refinement with regard to pellet size distribution is achieved by a very close connection to the sub-project B3 (Hempel/Krull), where these data are collected. It is to be assumed that the pellet size distribution has a not negligible impact on conversion.

 

For biomass density allocation and registration of inhomogeneities in the pellet, confocal laser scanning microscopy (CLSM) is to be increasingly worked with. Therefore, the further development of the microtome technique (sectioning the pellet) with subsequent staining, detection and image analysis is intended.

On the other side, the method for activity measurement in the pellet through mRNA quantification is to be enhanced during the second funding stage. For this purpose, the aim is the localisation of active regions in the pellet through use of CLSM in combination with gene probes.Moreover, it is planned to use a DNA array technology in the future in order to elucidate the gene expression related to product formation (connection with sub-project B4 (Jahn/Nörtemann/Rinas)). With this technology, the applicants expect more detailed information about the metabolic processes which are active in the different cultivation stages. Again, by means of this information, a more differentiated model representation in terms of reaction processes for product formation is to be derived from. Furthermore, it is intended to optimize the method for the production strain with the target product glycosyl transferase developed in sub-project A1 (Jahn) and the strain developed for the production of antibodies (sub-project A6 (Dübel).

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