B2 Transport and reaction processes in biopellets
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
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).