Modelling and optimisation of the bioconversion of plant raw materials in an inhomogeneous environment

The BioInh project has evidenced a bi-stability phenomenon that occurs during the enzyme-catalyzed
bioconversion of cellobiose in a non-homogeneous medium (i.e. the presence of two sustainable
functioning modes with different performance). The originality of the approach consisted in studying
this phenomenon using a mathematical model in a first step, which allowed the characterization of
its precise conditions of existence (which would have been very difficult to achieve empirically). This
result has been published in the proceedings of the CAB international conference (Computer and
Applications in Biotechnology) and presented orally in the same conference. This first study has then
permitted the design and the realization of laboratory experiments.
Concerning the mathematical formalism of the problem, the spatial inhomogeneity, one of the key
points of the project, was chosen to be simply represented as "dead zones" instead of using the
commonly used continuous and explicit space representations. Indeed, the latter would have
required the model to be in the form of partial derivatives, with which the study would have been
very difficult to be realized analytically and would have allowed numerical simulations only.
Unfortunately, the enzyme chosen for the experimental studies displayed a different behaviour than
described in the literature, which prevented the experimental data to be used for the validation of
the model.
This study has also resulted in the design of a control law aiming at driving the system toward the
equilibrium with the highest conversion efficiency. The new law has unfortunately not been able to
be experimentally tested because of lack of time (and has therefore not been the subject of a paper
yet).
The BioInh project, financially supported by Agropolis Fondation, has resulted in closer scientific
relations between IATE and MISTEA Joint Research Units and has permitted to launch new long term
collaborations. Indeed, the present project has put forward the coupling of mathematical modelling
with experiments for the study of a specific object (cellobiose hydrolysis). Beyond the theoretical
study and the experimental results obtained, it is a generic approach for modelling and mathematical
formalization that has developed between the two partners, with a working mode. The foreign
partners have played a determining role: R. Lortie (Montréal), who has initiated the definition of the
project, has proposed original and pertinent orientations that would not have been chosen without
his expertise, thanks to his stays in Montpellier granted by the project. Moreover, a large part of the
experiments has been realized by the post-doc researcher A. Saddoud, from Sfax, relayed by
G. Nogaro at the end of the project.