Mrs C. (Caroline) Tolla

Adress: Oceanology Centre of Marseille (COM) Laboratory of Microbiology Geochemistry and Marine Ecology (LMGEM) Campus de Luminy Case 901 13288 MARSEILLE Cedex 09
Phone: 0033-0491829126
Curriculum vitae
Specialization: Mathematical Biology
Project: Heterotrophic bacteria in marine sediments

Dynamical modelling of bacterial communities and their interaction with the organic matter, in marine sediments


The marine sediments are characterised by the coexistence of oxic and anoxic areas where degradation processes are different. The organic matter degradation in these sediments is faster in heterogeneous than in homogeneous environment. This results is obtained from experiments in laboratory where the degradation velocity is measured in oxic (oxygen saturation), anoxic and oscillating conditions (oxic and anoxic mixing). We have developed a model allowing to put in an obvious this result and suggesting some explaining mechanisms.

Aim of study

The aim of this study is to better apprehend the organic matter fate in the sedimentary column, by modelling the mechanisms and velocities of the organic matter transformation/mineralization, dependent on the environmental conditions (i.e. presence or absence of oxygen). More precisely, we set out to improve the usual dynamical models of bacterial communities.


Firstly, a comparative study, between classical models of bacterial dynamic, has been realised through a fit to a set of data concerning the Pseudomonas nautica strain. We have constructed a mechanistic model of bacterial dynamic based on the DEB theory allowing a description of biological behaviour in order to study various environmental conditions.

More precisely, this model was improved thanks to a new mathematical formulation allowing the description of the electron acceptor inhibition by the presence of another one. Notably, we have studied the inhibition of denitrification process by the presence of oxygen, where some others usual mathematical relations are particular cases. This work leads to a publication, published in Acta Biotheoretica (Talin et al., 2003). On the other hand, we applied this new inhibition formulation to the maintenance process. Indeed, a best description of this last process can take its importance in a spatial and temporal variable environment. A publication is in preparation that we will submit to the Journal of Theoretical Biology (Tolla et al., in prep).

The complete model construction based on the DEB theory:

This really important step consists in constructing a model that will answer to the initial problem. In this case, we want to represent, as better as possible, the bacterial dynamic in variable environmental conditions. This model, based on the DEB theory, describes the dynamic of bacterial communities through the assimilation, growth and maintenance processes of the community at the individual scale. The processes description is at the enzymatic scale, associated to the organic matter degradation in marine environment. One of the advantages of the DEB theory, comparing to the classical bacterial models, is of respecting the conservation mass law. Some simulations have been realised with the Matlab and Octave softwares, in order to analyse the qualitative behaviour of the solutions of model equations.

The new mathematical inhibition formulation:

The new formulation is based on the enzymatic kinetics subjacent to the studied process. A first application was realised for the maintenance process (continuous use of energy necessary for the organism care) which is preferentially realised from mobile and available material than from structural material. This preferential use was redrawn by a new formulation, following on from a mathematical and numerical study. The softwares used are Octave and Matlab concerning the simulations and fitting to a set of data, and Mathematica for the steady state expression.

This is the symposium that concludes my project: