Team:Humboldt Berlin/Modelling
For the purification of minicells, which are derived from the Salmonella Typhimurium (Salmonella) parental cells, the run-time as well as the g factor are the crucial parameters during centrifugation. While conducting the various experimental trials we noticed that this step was critical in harvesting high yields of minicells and can in fact, potentially replace a filtration step to separate parental cells from minicells.
Therefore, we consider the Stokes equation to investigate the optimal run-time of the centrifuge according to chosen g-factor and filled tube height, which approximate by a cylinder. The calculations are conducted for cylindrical Salmonella and spherical minicells. We hope that our insights may help other groups conducting research on minicells to more easily optimize protocols in their experimental setups. Our result for the optimal run-time of the centrifuge is between 3 and 10 minutes.
We give a probability distribution for the diameter of a cell population consisting of
Salmonella parental cells and minicells. This is log normally distributed. From this, we
determine a probability of obtaining a minicell in the range between 0.4 µm and 0.6 µm.
We then use a binomial distribution to determine the probability of obtaining a given
number of minicells. The number of minicells produced as a statistical mean provides an
information of the cell population required for production of the anti-cancer peptid in
sufficient amounts at the site of action, i.e. at cancer cells that are aimed to be treated
This easy to extend model creates dividing Salmonella cells that generate minicells who possess a size and lifetime.
Thus, this model could be utilized in the future as a platform to answer many exciting
questions in the context of minicell therapy. For instance the question, whether less, but longer living and in size increased cells can
destroy more or less tumor then many smaller ones.
Further and most importantly, these insights will then be observable in the context of time. By working closely with our wet lab team, we present a model that is based on already
established literature and supported by additional experiments (such as proton motive
force measurements) to generate size and lifetime distributions
of minicells. Here, we compare the influence of two different size distributions of minicells on population
and remaining life expectancy over time. To simplify the simulation, we assume that the minicells generated during growth equal the
final distribution after purification. Next, we evaluate the influence of purification on the cell size.
For this, we compare the size distribution of minicells, as they are present in the growing
Salmonella culture, to the purified and filtered counterpart. For simplicity sake the generated data associated with the different size distributions will
be called the filtered dataset and the unfiltered dataset.
Filtration was done with a mesh size of 0.45 µm. While asymmetric division of Salmonella into minicell is the only cross interaction of
Salmonella with the minicells is currently implemented, it was important to us that
this feature can be implemented empathized on if needed.Modelling
Model C
Model P
Size Distribution
Simulation