  The chemotactic pathway allows bacteria to respond and adapt to environmental
changes, by tuning the tumbling and running motions that are due to clockwise
and counterclockwise rotations of their flagella. The pathway is tightly
regulated by feedback mechanisms governed by the phosphorylation and
methylation of several proteins. In this paper, we present a detailed
mechanistic model for chemotaxis, that considers all of its transmembrane and
cytoplasmic components, and their mutual interactions. Stochastic simulations
of the dynamics of a pivotal protein, CheYp, are performed by means of tau
leaping algorithm. This approach is then used to investigate the interplay
between the stochastic fluctuations of CheYp amount and the number of cellular
flagella. Our results suggest that the combination of these factors might
represent a relevant component for chemotaxis. Moreover, we study the pathway
under various conditions, such as different methylation levels and ligand
amounts, in order to test its adaptation response. Some issues for future work
are finally discussed.
