Testing an agent-based model of bacterial cell motility: How nutrient concentration affects speed distribution

TL;DR

This study tests an agent-based model of bacterial motility against experimental data, showing nutrient levels increase energy uptake but do not significantly change bacterial speed, which remains around 40μm/s.

Contribution

The paper evaluates different hypotheses for energy conversion in bacterial motility models and compares predictions with experimental data across nutrient conditions.

Findings

Both energy conversion hypotheses fit experimental data with 5 between 1.67 and 2.0.

Higher nutrient levels increase energy uptake but do not raise bacterial speed.

Most probable bacterial speed remains around 40m/s regardless of nutrient concentration.

Abstract

We revisit a recently proposed agent-based model of active biological motion and compare its predictions with own experimental findings for the speed distribution of bacterial cells, \emph{Salmonella typhimurium}. Agents move according to a stochastic dynamics and use energy stored in an internal depot for metabolism and active motion. We discuss different assumptions of how the conversion from internal to kinetic energy $d(v)$ may depend on the actual speed, to conclude that $d_{2}v^{\xi}$ with either $\xi=2$ or $1<\xi<2$ are promising hypotheses. To test these, we compare the model's prediction with the speed distribution of bacteria which were obtained in media of different nutrient concentration and at different times. We find that both hypotheses are in line with the experimental observations, with $\xi$ between 1.67 and 2.0. Regarding the influence of a higher nutrient concentration, we conclude that the take-up of energy by bacterial cells is indeed increased. But this energy is not used to increase the speed, with 40$\mu$m/s as the most probable value of the speed distribution, but is rather spend on metabolism and growth.