Figure 1.
Tumbling and running modes associated with Escherichia coli and Salmonella typhimurium.
CW rotation results in a random re-orientation for the bacterium, but CCW rotation of flagellar motors produces an approximately straight-line motion.
Figure 2.
Differences between metabolism-dependent, metabolism-independent and metabolism-based chemotaxis.
Arrows indicate only short-term dynamical influence between processes.
Figure 3.
Conceptualization of a minimal metabolism.
An exergonic reaction () is coupled to an endergonic material transforming reaction (
) such that system components are produced (
) that catalyze those reactions.
Table 1.
Constants.
Table 2.
Differential equations.
Figure 4.
Energy required for a reaction to take place.
Figure 5.
Diagram indicating the minimal metabolic reaction and its coupling to tumbling and running modes of behavior.
Figure 6.
Experiment 1: Chemotaxis towards a gradient of and
.
Plot A is a histogram that indicates the distance of bacteria from the location of highest concentration of and
(
) at the start and end of trials. Data are averaged from 10 runs of 100 bacteria each. Plot B indicates the spatial distribution of the simulated bacteria as time progresses in a typical trial. The concentric circles indicate the center of the Gaussian distribution of resources
and
.
Figure 7.
Diagram indicating metabolic reactions for Experiment 2.
Figure 8.
Experiment 2: Abundance of sufficient resources inhibits chemotaxis to attractants.
In this trial, agents were placed on the same gradients as in Figure 6, but with an additional uniform distribution of alternative metabolizable sources . The presence of these resources clearly inhibits chemotaxis to
and
.
Figure 9.
Experiment 3: Inhibition of a metabolic pathway inhibits chemotaxis only to the relevant resources.
Placed in an environment with two sets of metabolizable resources ( located in the lower-right and
located in the upper-right), the simulated bacteria move from an initial, even-distribution to the areas higher in concentration of either resource-pair. The insertion of
(a chemical that inhibits the metabolism of
) causes the simulated bacteria to cease chemotaxis towards the no-longer metabolizable resources without influencing chemotaxis to the other attractants. Histogram A illustrates average distance to the non-inhibited (
) source. Histogram B shows the distance from the inhibited source (
). As before, data is taken from 10 trials of 100 bacteria each. Plot C illustrates the spatial distribution of simulated bacteria in a typical trial.
Figure 10.
Diagram of the metabolic reactions for Experiment 3.
Figure 11.
Experiment 4: Metabolic inhibitors act as repellents.
In a uniform distribution of resources, simulated bacteria move away from high concentrations of the metabolic inhibitor .
Figure 12.
Diagram of the metabolic reactions for Experiment 4.
Figure 13.
Experiment 5: Sensitivity to history.
The metabolism of the bacteria changes when encountering (located at the left side of the environment), as
is incorporated into the cell, making
metabolizable. The
rich area (concentric circles on right side of plots) is initially insufficient to support production of
, but for agents that have incorporated
into their metabolism,
becomes an attractant. Bacteria with
are shown as
s rather than circles.
Figure 14.
Experiment 6: Metabolism-based behavior does not respond directly to environmental features, but rather to their combined effect upon metabolism.
Here we see simulated bacteria concentrated in the area of the environment where the combined influence of all environmental phenomena allow for a sustainable metabolism.