Effects of population density and chemical environment on the behavior ofEscherichia coliin shallow temperature gradients

Abstract

In shallow temperature gradients, changes in temperature that bacteria experience occur over long time scales. Therefore, slow processes such as adaptation, metabolism, chemical secretion and even gene expression become important. Since these are cellular processes, the cell density is an important parameter that affects the bacteria's response. We find that there are four density regimes with distinct behaviors. At low cell density, bacteria do not cause changes in their chemical environment; however, their response to the temperature gradient is strongly influenced by it. In the intermediate cell-density regime, the consumption of nutrients becomes significant and induces a gradient of nutrients opposing the temperature gradient due to higher consumption rate at the high temperature. This causes the bacteria to drift toward low temperature. In the high cell-density regime, interactions among bacteria due to secretion of an attractant lead to a strong local accumulation of bacteria. This together with the gradient of nutrients, resulted from the differential consumption rate, creates a fast propagating pulse of bacterial density. These observations are a result of classical nonlinear population dynamics. At extremely high cell density, a change in the physiological state of the bacteria is observed. The bacteria, at the individual level, become cold seeking. This appears initially as a result of a change in the methylation level of the two most abundant sensing receptors, Tsr and Tar. It is further enforced at an even higher cell density by a change in the expression level of these receptors.

Behaviors and Strategies of Bacterial Navigation in Chemical and Nonchemical Gradients

“…When the sensing channel (i.e. the bacterial signaling machinery which translates temperature stimuli into tumbling bias) does not work (e.g., due to deletion of the receptors), the temperature-dependent swimming speed can still cause the directed cell migration [36]. This is consistent with earlier work [20], [21] and our model where mutant strains lacking all receptors can be described by which leads to as described by Eq.…”

“…Our theory can help explain some recent experiments measuring cellular behaviors in shallow temperature gradients [36], [37]. It was observed that even the mutant bacteria lacking all chemoreceptors are still able to migrate toward high temperature [36], showing that there is an additional channel (other than sensing) in regulating bacterial thermotaxis.…”

“…It was observed that even the mutant bacteria lacking all chemoreceptors are still able to migrate toward high temperature [36], showing that there is an additional channel (other than sensing) in regulating bacterial thermotaxis. When the sensing channel (i.e.…”

Environmental Statistics and Optimal Regulation

“…Microorganisms occupy a diverse range of environmental niches, so that characteristic time scales of environmental change range over many orders of magnitude [12]–[14]. Temporal correlations in environmental structure emerge through day and night cycles, seasons, weather patterns, timescales of host dynamics, and complex physical processes like fluid flow, turbulence, and diffusion [15]–[18].…”

Detecting the survival of E. coli Bacteria in Different Types of Water Using Microwave Technique

“…The graph of temperature (°C) versus concentration (c/c o ) is shown in Figure 1. The study shows that as the temperature increase from 16 to 44°C, the concentration of Ecoli increase from 0 to 2.5 c/c o [12]. In order to determine the rate of survival of E. coli bacteria in water, an antenna with certain specifications was designed to detect and analyzed survival of E. coli in fresh water, and drinking water.…”