Escherichia coli Cultures in Temperature Gradients

Escherichia coli Cultures in Temperature Gradients Sensing and responding to environmental changes is essential for the survival of all living organisms. Many strategies depend on single cell sensing and direct interaction with the environment. Yet microorganisms live in communities. The continuous interaction among members of a community, as well as their interaction with their surrounding, affects the behavior of individuals. In this work we study the response of bacterial populations to temperature gradients. Our focus is the effects of population density on the mode of response. We show that at low concentration, bacteria directly sense and respond to the temperature gradient as single cells. There, the bacteria are able to accumulate near their favorable temperature (35-37°C). As the concentration increases, bacterial metabolism, which is affected by temperature, changes the chemical composition of the environment and therefore the response of the population. Here the bacterial chemotaxis and aerotaxis compete with their thermal sensing and forces the bacteria to move away from their favorable temperature. When the bacterial concentration increases beyond a critical value, the interaction among the members of the population becomes important. As a result, the bacteria accumulate in a highly dense band and travel together towards lower temperatures. At extremely high concentration, a change in the expression level of the bacterial sensing receptors is observed. This change is correlated to the nutrients availability in their environment.