Difference in chemotaxis of Salmonella cells between serine and aspartic acid

Abstract

We investigated how the chemotactic behaviors of peritrichous bacteria that repeat straight swimming (runs) and directional changes (tumbles) differ depending on the chemical species and concentrations of the attractant. Quantification of the intensity of bacterial chemotaxis will be helpful for the prediction of the bacterial accumulation. We conducted microscopic observation of Salmonella typhimurium cells around a capillary filled with the attractant, L-aspartic acid or L-serine. At the same concentration, cells accumulate more rapidly around L-aspartic acid than L-serine, and the accumulation region around L-aspartic acid is larger than L-serine. Then we estimated the intensity of chemotaxis by comparison with the mathematical model, where characteristic behavior in the run-and-tumble motion of chemotactic bacteria is modeled; the cell decreases the tumble frequency when the cell swims toward the direction where the attractant concentration increases. Observed number density of cells is well approximated with exponentially decaying function of the distance from the capillary tip, which is similar trend to the simulation based on the mathematical model. The intensity of chemotaxis, determined from the slope of the exponential distribution, is almost the same regardless of the chemical species of the attractant or the concentration of L-serine or L-aspartic acid. It can be said that the behavior of a single bacterial cell (probability of suppressing tumble) is almost the same in the region where the cell senses the concentration gradient of the attractant, and that higher concentration of the attractant affects mainly the larger detectable region of the attractant.

Keywords

• peritrichous bacterium
• chemotaxis
• run and tumble
• random walk
• capillary assay