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#### Difference in chemotaxis of Salmonella cells between serine and aspartic acid

Advance Publications (Coming Soon)

##### 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 <i>Salmonella typhimurium</i> 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

- Paper information
- [Advance Publication] (Proper information for citation will be announced after formal publication)

#### Steady distribution of cells in a one-dimensional biased random walk model of bacterial chemotaxis

Volume 11 (2016) Number 02 SI

- Author :
- Tomonobu GOTOTonau NAKAI

##### ABSTRACT

Most bacteria are motile, moving toward suitable environments for subsistence and reproduction. In isotropic chemical environments, they move randomly, changing direction at regular time intervals. In the presence of chemical gradients, they modulate the frequency of the direction change. Collectively, this modulation constitutes the chemotactic response toward a desirable chemical. This study investigates a one-dimensional discrete biased random walk model based on bacterial chemotaxis; a modified version of the classical random walk model. Each cell in the group moves along a uniformly spaced number line at the rate of one interval per time step. A chemical attractant is placed at the origin of the number line. When a cell has receded from the origin in the previous time step, it changes its direction with a probability of 1/2 in the current time step. On the other hand, when a cell has approached the origin in the previous time step, its direction changes with probability (1－α)/ 2 , where α denotes the intensity of the bias toward the origin. In numerical simulations, the cells establish a steady distribution from the origin. This distribution is expressed using a geometric progression whose common ratio depends on α. We provide an analytical explanation of this distribution, which actually constitutes two steady distributions alternating at odd and even positions. Next, the results of the discrete model are compared with those of the corresponding continuum model, namely, a diffusion-advection equation wherein α determines the advection speed. The theoretical solution of the diffusion-advection equation is an exponential decay function, consistent with the distribution obtained by the discrete model.

- Keywords
- Biased random walk, Discrete model, Bacterial chemotaxis, Collective behavior, Steady distribution, Geometric progression, Diffusion advection equation

- Paper information
- Tomonobu GOTO, Tonau NAKAI, “Steady distribution of cells in a one-dimensional biased random walk model of bacterial chemotaxis”, Journal of Biomechanical Science and Engineering, Vol.11, No.2 (2016), p.15-00587. doi:10.1299/jbse.15-00587. Final Version Released on June 24, 2016, Advance Publication Released on February 29, 2016.

#### Boundary Element Analysis on Transition of Distance and Attitude of a Bacterium near a Rigid Surface

Volume 05 (2010) Number 04

- Author :
- Tomonobu GOTOTonau NAKAIKota AOKI

##### ABSTRACT

Swimming motion of a singly flagellated bacterium close to a rigid surface was numerically investigated. The cell's attitude and its distance from the surface were calculated by integrating the velocity and angular velocity determined by the boundary element analysis at an instant. A diagram indicating the transition of the cell's state that was defined as a couple of the pitch angle and the distance was obtained. Four separated regions exist on the diagram for an average size cell. When the absolute of the pitch angle is bigger than a certain threshold value, the cell monotonically leaves from the surface, or approaches and touches the surface. With a moderate pitch angle, the state for forward motion converges to a point, while the state for backward motion diverges since the state of backward motion conversely follow the same transition path. The observed asymmetry between forward and backward motions is explained according to the diagram.

- Keywords
- Bacteria, Swimming, Motion, Surface, Attitude, Boundary Element Analysis

- Paper information
- Tomonobu GOTO, Tonau NAKAI and Kota AOKI, “Boundary Element Analysis on Transition of Distance and Attitude of a Bacterium near a Rigid Surface”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 4 (2010), pp.329-339 . doi:10.1299/jbse.5.329

#### Speed, Trajectory and Increment in the Number of Cells of Singly Flagellated Bacteria Swimming Close to Boundaries

Volume 04 (2009) Number 01 SI

##### ABSTRACT

The influence of a rigid boundary and a free boundary on the motion of singly flagellated bacteria is experimentally investigated. The speed of backward swimming cells is faster near the rigid or free boundary than in the free space without boundary. It is also found that backward swimming speed is faster than forward near the rigid or free boundary. The trajectory of the cells swimming backward near a rigid or free boundary comprises circular parts, while most of forward swimming cells have straight trajectories. Backward swimming cells tend to gather on a rigid or free boundary rather than forward swimming cells. These asymmetric characteristics between forward and backward motions close to a rigid boundary has been predicted by a fluid dynamic simulation.

- Keywords
- Swimming Speed, Trajectory, Bacterial Motion, Rigid Boundary, Free Boundary, Number of Cells

- Paper information
- Tonau NAKAI, Masayuki KIKUDA, Yuichiro KURODA and Tomonobu GOTO, “Speed, Trajectory and Increment in the Number of Cells of Singly Flagellated Bacteria Swimming Close to Boundaries”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 1 (2009), pp.2-10 . doi:10.1299/jbse.4.2