Introduction:

Studies of Acanthamoeba polyphaga trophozoites have indicated they regulate their locomotory speed when encountering prey bacteria, slowing down and grazing until prey in the middle area is cleared (Gaze et al., 2003). It appears that chemokinesis or thigmotaxis is occurring. This project is a linked project with project 1. Image data sets which were collected in project 1 were used for image analysis.

Aims:

To elucidate the mechanism of locomotory regulation in Acanthamoeba polyphaga by analyzing individual trajectories from time-lapse data sets from assays using Salmonella typhimurium as a chemoattractant.

Methods:

Image data was analysed using MATLAB software with development of some existing code, specifically, the paths of individual amoeba on agar were analysed. Four parameters; velocity, trajectory migration, turning rate, and path curvature were extracted from image data. These data Statistics of these four parameters in different conditions were analysed using MATLAB m-files programmed by me.

Results:

u Orthokinesis? If we look at individual amoeba, our results support the hypothesis that the mechanism of amoebae's movement is by orthokinesis (speed changes). This result is different from previous studies by Schuster et al which suggested that the type of response was chemotaxis rather than chemokinesis.

u Chemotaxis? We could see highly significant differences in velocity among different centre-centre distance between salmonellae and amoebae. This result might support a chemotactic response of amoebae, but we couldn't detect obvious directional movements of amoebae towards salmonellae during experiments and the results we obtained seem to be inconsistent in some cases. Improved experimental design of chamber for the assay and use of higher concentration of bacteria or bacterial products may help detect chemotaxis, to overcome this problem.

u Klinokinesis? In different condition, we could see significant difference in amoeba velocity and path curvature, but not in turning rate. We might be able to say that different conditions didn't make a significant difference or stimulus was not strong enough to cause difference in the turning rate.

u Thigmotaxsis? Our result showed a significant difference in amoebae velocity at the presence of beads. However, we didn't see a significant difference in the presence of salmonellae. This result is not consistent and strong enough to conclude that thigmotaxis is occurring. To overcome this problem, we need to prepare the same concentration of beads and salmonellae and compare velocities on them.