Comparing the data of the mobility of bacteria E. coli, it can be found that the speed of E. coli motions measured in three different patterns fluctuates little. The speed of E. coli in irregular blocks is within the range of speed measured in free motions in plaza zone. It decreased little when the bacteria are in parallel tracks. However, comparing the routines of E. coli in three patterns as well as the angles, it can be observed that it is becoming difficult for bacteria to move in a more complex track as the irregular-blocks part shows. In addition, both three parts of the E. coli indicates that it is difficult for E. coli cells to make a turn on a large angles, typically, larger than 90℃. Therefore, the movement of E. coli cells in confined channels is indeed affected by the patterns, and different patterns can influence the mobility in different aspects like the speed and the angles.
Comparable analysis of the mobility of another bacteria Ps. fluroscens can be obtained basing on the results as well. The causes to the variations in mobility of two bacteria in observations can be explained not only because of the different structure of patterns, but also the bacteria own behaviors. However, the variations of mobility of E. coli cells concern more about the aspect of patterns, while the changes of that of Ps. Fluroscens are associated more with the bacteria own behavior. As it mentions, narrower channels would result in a smaller speed of E. coli, and more complicated channels with different turning points would influence the routines of E. coli and even the marching process consequently. But the remarkable distinctions of the mobility of each Ps. fluroscens cell should be further explained by the bacteria behavior. During the experiment of Ps. Fluroscens, it can be found that a large proportion of bacteria were kept still or spinning at certain locations for a long time. Moreover, it is observed that the bacteria would be much easier to be jammed at each corner of channel or the turning points of a right angle. This phenomenon is related with the peritrichous flagella of the bacteria, as the flagella may be stuck to the channel or the surface of PDMS, which consequently leads to each individual cell to rotate or to be motionless. As there are a large number of Ps. Fluoroscens become jammed in the PDMS channel, the sample size of moving bacteria are too small, so that the analysis of mobility of Ps. Fluroscens may lack accuracy and ubiquity.
Other factors that may cause inaccurate final results are related with the bacteria physiology and the utilization of the software Image J for data processing. Both the E. coli and Ps. Fluroscens have the cell division process during the motions in micro channels, and it slowed down the march of some bacteria. The proper reason for this may be the surface area were growing larger because of the cell division which it is easier for the bacteria to be stuck to the wall channel, and also cell division will charge more energy of bacteria.In addition, the Ps. Fluroscens are may bleach to colorless when they are exposed to the UV lights for a very long time as Figure 1 and 2 indicates. This will result in the great difficulties in observing and recording the bacteria, and errors therefore may be generated in the analysis of the motions of Ps. Fluroscens. There are some errors created during the data analysis with image J, for example, the errors in tracking the trajectories of bacteria manually, and the time measurement. Apart from that, as it has been mentioned previously, errors of measurement are existed since the bacteria may go deeper in the channels instead of going straight forward.
Figure 1 Bacteria initial states
Figure 2 Bacteria bleach after exposing to the UV light for a long time
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