E. coli in Plaza zone and plaza tracks

E. coli cells in plaza zones normally are in random motions with no permanent routines. The trace of bacteria have been tracked and recorded by Image J. Hence, the routines of E. coli cells are visualized, and the speed of their movements can be measured as well. According to the statistics, the swimming speed of E. coli is in the range from 19.15 um/s to 35.39 um/s, and the average speed of E. coli cell in microfluidics are 23.37 um/s. In addition, it is found that a number of E. coli have the tendency to swim until they reach the wall of PDMS, and then the bacteria will continue moving along the planar as the Figure1 and Figure2 showed. This is related with the flagella of the E. coli cells. As Ramia et al. has concluded in the model of hydro-dynamism, the movement of bacteria in aqueous medium can be benefited from the propulsion generated during the process when it is closed to the surface and move along with planar.

Figure 1

Figure 2

The second pattern in study is the parallel track that has been mentioned in previous section. Eight parallel tracks with different width connecting with the plaza zone have been provided to the E. coli cells. The motions of E. coli in this pattern can be divided into three stages, entering the tracks, moving inside the tracks, and exiting the tracks. According to the observation results, the movements of entering the tracks from the plaza zone and exiting the tracks to the plaza zone are similar. The average speed of entering the channels from the plaza is 26.69 um/s, and the average speed of exiting the channels to the plaza is 25.51 um/s. Moreover, when considering the routines of entering the channel, as the Figure 3 has presented, it can be seen that three traces of three E. coli cells entering the channel from the plaza at the same time are generally in a line along with the same orientation that parallel to the channels. There is a little number of E. coli turning a right angle immediately after coming in or out of the channels from or to the plaza.

Figure 3

After bacteria enter the channel, their movements inside the parallel tracks are typically the linear motions along with the wall of channels.The average speeds of eight different channels have been calculated based on the measurements. It can be seen that the speed of E. coli in channel 1 with the largest width is similar to the speed in plaza zone. When the channel width decreases, but is still larger than the size of bacteria, the speed of bacteria has decreased to around 15 um/s. Reasonable explanations to the too small number of velocity may be related with the bacteria behaviors such as the cell division, which will be discussed later. The low velocity of channel eight indicates that the bacteria swim quite slower comparing to those of other channels. This is because the width of channel eight is very close to the size of E. coli cells, so that flagella of E. coli cells are difficult to be entirely stretched to assist the swimming.

                                                                                                   Wrote on 21/02/2012