Observation of the mobility of bacteria

The second part of the project is observing the mobility of bacteria in microfluidic structures. We practiced this in the bioelectronics laboratory on Feb 3rd, 2012 with Dr. Andrew Libberton.
Two kinds of bacteria which are called E.coli and Pseudomonas fluorescens were used to be researched. Escherichia coli which is gram-negative and rod-shaped is often found in the lower intestine of warm-blooded organisms (Figure 1). Pseudomonas fluoresces is also a gram-negative and rod-shaped bacteria. They have multiple flagella and can be in the soil and in water (Figure 2).

Figure1.E.coli

Figure2. Pseudomonas fluorescens

Since the PDMS has been produced, the next step is to put the bacteria into the channels on the PDMS. Seen from our eyes, the shape of the channel is just a stripe (Figure 3). However, seen from microscope, there are several different kinds of patterns. Using the pipette to collect the bacteria and put them on both sides of the channel uniformly (Figure 4). When collecting the bacteria, the experimenter should keep the cover of the bacteria container closed so as to protect them from contamination. Lid the container of the PDMS and paste the cover with PARAFILM (Figure 5).

Figure 3 PDMS container

Figure 4 Pipette

Figure 5 PARAFILM

The mobility of the bacteria should be observed in the relatively dark room. Camera was used to record the image which is observed by the microscope. The temperature for the operation is minus 75 ℃. A kind of oil can be used to lubricate the lens of the microscope and the glass for better observation.

There are several patterns for recording the movement of the bacteria. Firstly, we observed the mobility of the bacteria in the plaza-like space without channels and recorded whether the most of them went into channels or just move in the space. Secondly, we saw the bacteria swim in the stripe structure. Some of them just went straight quickly through the channel. Some of them swam a few micrometres and went back. The third pattern has several channels and these channels were divided by the different kinds of polygon. We wanted to know which channel the bacteria like to move and what angle the bacteria tend to turn. The fourth pattern is diamond structure with several squares inside it so that bacteria have so many choices or channels to swim from one block to another. Other patterns such as comb structure, small maze structure or a structure like a duck were all used in the experiment to record the various kinds of movement of the bacteria.

All videos of the mobility of the bacteria have been downloaded and they will be the vital materials for us to analyse the characteristic of the movement with software Image J in the next week.

Thanks to the Dr. Andrew Libberton and good luck to us.

                                                                                                           Wrote on 05/02/2012