Sunday, April 17, 2011

I like to move it, move it!

Bacteria with typical lophotrichous flagella.
'lopho' means tuft and 'trichous' means hair.

Last class along with the various staining procedures we had a look at how bacterial cells get from points A to B. Not all bacteria are motile; however, those that are have various ways to do so. They bear flagella or cilia, and some of them use neither of these, but rather glide.

The experiment we did in class was pretty simple. We had Pseudomonas sp. and Proteus sp. on indented agar in test tubes. We cleaned some microscope slides and placed a drop of water onto them, then used our sterile stick to pick some of the 'boys' from the agar to mix them in the water on the slide. As this suspension turned relatively homogenous we placed a very thin glass cover onto the microbe solution drop. This was important, so we could use the 100x objective which requires immersion oil.

Swarming of the Proteus miriablis Source.
The Proteus sp. turned out to be exceptionally motile. It has ‘peritrichous’ flagella, meaning there are flagella all around its ‘body’. However, these kinds of whips are capable of forming a bundle. This bunch of flagella moves coordinately and propels the cell in a particular direction. This rapid motility exhibits an amazing phenomenon on a Petri dish. If you place a colony of Proteus onto agar, it will show concentric circles. The reason for this is that the cells on the edge of the colony tend to move faster than those in the middle. These outer guys move rapidly away in all directions from the original colony. After a while they settle down and start dividing. Therefore, their daughter cells become the outer ones, rushing away to form new settlements. This kind of motion is called ‘swarming’.

Typical flagella arrangement types. Source.

Unfortunately, we had no device for recording these motions at the university. Though, I found some intriguing pieces of footage on YouTube which I recommend you watch!

This third one is just to show you what we experienced when we dipped a piece of glass into the immersion oil we use for microscopy. The oil's refractive index is the same as glass' so you are unable to distinguish the two.

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