Field of Science


Well, I know things have been a little silent around this blog, and there are a couple of reasons for this. One of them I can't say, and will be clear later, one of them is far too personal for a blog, and the other I feel I can share with any of my loyal readers who might have popped in to look at the cobwebs.

In less than a week, the Lab Rat is getting married:

Picture from House of Mouse - who apparently makes lots of these...

Exciting though blogging is, wedding preparations have unfortunately had to take precedent, and seeing as I'm actually no longer working in a lab (and not regularly exposed to papers) it was quite hard to make time to find as much interested bacterial research as I would like.

I'll be back by the second weekend in April, and ready to start properly blogging again, probably twice weekly posts, and possibly some more exciting information...

And for those interested I'll be keeping the same name, I'll just be Mrs Lab Rat, rather than Miss Lab Rat. Hopefully some day Dr Lab Rat as well!

Signals for Infection

ResearchBlogging.orgNeisseria meningitidis is a bacteria which lives in the throats of around 30% of the human population. In most cases it causes no problems at all and just exists as a normal part of the throat microbial flora. In some patients however it can start to colonise the bloodstream and brain, leading to cases of septicemia and meningitis which are highly dangerous and can be fatal.

The invasion starts with individual bacteria, which adhere to the epithelial cells that cover the inside of the throat. They then start to divide and proliferate to form large aggregated colonies. Within these colonies they are connected to each other, and to the epithelial cells, by protrusions from the bacterial cell surface called pili which are shown below for a wild-type (i.e un-genetically modified) Neisseria meningitidis:
Image taken from the reference below. The arrow points to one of the pili, and the insert shows a close-up of it.

These pili are often modified by the attachment of small molecules to the pili proteins, including the molecule phosphoglycerol (shown on the right for those interested in structure). To test the effects of the addition of phosphoglycerol, the researchers found which gene caused the addition of this molecule onto the pili (the pptB gene), and removed it from the cell. Without the pptB gene there was still the same number of pili around the cell, but they were not clumping together as much. Instead of the thick fibres seen in the wild type above (caused by large bundles of pili) only little stringy fibres were seen. These thin spindly fibres show that without the addition of phosphoglycerol, the pili cannot clump together.

This is important medically as Type IV pili bundle formation and N. meningitidis aggregation for infection are linked. Interestingly it was not the aggregation that was affected by removing the phosphoglyerol but the ability of individual bacteria to leave the aggregate to infect other parts of the body. In wild-type bacteria, the pptB gene is strongly activated only after several rounds of division within the aggregate, so it looks like the addition of phosphoglycerol acts as a switch, communicating to the bacteria that enough of them have aggregated and it is now time to leave. If the pptB is activated due to large numbers of bacteria it could act as a communication of the population density - signalling to the individual bacteria that the current location is far too crowded, and it has better chances of survival if it leaves.

Chamot-Rooke J, Mikaty G, Malosse C, Soyer M, Dumont A, Gault J, Imhaus AF, Martin P, Trellet M, Clary G, Chafey P, Camoin L, Nilges M, Nassif X, & Duménil G (2011). Posttranslational modification of pili upon cell contact triggers N. meningitidis dissemination. Science (New York, N.Y.), 331 (6018), 778-82 PMID: 21311024
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