Worms and bugs in the mountains

Reposted from the UCVM helminthology blog: The Banff Conference on Infectious Diseases (BCID) ran this year from Wed-Sun over the first week of June. It has always been organized jointly between the Universities of Calgary and Alberta, and as usual they brought in many top researchers from around the world. I have attended twice in the past, back when I was working in microbiology and infectious diseases, but this time our lab went to represent parasites. This is actually something that I felt was somewhat missing from my previous degree; in classes or seminars or conferences we heard about bacteria, viruses, prions, and malaria, but almost never about parasitic worms. So my supervisor, James Wasmuth, gave a talk on Trichinella spiralis, and I presented a poster about our work on worms. There were a lot of very interesting talks at the conference. One that stuck in my mind is from a group looking to quantify the response of a single bacterial cell under different conditions. Their rather interesting approach was to use nanotechnology to create bacterial traps. They manufactured a chip with a few dozen very small structures on it, where each was in the shape of a “C” that was just large enough to accommodate a single bacteria inside. When the slide was exposed to heat, the material would swell shut, effectively trapping that bacterium in a set location. You could then expose the cells to any treatment you like, measure a response, and repeat; each measurement would be on the exact same cell so you wouldn’t have to measure only population level data. Another talk that I found very interesting had to do with horizontal gene transfer in bacteria. It is a well known and studied phenomenon, that many bacterial species are able to uptake DNA from their environment, and that many of them integrate it into their own genomes. It is a common mechanism of spreading useful genes (often virulence factors) even between divergent species. But when you think about it, taking up a whole operon from a different bacteria carries with it quite a bit of risk. A bacteria doesn’t want something that is constantly draining resources for no benefit, or worse, some product that would interfere with the standard cellular processes. And for many complex features, such as a type-6 secretion system or a toxin/anti-toxin pair, all of the parts would have to begin working at the same time in order to be at all useful or safe. It is extremely likely that any foreign DNA would have to undergo many specific mutational changes in order to begin to function properly within the cell, which is extremely unlikely to occur in a short time period. All of these traits would be strong selective pressures to kick out foreign DNA, but on the other hand the rapid spread of new genetic material can provide a very beneficial evolutionary response to changing environments. It turns out that Salmonella uses the histone-like nucleoid structuring (H-NS) system to have their cake and eat it too. The genomes of different species of bacteria often have very different G-C content (can range from 25%-75%); Salmonella has a relatively high level. This means that any foreign DNA it takes up will likely be comparatively A-T rich. The H-NS system exploits this fact, and is able to bind to A-T rich regions of the genome regardless of the specific sequences. These proteins effectively supercoil the genome at these regions, preventing transcription at very low cost to the cell. Salmonella is therefore able to maintain a diverse reservoir of genes that are not actually active, but can collect mutations over time and quickly be turned on when the appropriate infrastructure comes into being. Systems like these have been found in several other bacterial species, and may help to explain how multi-part complex traits sometimes seem to suddenly spring into existence. So quite an interesting conference, and a good opportunity for me to see new research that is not directly related to what I do. Hopefully some people found our work as interesting as I found theirs.


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