October 28, 2016 at 11:13PM

Today I Learned: 1) The E. coli genome apparently forms a solenoid-like helix with a turn size of about 100,000 bp. This means that stuff like sigma factors that recruit other enzymes to specific locations in the genome can also affect locations that appear to be very far away, but are physically close to each other in the cell. Note that the diameter of this solenoid is significantly bigger than the diameter of an E. coli. I believe this works out because there is also higher-order coiling of the genome. Also note that this is old news to scientists who study Eukaryotes. I just didn't know that it also happened reliably and repeatably in bacteria, or that the bacterial genome formed such a huge loop. 2) The single most important chemical in modern dry-cleaning is perchloroethylene (or PERC). It's incredibly cheap, incredibly good at removing stains, and somewhere between midly and very toxic (and probably a carcinogen). It's nasty stuff to work with, but it's very difficult for dry-cleaners to get away from. France recently put a ban on PERC, set to go into effect in 2022. The iGEM team of Paris-Bettencourt decided to interview every dry-cleaner in Paris, in person, to determine what effect the ban has had so far and what dry cleaners are looking to replace it with. It turns out that a) a lot of dry cleaners are still using PERC, b) a lot of dry cleaners have moved away from PERC, c) by region, PERC use is negatively correlated with immigrant populations, d) a nontrivial number of dry cleaners report feeling sick around PERC, and e) a lot of dry cleaners don't really know how they can survive without PERC -- it's just too damned economical. 3) Bacteriosins are a class of toxic protein secreted by bacteria to kill or inhibit closely-related species. They are much more effective than standard lab antibiotics, and after fifty years of use in the food industry, we still don't see resistance to them in any meaningful amounts. Unfortunately, they're also quite narrow-spectrum, and they aren't particularly useful medicinally in part because they break down very quickly in the stomach.