May 10, 2016 at 04:34PM

Yesterday I Learned: 1) Bacillus subtilis (a commonly-used lab bacteria) has an interesting stress response. When B. subtilis (or "B. sub", as it's affectionately called in the lab) is stressed, it can respond in two different ways. B. sub can sporulate, meaning it encysts itself in some sort of hard, dehydration-proof case and goes into stasis, like a tardigrade. B. sub spores can last out whatever harsh conditions triggered the stress, only popping open when conditions are good again (apparently sporulated B. sub commonly survive being cooked in bread, and can cause the bread to go "ropy" (don't worry, though, B. sub is harmless unless you're severely immunocompromised)). Sometimes, though, a stressed B. sub can instead enter a state called "competency". A "competent" bacteria is one that is totally, utterly desperate for a solution to its problems, and tries to fix them by ingesting any nearby DNA in the hopes that some of it will contain a useful fix. Remarkably, there's enough DNA floating around, of enough variety, that this strategy is actually worth pursuing some of the time, and when it works, it means the bacteria can keep on growing -- much better than going dormant for years and hoping to land in a good spot to grow. It's still riskier than sporulation, though, and most of the time a competent bacteria is just going to die. The correct strategy for B. sub appears to be for most bacteria in a population to sporulate while a few enter competency and hope to get lucky. Yesterday I learned that B. sub has a more interesting competency pattern than I thought. It turns out that when B. sub becomes competent, it is virtually always a temporary state -- after a few hours, it swings back into sporulation and goes dormant. The genetic regulatory network that controls this behavior can be boiled down to a relatively simple model. There's a competency-triggering gene which, when high, triggers competency, and when low, allows sporulation (if other triggers are present to enter competency). The control gene activates the expression of two transcription factors that feed back to control its own expression -- a fast-acting activator and a slow-acting repressor. Normally, the competency gene is held at very low levels, where it fluctuates a lot. Occasionally, stochastically, it will happen to get produced enough to turn on its activator, which starts a feedback loop that kicks production WAY up and sending the cell into competency. Eventually, though, the slow-acting repressor kicks in and turns down expression of the competency-control gene. The cell goes back out of competency, and it can sporulate. The end behavior of this whole system is that B. sub can, if stressed, probabilistically and temporarily enter competency for a while before reliably coming back to sporulation, which is thought to be the (more or less) optimal strategy for survival under stress. 2) Matplotlib (python's most popular plotting module) has a pretty rich palette of built-in colors. There's a table of available colors in this stack overflow answer: http://ift.tt/21TVYIi 3) ...more than I think I wanted to know about printing labels....