So, I'm writing my introductory microbiology exam, looking for an interesting organism to make the focus of the exam. I can't divulge what organism I chose, in the 1/10,000,000,000 chance that one of my students is reading this, but I can say what I didn't choose: an Archaeal cell called the "ANME organism." This is a critter that makes a living by oxidizing methane under anaerobic conditions, usually in ocean sediments. It's ecologically significant, turning over petagrams of methane every year, and metabolically cool, since no-one really understands how it makes any energy at all. The reactions it uses shouldn't be enough to allow it to live, just like you couldn't live on a diet of one sugar cube per day. But, live it does, just very slowly.
I worked with Escherichia coli, the "standard" laboratory organism. Give it good food, and a single E. coli cell becomes two cells in about 20 minutes. If you had an E. coli cell that was asleep, and tried to get it to start growing, the time before it started metabolizing--its lag time--would be about ten to fifteen minutes. I did some experiments where I gave it really bad food, and it took about two hours to double, and had a lag time of half an hour--and I hated those experiments, because they took an entire 24-hour day to do.
But, it could be worse. I could study the ANME organism--or try to. The estimated doubling time for ANME is seven months, and while nobody has done the experiment, the calculated lag time is sixty years! The work I did for my PhD, if done in ANME instead of E. coli, would take the better part of millennium.
I should tell my PhD advisor. He wanted me to graduate sooner.