I do love Staph aureus, despite the heartache of studying it for my PhD, I still can't help but be fascinated by it. From the creative ways that it ducks under the immune system, to the fact we were studying small RNA gene regulation in Staph before it was cool, Staph aureus is great.
However, during my undergraduate, I was captivated by cyanobacteria and was fortunate enough to do a project on their gliding motility. The blue-green cultures always looked so impressive in their rows on the incubator shelves. They were huge and you could see a lot of structures under the microscope and you can even see some of the Oscillatoria cells with the naked eye.
This isn't enough to make cyanobacteria my favourite microbes, but the ability to photosynthesise gets them closer. I've always been fascinated by the elegance of photosynthesis from when I was in school and the fact that these microbes can carry out this string of complex reactions to make sugar from light makes them pretty special.
However, the real reason that cyanobacteria are my favourite is because not only do they photosynthesise, but many of them also fix nitrogen. I mean, talk about the complete package. Many cyanobacteria have differentiated cells called heterocysts which are specifically for fixing nitrogen. By compartmentalising photosynthesis and nitrogen fixation, cyanobacteria can carry out two complex biochemical pathways that would otherwise be difficult to carry out in the same organism.