The only living thing smaller than Mycoplasma pneumoniae is a virus, and we could debate whether viruses are alive.
That is to say, Mycoplasma pneumoniae is tiny. Wee. Itsy. Bitsy. If you think this period (.) is small, well, it's like a football stadium for Mycoplasma pneumoniae.
It has one of the smallest known genomes, with 816 kilobase pairs, nearly three thousand times smaller than the genome of maize, enough info to make only a few hundred proteins. Not enough genes for much of a life of its own, which is why it has a parasitical eye on you and me.
Three papers in the 27 November issue of Science provide and exhaustive analysis of Mycoplasma pneumoniae, including its proteins and metabolism. Here's Nicholas Wade of the New York Times:
The bacterium is a collection of some 200 specialized protein machines. The machines are composed of individual proteins, which recognize each other and assemble into complexes. Some of the machines make copies of the genes embodied in the DNA of the bacterium's genome. Others, called ribosomes, synthesize proteins according to the genetic instructions they receive. Another class, called chaperones, make sure the new proteins fold up correctly. Then there are processing machines in which each component carries out one step of a multistage chemical process.And here is an eye-popping schematic from Science of Mycoplasma pneumoniae's metabolism. Click to enlarge, and again if you wish.
The story I want to tell is this: All of this fabulous machinery is humming away in a living organism so small that a thousand could line up on this period. Even the simplest bacterium is wonderfully complex. And, perhaps equally amazing, is that researchers are able to analyze in such exquisite detail what is happening on so small a scale. It's like figuring out the blueprint of a modern petrochemical plant that has been reduced to a size that would let a million petrochemical plants fit on the head of a pin.