You gain more and more copies of genes which help you convert the chemical soup you are floating in into energy - and copies of yourself! This means you get bigger and bigger.

Your multiple plasmids carry all the genes you need to express the proteins for several different chemical pathways. This is great, because no matter what chemicals you find yourself floating in, you can use it to reproduce.

However, it is actually becoming a bit of a problem, as groups of genes which work well together are getting longer and longer as well as more numerous. They are getting in each other’s way! You need some way to pack them in better, so that only the currently useful ones are exposed.

Genes are often thousands of times longer than they are wide, resembling massive threads, and one well known way to tidy away threads is to wind them on a spool. There are several different chemicals which can act as a spool, but two in particular stand out with the lower cost for a given functionality.

One costs more, but allows more efficient packing, and is called histone. The other is known as HU.