I have read quite some articles but I can't figure out the main reason for gc content deviation in prokaryotes. In eukaryotes I can understand it, because the genome isn't composed at random, like TATA boxes and CpG island, because they are important for functioning in the production of proteins.
However in prokaryotes there is such a variety, GC% is ranging from 20% up to 70%. Most of the time it depends on the environment, high temperature needs a stable genome (= high gc content).
I also read the answer to this question How does GC-content evolve? however it's still not clear to me. I hope someone can explain the deviation a little bit more.
Prokaryotes have an AT drift, but what mechanism causes some of these bacteria to higher their GC% instead of lowering it.