That’s a great question. For a long time, the general rule of thumb was that only eukaryotes had histone proteins. There were a small number of archaea and bacteria with some “histone-like proteins” that were only somewhat similar. But recently, more evidence for histones in prokaryotes has been coming out, like this paper published about 9 months after I posted this video: academic.oup.com/bioinformatics/article/35/14/2349/5232221
