Today, several hundred complete genomic sequences of Escherichia and Shigella species are available. The genome sequence of the type strain of E. coli has been added to this collection not before 2014.[43] Comparison of these sequences shows a remarkable amount of diversity; only about 20% of each genome represents sequences present in every one of the isolates, while around 80% of each genome can vary among isolates.[30] Each individual genome contains between 4,000 and 5,500 genes, but the total number of different genes among all of the sequenced E. coli strains (the pangenome) exceeds 16,000. This very large variety of component genes has been interpreted to mean that two-thirds of the E. coli pangenome originated in other species and arrived through the process of horizontal gene transfer.[51] - en.wikipedia.org