Researchers analysed metagenomic data from 1,618 patients with inflammatory bowel disease (IBD) and 791 healthy individuals as controls and identified invertible DNA orientations in Bacteroidales genomes. Of those 311 invertible regions, 147 were markedly different in terms of orientation in patients with IBD.

The inverted regions included, among others, the anti-inflammatory PSA promoter of Bacteroides fragilis, which induces regulatory T (Treg) cells in the colonic lamina propria of mice. In healthy individuals, the PSA promoter is in its ‘on’ orientation, whereas in patients with IBD, it is in its ‘off’ (inverted) orientation.