Complex phase variation in EPEC. (A) Two overlapping 'funnel' formations indicate a complex structure of PV. A large inversion (around 2,200 bp) and a smaller inversion (around 1,800 bp) coincide within the same module. (B) Sequence analysis revealed three homologous inverted repeats in the locus (green arrows), which allow for the two inversions. Further analysis indicated four possible variants. Each variant can mutate into two of the other variants by any of the two inversions. (C) While the large inversion retains stable proportions in all clones, the small inversion is unstable and displays great variance between samples. Error bars represent standard deviation between five independently sequenced and analyzed single colonies.