B, Cartoon schematic of the two possible translocon outcomes for binding of ColE9 W39A to BtuB and their implications on vitamin B12 import in E. coli 113/3. The W39A mutation within the TBE of ColE9 (orange) impairs TolB (blue) binding thereby uncoupling the OM components of the translocon from the energized TolQ-TolR-TolA complex in the inner membrane. If threading of the ColE9 IUTD through OmpF (green) has no impact on ColE9 binding to BtuB (grey) then vitamin B12 (red) cannot enter cells to support growth. In contrast, if OmpF threading disengages ColE9 from BtuB then vitamin B12 can enter cells to support growth. 