PVC bacteria: variation of, but not exception to, the Gram-negative cell plan

• Planctomycetes–Verrucomicrobia–Chlamydiae (PVC) bacteria are derived from a Gram-negative (G–) ancestor.
• The PVC cell plan is derived from a G– cell plan.
• All membranes in PVC members are equivalents of membranes in G– bacteria.
• There are no exceptions to the bacterial cell-plan definition.

Planctomycetes–Verrucomicrobia–Chlamydiae (PVC) bacteria have features that differentiate them from classical Gram-negative (G–) bacteria. One such feature is their complex endomembrane system. Based on the difference of membrane organization and compartment identity, PVC bacteria were proposed to form an exception to the bacterial G– cell plan. Here I argue that all PVC membranes are derived from G– membranes, and that their organization and the compartments they form are similar to those of G– bacteria. I suggest that PVC membrane organization should be evaluated within a G– framework and as a variation of it.