Bacteria of the phylum Planctomycetes have been postulated to be the ‘missing link’ between prokaryotes and eukaryotes. Although phylogenetically the Planctomycetes were grouped into Gram-negative bacteria, it has been reported that they have no outer membrane. Here we present 1D-gel-LC/MS/MS based proteomics data of Planctopirus limnophila membraneswhich in combination with super resolution light microscopy, cryo electron tomography and bioinformatics suggest an altered Gram-negative cell plan for Planctopirus limnophila.