Mapping of the P. gingivalis essential genes. In blue in the outermost ring are shown the putative P. gingivalis essential genes identified by transposon mutagenesis of strain ATCC 33277. Blue arrows depict the orientation of the essential genes. Genetic loci for positive strand (outer set of arrows) are shown in the outermost circle and genetic loci for the negative strand are shown in the innermost ring. In red tick marks are coding sequences for P. gingivalis strain W83, in green are coding sequences for strain W50 and in blue are coding sequences for strain TDC60. Shaded black area represents GC-content for given regions. CGViewer (http://stothard.afns.ualberta.ca/cgview_server/) was utilized to visualize the entire circular genome of P. gingivalis strain ATCC 33277 with the putative essential genes labeled . NCBI FASTA files of P. gingivalis strains W83, W50 and TDC60 were used for BLAST matching to the ATCC 33277 base genome.