Many of the same genes or classes of genes which were ranked highly by MHS are also identified by GCS. RNA polymerase RpoB/C, topoisomerase, gyrase, and several tRNA synthetases all rank highly by both methods. However, several interesting

genes not identified by MHS are placed at the top of the GCS ranking. For example, pyruvate phosphate dikinase, PPDK, has previously been identified by pathway analysis as a potential drug target [39]. By MHS, PPDK was ranked at position 309; GCS ranking placed it at position 3. Table 4 Top 20 wBm genes ranked by GCS. Annotations taken from the Refseq release of the wBm proteome. Rank GCS GI Annotation 1 101 58584652 2-oxoglutarate dehydrogenase complex, E1 component 2 101 58584298 Topoisomerase IA: TopA 3 101 58584469 Pyruvate phosphate dikinase 4 101 58584904 DNA-directed RNA polymerase: RpoB/RpoC 5 101 58584952 Ribonucleotide-diphosphate EPZ 6438 reductase alpha subunit 6 101 58584808 ATP-dependent Lon protease 7 101 58584662 DNA gyrase subunit A 8 101 58584705 Succinate dehydrogenase 9 101 58584602 Translation elongation factor, GT-Pase: FusA 10 101 58584729 Threonyl-tRNA synthetase 11 101 58584633 NADH dehydrogenase gamma sub-unit 12 101 58584752 Molecular chaperone: DnaK 13 101 58584862

Leucyl-tRNA synthetase 14 101 58584524 Translocase 15 100.994 58585021 DNA gyrase, topoisomerase II, B sub-unit: GyrB 16 100.989 58584924 GTP-binding protein: LepA 17 100.987 58584410 ATP-dependent Zn protease: HflB 18 100.986 58584731 NADH:ubiquinone oxidoreductase, NADH-binding, chain GSK2879552 supplier F 19 100.974 58584620 Isoleucyl-tRNA synthetase Phospholipase D1 20 100.974 58584756 DNA polymerase III alpha subunit Plotting MHS versus GCS demonstrates the

identification of complementary sets of essential genes The two methods of essential gene prediction used in this study identified complementary partially overlapping sets of wBm genes. Identification of a gene by both methods bolsters confidence in a prediction of essentiality. Genes uniquely identified by an individual method may represent, for MHS, genes essential to Combretastatin A4 nmr general bacterial processes; and for GCS, genes specifically important to the Rickettsiales order. To assess the distribution of essentiality prediction by both methods, the MHS and GCS for each wBm gene was graphed as a scatter plot (Figure 5). Lines indicating the empirically determined thresholds for the prediction of essentiality by each method produce four quadrants showing the classes of predicted essential genes. The upper-right quadrant contains 245 genes predicted essential by both methods. The upper-left quadrant contains 299 genes which are not similar to essential genes in more distantly related bacteria, but are still highly conserved across Rickettsiales. These genes represent a promising class of drug targets which are likely to be more specific to wBm.