A) Percentage of essential protein-coding genes; B) Correlation between essential gene set size and genome size. Abbreviations: abayl-min (Acinetobacter baylyi ADP1, minimal medium); bfrag (Bacteroides fragilis 638R); bpseu (Burkholderia pseudomallei K96243); bsubt (Bacillus subtilis 168); bthai (Burkholderia thailandensis E264); ccres (Caulobacter crescentus NA1000); ecoli (Escherichia coli K-12); ftula (Francisella tularensis novicida U112); mgeni (Mycoplasma genitalium G37); mmari (Methanococcus maripaludis S2, rich medium); mmarimin (Methanococcus maripaludis S2, minimal medium); mpulm (Mycoplasma pulmonis CT); mtube-min (Mycobacterium tuberculosis H37Rv, minimal medium); pging (Porphyromonas gingivalis ATCC 33277); sente-SL1344 (Salmonella enterica typhimurium SL1344); sente-Ty2 (Salmonella enterica typhi Ty2); ssang (Streptococcus sanguinis SK36, minimal medium).