The three functions associated with essential pathways are indicated by color: pale blue, cell envelope; gray, energy production; light green, processing of genetic information. Numbers are SSA#; red number, essential gene; black number, nonessential gene; solid arrow, an enzymatic reaction; dashed arrow, multistep pathway; blue dashed arrow, products involved in cell wall and membrane formation; block arrow, product from one pathway serving as input to another pathway; oval with bold arrow, transporter; slash, separating paralogs. Ado, adenosine; Cyd, cytidine; DAG, 1,2-diacylglycerol; DHAP, dihydroxyacetone phosphate; DHF, dihydrofolate; L-G3P, sn-glycerol 3-phosphate; Guo, guanosine; LPA, lysophosphatidic acid; LTA, lipoteichoic acid; PA, phosphatidic acid; PGP, phosphatidylglycerophosphate; PPP, pentose phosphate pathway; TCS, two-component system; THF, tetrahydrofolate; Urd, uridine. In nucleotide biosynthesis, symbols are used to represent essential genes that participate in multistep reactions: SSA_1865 (green circle), SSA_0848 (yellow oval), SSA_2263, SSA_0771 (orange circles) and SSA_0768 and SSA_0770 (brown oval). Essential genes associated with ribosome and aminoacyl-tRNA biosynthesis are not indicated here, nor are SSA_0575, SSA_0800 and SSA_1903, which could not be categorized into these pathways.