Fig. 6: S. pneumoniae strains can evolve different mechanisms to overcome the essentiality of formate tetrahydrofolate reductase (SP_1229).
From: A bacterial pan-genome makes gene essentiality strain-dependent and evolvable
a, Role of the product of the strain-dependent essential gene SP_1229 in the one-carbon pool by folate pathway and suppressor mutations in PG16 bypassing SP_1229 essentiality (boxes with white background). Dashed arrows indicate multiple metabolic reactions (not-shown) that connect the depicted pathways. Two of these mutations, present in two independent backgrounds, create premature stop codons in SP_0918 (Q136*) and SP_1378 (Q319*), which connect to the one-carbon pool by folate pathway through the S-adenosyl-methionine cycle. SP_0918, when deleted in strain D39, diminishes the production of spermidine72, while SP_1378 codes for an S-adenosyl-l-methionine (SAM)-dependent RNA-methyltransferase. Three additional PG16-SP_1229 knockouts contain suppressor mutations in genes involved in guanosine ribonucleotide metabolism and (p)ppGpp biosynthesis (SP_0012-T104A and SP_1645-S310F, SP_1645-A378T and SP_1738-Y35C, respectively). b, Growth of WT strains PG04, TIGR4 and PG16, and their SP_1229 knockouts in rich medium in the presence/absence of the tetrahydrofolate (THF) synthesis inhibitory drug SXT. SP_1229 is non-essential in PG04 and TIGR4, and essential in PG16. Data are from n = 3 biologically independent samples per condition, independent repetition of each experiment (3) showed similar results. Error bars represent s.d. c, Identification of genetic interactions through Tn-seq using libraries constructed in two backgrounds where SP_1229 is non-essential (PG04 and TIGR4) and two knockouts derived from PG16 with different suppressor mutations (SP_0918 Q136* and SP_1378 Q319*).
