FIG 1.

Endogenous spermidine biosynthesis is involved in the E. coli colibactin-associated megalocytosis phenotype. (A) Presentation of the polyamine biosynthetic pathways (34). DH10B pks⁺ mutants with mutations of genes speB, speC, speE, and speG were tested for the megalocytosis phenotype in infected HeLa cells, as previously described (1). The phenotypes of HeLa cells resulting from infection with the different mutants are shown. (B and C) Cytotoxic effects of colibactin produced by E. coli strains DH10B pks⁺, M1/5, and SP15 and their derivatives were determined by quantification of megalocytosis. At the end of HeLa cell infection, the methylene blue protein staining was quantified by measurement of absorbance at the optical density at 660 nm. The multiplicity of infection (MOI) was 200. Data were pooled from three independent experiments. ***, P < 0.001, and **, P < 0.01, by 1-way analysis of variance (ANOVA). All bar graphs show mean values ± standard errors of the mean (SEM). NS, not significant.