Figure 6: Salmonella infection arrests host cells in the G2/M phase of the cell cycle.

(a) Percentage of HeLa cells infected with Salmonella (MOI 25), (b) GFP expression determined using qRT–PCR and (c) CFU quantification upon treatment with DMSO (control) or RO-3306 (9 μM), an inhibitor of CDK1. Samples were collected at 14 h.p.i. (d) Percentage of HeLa cells in the different stages of the cell cycle upon Salmonella infection (MOI 50) at the indicated times post infection. Analysis is shown for fraction of cells with internalized Salmonella (Salmonella+) and the bystander fraction (Salmonella−). Cell cycle stage distribution was determined using FACS, following propidium iodide staining. Representative cell cycle profiles for 8, 12 and 20 h.p.i. are shown. Population of cells in G2 is significantly increased in Salmonella+ compared with Salmonella− fractions, from 12 h.p.i. onwards (P<0.05, two-tailed Student’s t-test). (e) Percentage of HeLa cells in the different stages of the cell cycle, and (f) representative cell cycle profiles, upon infection with wild-type (MOI 100) and different mutant Salmonella strains (MOI 250). Analysis is shown for fraction of cells with internalized Salmonella. Bystander population from the cells treated with wild-type Salmonella (Salmonella−) is shown for comparison. Population of cells in G2 for the Salmonella+ fraction is significantly decreased in ΔSPI-2 and ΔSpvB, compared with WT (P<0.05, two-tailed Student’s t-test). Data are shown as mean±s.e.m. 2N and 4N in d,e indicate cells having diploid or tretraploid DNA content, respectively. *P<0.05, **P<0.01, ***P<0.001, two-tailed Student’s t-test; n≥3.