FIGURE 4: D-Serine reduces nuclear foci observed in HeLa cells. HeLa cells were infected for 4 h with E. coli Nissle 1917 or DH10B hosting BAC-pks (MOI = 400). Infections were performed with and without the addition of 1 mM D-Serine to the growth media. At 8 h post infection, cells were washed, fixed, and stained with anti-γ-H2AX antibody. (A) Cells were examined by confocal microscopy for DNA in cyan and phosphorylated histone H2AX protein in magenta. Images of uninfected, and pks⁺ infected cells are shown, scale bar = 50 μm. (B) Intracellular levels of phosphorylated histone H2AX were measured by flow cytometry 8 h after infection. Dot plots reveal the percentage of viable cells fluorescing in the γ-H2AX channel, 100k events were analysed for each sample.