Fig. 6: Host-derived nitrite represses T3SS1 gene expression during infection.

a Nitrite concentration measured in the culture medium of Caco-2 cells infected with the indicated strains in the presence or absence of aminoguanidine (AG). All error bars represent mean ± standard deviation (n = 3 biologically independent experiments). b Nitrate concentration measured in the culture medium of Caco-2 cells infected with the indicated strains in the presence or absence of AG. All error bars represent mean ± standard deviation (n = 3 biologically independent experiments). c–f Quantitative RT-PCR analysis of T3SS1 gene expression in V. parahaemolyticus during infection. Caco-2 cells were infected with WT (WT + Caco-2), ΔvbrK (ΔvbrK + Caco-2) or ∆vpa1199-1201 (∆vpa1199-1201 + Caco-2) and RNA was collected from the infected samples for qRT-PCR analysis of exsC (c), vopD1 (d), vp1668 (e) and vp1662 (f). Transcripts of these genes in WT and ΔvbrK in the LB medium were also included as controls. Bars indicate average fold changes relative to WT under LB growth condition without AG. All error bars represent mean ± standard deviation (n = 3 biologically independent experiments). (a-f) Statistical significance was calculated using two-tailed multiple t test with Bonferroni correction. Asterisks indicate P values *P < 0.05, **P < 0.005, and ***P < 0.0005 (exact P value for each comparison was shown in the figures).