The bacteria-RBC suspensions were gently resuspended with an addi

The bacteria-RBC suspensions were gently resuspended with an additional 100 μL of PBS and then the plates were centrifuged. The supernatants were transferred to new plates, on which optical density was measured at 492 nm. In a previous study, we have confirmed that the hemolytic activity induced by the adenylate cyclase toxin can be excluded from this measurement system (6). Statistical analyses were performed using

Student’s t-test, P < 0.05 INK 128 chemical structure being considered statistically significant. When B. bronchiseptica is grown on SS liquid medium, type III secreted proteins are detected in the bacterial culture supernatants (6, 16). The SS liquid medium used contained casamino acids as the amino acid source. In a previous study, we empirically found that maximal production of type III secreted proteins can be detected by a certain grade of casamino acids suitable for DT production (data not shown). Although various grades of casamino acids are commercially available, because production of DT in Corynebacterium diphtheriae is induced by iron starvation, the DT grade is processed to have a low iron concentration BTK inhibitor (24). Therefore, we postulated that iron starvation would affect production of type III secreted proteins in B. bronchiseptica. To test

this, B. bronchiseptica was grown in parallel in iron-replete and iron-depleted SS media and the secreted proteins prepared from the bacterial culture supernatants subjected to SDS-PAGE and then stained with CBB (Fig. 1a). Under iron-depleted conditions, the band intensities of the type III secreted proteins (BteA, BopB, BopN, BopD, and Bsp22) increased dramatically compared to those of the same proteins under iron-replete conditions. Conversely, the band intensities of type III secreted proteins were decreased by addition of 36 μM FeSO4 to the iron-depleted SS media (Fig. 1b). In contrast, type III secreted proteins remained unaffected by the addition of other divalent cations such as Mn2+ or Ni2+ (Fig. 1b). Collectively, these results suggest that iron starvation enhances secretion of type III secreted proteins in B. bronchiseptica. In Bordetella, BvgAS regulates

many virulence factor genes, including T3SS genes, and is repressed by an excess amount of MgSO4 (∼ 40 mM) in the culture media. As shown in Fig. 1c, the increase in secretion Etoposide of type III secreted proteins under iron-depleted conditions is completely repressed by addition of 40 mM MgSO4 to the culture media. These results suggest that the iron-responsive expression of type III secreted proteins is under the control of the BvgAS regulatory system. To analyze whether iron starvation also affects expression of other BvgAS-regulated genes, bacteria were grown in parallel in iron-replete and iron-depleted SS media, and protein samples prepared from the whole cell and culture supernatants. Production of FhaB, CyaA, Prn, and DNT was then detected by immunoblot analysis (Fig. 2).

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