Abstract
BackgroundSpiC encoded within Salmonella pathogenicity island 2 on the Salmonella enterica serovar Typhimurium chromosome is required for survival within macrophages and systemic infection in mice. Additionally, SpiC contributes to Salmonella-induced activation of the signal transduction pathways in macrophages by affecting the expression of FliC, a component of flagella filaments. Here, we show the contribution of SpiC in flagellum synthesis.ResultsQuantitative RT-PCR shows that the expression levels of the class 3 fliD and motA genes that encode for the flagella cap and motor torque proteins, respectively, were lower for a spiC mutant strain than for the wild-type Salmonella. Further, this mutant had lower expression levels of the class 2 genes including the fliA gene encoding the flagellar-specific alternative sigma factor. We also found differences in flagella assembly between the wild-type strain and the spiC mutant. Many flagella filaments were observed on the bacterial surface of the wild-type strain, whereas the spiC mutant had only few flagella. The absence of spiC led to reduced expression of the FlhD protein, which functions as the master regulator in flagella gene expression, although no significant difference at the transcription level of the flhDC operon was observed between the wild-type strain and the spiC mutant.ConclusionThe data show that SpiC is involved in flagella assembly by affecting the post-transcription expression of flhDC.
Highlights
SpiC encoded within Salmonella pathogenicity island 2 on the Salmonella enterica serovar Typhimurium chromosome is required for survival within macrophages and systemic infection in mice
The data show that SpiC is involved in flagella assembly by affecting the posttranscription expression of flhDC
Several investigators report that SpiC is required for the translocation of SPI-2 effector proteins into the target cells by interacting with SsaM, a SPI-2 encoded protein [10,11,12]. In addition to these reports, we have shown that SpiC contributes to Salmonella-induced activation of the signal transduction pathways in macrophages, leading to the production of mediators such as interleukin-10, prostaglandin E2, and the expression of the suppressor in cytokine signaling 3 (SOCS-3) that are thought to have important roles in Salmonella virulence [13,14,15]
Summary
Quantitative RT-PCR shows that the expression levels of the class 3 fliD and motA genes that encode for the flagella cap and motor torque proteins, respectively, were lower for a spiC mutant strain than for the wild-type Salmonella. This mutant had lower expression levels of the class 2 genes including the fliA gene encoding the flagellar-specific alternative sigma factor. The absence of spiC led to reduced expression of the FlhD protein, which functions as the master regulator in flagella gene expression, no significant difference at the transcription level of the flhDC operon was observed between the wild-type strain and the spiC mutant
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