J Bacteriol Virol.  2016 Sep;46(3):128-134. 10.4167/jbv.2016.46.3.128.

Transcriptional Analysis of the iagB within Salmonella Pathogenicity Island 1 (SPI1)

• Lim S
• Choi J
• Kim D
• Seo HS

• KMID: 2353847
• DOI: http://doi.org/10.4167/jbv.2016.46.3.128

Abstract

HilA is a central regulator of Salmonella pathogenicity island 1 (SPI1), which is necessary for host invasion by Salmonella and induction of gastroenteritis. The iagB lies downstream of hilA and is thought to be co-transcribed with hilA, but iagB expression has not yet been analyzed directly. In this study, iagB expression in various mutant strains was measured to determine whether the expression pattern was similar to that of hilA. A β-galactosidase assay revealed that iagB expression was greater under shaking than standing culture condition. iagB expression was decreased in relA/spoT and ihfB mutants but not in luxS mutant, in line with previous reports on hilA expression. The hilA and iagB mRNA levels decreased by approximately 2-fold in arcA mutant grown aerobically and increased by approximately 10-fold in fnr mutant grown anaerobically. Although the fold changes in hilA and iagB mRNA level differed in hfq mutant strain, the patterns of time- and Hfq-dependent regulation were similar for both genes. Thus, iagB and hilA exhibited similar expression patterns in various mutational backgrounds and under different growth condition.

Keyword

Salmonella Typhimurium; Salmonella pathogenicity island 1 (SPI1); HilA; IagB

MeSH Terms

Gastroenteritis
Genomic Islands*
RNA, Messenger
Salmonella typhimurium
Salmonella*
Virulence*
RNA, Messenger

Figure

• 

  Figure 1. Transcriptional analysis of iagB under different growth conditions. The S. Typhimurium strain harboring a chromosomal iagB:: lacZY fusion was grown in LB medium under shaking (●) or standing conditions (○). The expression level was determined by measuring the β-galactosidase activity (Miller units) at the indicated times. Data are presented as the mean ± standard error of three independent experiments performed in duplicate.

• 

  Figure 2. Transcriptional analysis of iagB in different mutant strains. The β-galactosidase activities (Miller units) of chromosomal iagB::lacZY were measured in ΔluxS (A), ΔppGpp (ΔrelA/ΔspoT)(B), and Δ ihfB (C) strains at 4 h p.i. (early stationary phase) and 12 h p.i. (late stationary phase) under shaking and standing culture conditions, respectively. Data are presented as the mean ± standard error of three independent experiments performed in duplicate.

• 

  Figure 3. Transcriptional analysis of hilA and iagB in arcA and fnr mutants. The mRNA levels of hilA and iagB were determined by qRT-PCR. Total RNA was isolated from strains grown for 4 h under shaking and standing culture conditions. The values for the relative expression were determined by defining the mRNA levels from the wild-type strain as 1. The expression levels of the target genes were normalized to 16S rRNA gene. Data are presented as the mean ± standard error of three independent experiments performed in duplicate.

• 

  Figure 4. Transcriptional analysis of hilA and iagB in hfq mutants. The mRNA levels of hilA and iagB were determined by qRT-PCR. Total RNA was isolated from strains grown for 4 h and 12 h under shaking culture conditions. The values for the relative expression were determined by defining the mRNA levels from the wild-type strain as 1. The expression levels of the target genes were normalized to 16S rRNA gene. Data are presented as the mean ± standard error of three independent experiments performed in duplicate.

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