Abstract
BackgroundAvian pathogenic E. coli (APEC) are associated with extraintestinal diseases in poultry. The pstSCAB-phoU operon belongs to the Pho regulon and encodes the phosphate specific transport (Pst) system. A functional Pst system is required for full virulence in APEC and other bacteria and contributes to resistance of APEC to serum, to cationic antimicrobial peptides and acid shock. The global mechanisms contributing to the attenuation and decreased resistance of the APEC pst mutant to environmental stresses have not been investigated at the transcriptional level. To determine the global effect of a pst mutation on gene expression, we compared the transcriptomes of APEC strain χ7122 and its isogenic pst mutant (K3) grown in phosphate-rich medium.ResultsOverall, 470 genes were differentially expressed by at least 1.5-fold. Interestingly, the pst mutant not only induced systems involved in phosphate acquisition and metabolism, despite phosphate availability, but also modulated stress response mechanisms. Indeed, transcriptional changes in genes associated with the general stress responses, including the oxidative stress response were among the major differences observed. Accordingly, the K3 strain was less resistant to reactive oxygen species (ROS) than the wild-type strain. In addition, the pst mutant demonstrated reduced expression of genes involved in lipopolysaccharide modifications and coding for cell surface components such as type 1 and F9 fimbriae. Phenotypic tests also established that the pst mutant was impaired in its capacity to produce type 1 fimbriae, as demonstrated by western blotting and agglutination of yeast cells, when compared to wild-type APEC strain χ7122.ConclusionOverall, our data elucidated the effects of a pst mutation on the transcriptional response, and further support the role of the Pho regulon as part of a complex network contributing to phosphate homeostasis, adaptive stress responses, and E. coli virulence.
Highlights
Avian pathogenic E. coli (APEC) are associated with extraintestinal diseases in poultry
Microarray design to identify differentially expressed genes in the APEC pst mutant To assess the effects of a pst mutation as well as Pho regulon activation on APEC strain χ7122, a transcriptional profiling approach was used
The Pho regulon induction reaches its maximal rate at mid-log phase of growth in strain K3 as determined by PhoA activity (200 Miller units (MU)), whereas it was repressed in the wild-type parent strain χ7122 (3 MU)
Summary
Avian pathogenic E. coli (APEC) are associated with extraintestinal diseases in poultry. The global mechanisms contributing to the attenuation and decreased resistance of the APEC pst mutant to environmental stresses have not been investigated at the transcriptional level. To determine the global effect of a pst mutation on gene expression, we compared the transcriptomes of APEC strain χ7122 and its isogenic pst mutant (K3) grown in phosphate-rich medium. The two-component system (TCS) PhoR/PhoB responds to environmental phosphate concentration variations and has been shown to control expression of at least 47 genes [1,2]. The Pst system encodes an ATP-binding cassette (ABC) transporter involved in the transport of Pi. Importantly, mutations in the Pst system result in constitutive expression of the Pho regulon, regardless of environmental phosphate availability, and affect virulence of many pathogenic bacteria [1]
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