MIC 360 Lecture Notes - Lecture 23: Spi1, Gene Knockout, Pathogenicity Island
Monday, April 16, 2018
MIC 360 Class 23 Notes
1. Salmonella Pathogenicity Island (SPI) I!
-Dna region present in pathogenic bacteria but absent in counterpart bacteria =
implicates something important in the bacteria in the host system environment!
-Can always test whether this region actually functions during the bacteria infection!
-Can knockout region!
-Don’t have to remove entire region - change on gene and then check another and
another!
-Find some components in the island play a major role and others a partial role!
-SPI 1 encodes TTSS!
2. Regulation of TTSS expression SPI-1!
-sensor can respond to the change in the host environment!
-When this Salmonalle is located in the gut lumen, where inside the lumen = high
[Mg2+]!
-High magnesium concentration can turn off the regulatory system!
-Sometimes “turn off regulatory system” doesn’t mean particular gene can be
turned off!
-Instead, some genes whose transcription which is repressed by the SPI-1
regulator can be now activated!
-When the system is turned off, the transcription of those genes will be activated!
-Look at the genes encoded by SPI-1, genes are mostly repressed!
-When the system is turned off, the genes are turned on/activated!
-Pictured on right side of slide = epithelial cell!
-SPI-1 is facing the gut lumen with high magnesium concentration!
-Genes from SPI-1 will be all turned on!
#1
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Monday, April 16, 2018
-When genes are turned on, then it’s going to express on TTSS encoded by
SPI-1!
-This system can penetrate the host cell membrane and therefore inject effectors
into the host cell!
-The function of these factors is to let the host cell take the bacteria into the host
cell!
-SPI-1 is only activated with the magnesium is high in the gut lumen!
-As long as the bacteria cell is outside the host cell, SPI-1 gene will be activated,
and the TTSS encoded by SPI-1!
-Can keep injecting the bacterial proteins into the host cell!
3. SPI II is essential for intracellular survival!
-another island pictured!
-Top = E.coli genome - ydhE!
-Both e coli and salmonella have the ydhE gene!
-On the other side = pykF gene!
-These two genes are not next to each other!
-There’s just a few genes located in between!
-In salmonella genome = big chunk of DNA in red circle with 33 kb = huge!
-This region is the “salmonella pathogenicity island 2”!
-It is the presence of this 33 kb area that confers the virulence in Salmonella!
-Can knockout genes in there and compare the wild type salmonella and
compare with the mutant to compare virulence!
-It’s present in salmonella but not in the E. coli, e. coli is commensal so it does
not have pathogenicity which is why the difference with the large 33 kb
sequence is a “red flag”!
-Why do they need two islands?!
#2
find more resources at oneclass.com
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Document Summary
Mic 360 class 23 notes: salmonella pathogenicity island (spi) i. Dna region present in pathogenic bacteria but absent in counterpart bacteria = implicates something important in the bacteria in the host system environment. Can always test whether this region actually functions during the bacteria infection. Don"t have to remove entire region - change on gene and then check another and another. Find some components in the island play a major role and others a partial role. Spi 1 encodes ttss: regulation of ttss expression spi-1. Sensor can respond to the change in the host environment. When this salmonalle is located in the gut lumen, where inside the lumen = high. High magnesium concentration can turn o the regulatory system. Sometimes turn o regulatory system doesn"t mean particular gene can be turned o . Instead, some genes whose transcription which is repressed by the spi-1 regulator can be now activated.
