Transcript C. jejuni
Phase variation in Campylobacter jejuni Recap: genes and proteins 1 codon = 1 amino acid G A G A C T C T C T G A C U C U G A T A C A T G A U G DNA RNA Proteins RECAP: IMMUNITY • Molecules on the surface of bacteria are called antigens B cells RECAP: IMMUNITY • Molecules on the surface of bacteria are called antigens • Cells of the immune system recognise antigens and produce antibodies • Antibodies bind to the bacteria’s antigen and kill them B cells Gastroenteritis- food poisoning • An infection of the gut ▫ Vomitting ▫ Diarrhea • Campylobacter jejuni is the major cause of food poisoning world wide • In rare cases (1/5000) C. jejuni gastroenteritis can progress to the auto-immune disease Guillain-Barre syndrome ▫ Fatal in 2-3% of cases! Campylobacter jejuni C. jejuni lives in the guts poultry without causing disease. Eating uncooked chicken allows C. jejuni into the guts of humans where they can cause disease. C. jejuni has several characteristics that adapt it to cause disease Falsely coloured electro-microscopy image of Campylobacter jejuni How does C. jejuni cause disease? Surface proteins that allow the bacteria to stick to cells in the human gut Flagella- a tail-like structure that helps the bacteria to move through the gut towards nutrients What do they have in common? Expression of them both can be switched ON or OFF reversibly This process is called phase variation. Phase variation = switching genes ON or OFF. Caused by reversible mutation On Mutation Off What does phase variation look like? One cell will divide into two daughter cells With every division, there is a chance they will mutate (mutation rate) Mutation is random. Like rolling a dice This mutation will be passed down to the daughter cells What does phase variation look like? What does phase variation look like? It is a reversible process What does phase variation look like? Many bacteria have more than one phase variable gene Both genes can mutate at the same time Mutation isn’t this quick in real bacteria. What is the effect of phase variation on populations of cells? All of the different cells have the same DNA but have different antigens expressed. How does phase variation happen? -Slippery DNA How can phase variation benefit bacteria? How can phase variation benefit bacteria? Switching some genes off can help the bacteria to escape the immune system. Phase variation of the flagella in C. jejuni is a key factor in the bacteria’s ability to cause disease. Summary • Phase variation is the reversible switching on or off of gene expression • Phase variation is caused by mutations in hyper-mutatable DNA sequences • C. jejuni has many different phase variable genes, some of which are involved in disease.