Phage defence systems

• Phages outnumber bacteria by 1:10
• Phage head hold the genome
• Phage tail has a tube and a baseplate
• The phage tail guides the genome into the bacteria
• The phage baseplate contains sensors which recognise bacteria
• Bacterial DNA can be dsDNA ssDNA or RNA
• Lytic infections lead to reproduction of phages within the bacteria and then lysis of bacteria
• Lysogenic phages incorporate their DNA into the host
• Lysogenic phages can reenter the lytic cycle
• Prophages carry out horizontal gene transfer to give th ebacteria survival traits
• Phages can transfer immunity, defence systems, quorum sensors or virulence factors
• Lytic phages present clear plaques as they have killed the phages
• Lysogenic phages produce turbid plaques as some bacteria remain for phage survival
• Bacteria can mutate their phage binding receptor
• Bacteria have restriction enzymes which cut specific sequences of phage DNA
• Host DNA is protected from restriction enzymes as they are methylated
• CRISPR-Cas is a system which recognises previously encountered phages
• Cas enzymes cut the protospaces sections of phage DNA
• These phage protospages are stored within CRISPR DNA
• CRISPR RNA can bid to phage effectors which destroy invaders
• Phages can have anti CRISPR proteins which prevent effector binding
• Gabija defence aims to detect changes in phage nucleotides
• As phages assemble there will be a decrease in the amount of nucleotides
• The decrease in nucleotides activates the Gabija complex
• Gaj A detects the change in nucleotides
• Gaj B DAase destroys the phage
• Gabija detection leads to metabolic arrest and bacterial lysis
• PARIS is phages anti-defence system
• OcR protein mimics DNA and targets the restrictions enzymes
• AriA inhibits the restriction enzymes
• AriB will mimic DNA and preventing Restriction enzymes trageting DNA