Bacteriophages are viruses that infect bacteria. Many types of bacteriophage exist, some simply infect and lyse their host bacteria, while others insert into the bacterial chromosome. A bacteriophage can contain genes that contribute to its host's phenotype: for example, in the evolution of Escherichia coli O157:H7 and Clostridium botulinum, the toxin genes in an integrated phage converted a harmless ancestral bacterium into a lethal pathogen. Bacteria resist phage infection through restriction modification systems that degrade foreign DNA, and a system that uses CRISPR sequences to retain fragments of the genomes of phage that the bacteria have come into contact with in the past, which allows them to block virus replication through a form of RNA interference. This CRISPR system provides bacteria with acquired immunity to infection. COUNT 4
QSN1 What are Bacteriophages? ANS1 viruses that infect bacteria QSN2 What can viruses do to bacteria? ANS2 infect and lyse their host bacteria QSN3 What can happen if Bacteriophage contain genes of host's phenotype? ANS3 lethal pathogen QSN4 How can bacteria resist virus DNA? ANS4 CRISPR system provides bacteria with acquired immunity