Phage Genetics - BIO 141 Lecture Notes PDF

PHAGE GENETICS Bacteriophages Virus, “deadliest being” Most abundant and widely distributed organisms on earth Discovered by Fredrick William Twort and Felix d'Hérelle (20th Century). Specifically infect bacteria Structure of a phage Head or capsid ○ Contains genetic material (nucleic acid) ○ Shape...

PHAGE GENETICS Bacteriophages Virus, “deadliest being” Most abundant and widely distributed organisms on earth Discovered by Fredrick William Twort and Felix d'Hérelle (20th Century). Specifically infect bacteria Structure of a phage Head or capsid ○ Contains genetic material (nucleic acid) ○ Shape is icosahedral Tail ○ Contractile ○ Injects the nucleic acid to target bacteria Lytic Cycle Attachment ○ Attach tail fibers to host cell Penetration ○ Open cell wall using lysozyme ○ Injects nucleic acid to host Biosynthesis ○ Production of phage DNA and proteins Assembly/Maturation ○ Assembly of phage particles into one complete infectious virus: virion Release ○ Break cell wall to release phage ○ Endolysin e.g. lysozyme ○ Bacteriophages in Microbial Genetics Mainly used as a model to explore the mechanisms of life and led to the birth of modern molecular biology One classical example is the demonstration of a central biological question in the 20s: The Hershey-Chase Experiments (1952) → The Hershey-Chase Experiments (1952): In 1952, Alfred Hershey and Martha Chase conducted a series of experiments to confirm that DNA is the genetic material in living organisms. The experiments involved infecting bacteria with bacteriophages, which are made of DNA and protein, and labeling the protein and DNA with radioactive isotopes. The results showed that the DNA entered the bacterial cell, but most of the protein did not, and that the protein remained attached to the cell membrane. This led Hershey and Chase to conclude that genetic information is DNA, not proteins Lysogenic Cycle Attachment Penetration/Entry Integration ○ Phage DNA recombines with bacterial chromosome ○ Prophage - bacteriophage genome integrated into the host genome Cell Division Phage DNA copied along with bacteria When is it Lytic/lysogenic ○ Phage: host ○ UB ○ Chemicals ○ Spontaneous Considered for development of strategies to treat infections Lagged behind because of the discovery of antibiotics ○ Effective ○ Greater breadth and potency ○ E.g. Penicillin led to mass production However discovery and overuse of antibiotics led to antibiotic resistance and the development of superbugs. Antibiotics: carpet bombing Phages: high specificity; personalized guided missiles. How does antibiotic resistance develop? Do bacteria adapt to phages as well? Bacteriophages Made a comeback Emergence of multi-antibiotic resistant bacteria and low rate of new antibiotic discovery brought the new urgency to develop phage-based therapies. Phage therapies against: E.g. Pseudomonas aeruginosa and Acinetobacter baumannii Applications of Phage Therapies 1. Treatment of bacterial infections and wounds. 2. Skincare products 3. Preventing biofilms on medical devices. 4. Anti-tumor 5. Veterinary medicine