Structure of Bacterial Viruses

Virology

1. Virology lab 3 The Structure Of Bacterial Viruses Using Electron Micrograph T. Amani Alsharidah

2. Bacteriophages Bacteriophage, also called phage or bacterial virus , any of a group of viruses that infect bacteria. Bacteriophage means “bacteria eater”. Thousands of varieties of phages exist, each of which may infect only one type or a few types of bacteria. Phages are classified in a number of virus families ; some examples include Inoviridae , Microviridae , Rudiviridae , and Tectiviridae . phages are simple organisms that consist of a core of genetic material (nucleic acid) surrounded by a protein capsid . The nucleic acid may be either DNA or RNA and may be double-stranded or single-stranded. Two life cycles , lytic (virulent) or lysogenic (temperate).

3. Bacteriophage Structure

4. Types of Phages There are three basic structural forms of phage: An icosahedral (20-sided) head with a tail An icosahedral head without a tail. A filamentous form.

5. 1- Lambda phage ( λ ) A temperate bacteriophage, an obligate parasite. It belongs to the family of lambdoid phages , that includes phages ϕ21, ϕ80, ϕ81, etc. Lambdoid phages are characterized by cohesive ends , the ability to recombine, and inducibility by UV. Each λ particle contains in its icosahedral head (0.05 μm in diameter) one double-stranded DNA molecule of ca. 49,502 bp In its E. coli host it can replicate either and produce hundred progeny particles in 50 min at 37°C. Alternatively, it may insert into the host chromosome as a prophage.

6. Electron micrograph of Lambda Phage λ

7. 2- T4 phage Bacteriophage T4 is one of the seven Escherichia coli phages (T1–T7), T for type. Bacteriophage T4 is classified as a member in the Myoviridae family, because it has a contractile tail. It has highly symmetrical heads, tails and baseplates. It has dsDNA genome of 168 Bp. The contractile tail improves the efficiency of infection by making it possible for the tail tube to penetrate the outer host cell membrane prior to the delivery of phage DNA into the host cell.

8. T4 Phage Structure Capsid (head): polyhedral and the tail sheath is helical. The tail has an inner hollow tube called core, surrounded by a contractile sheath which consist of 24 annular rings. The distal end of the tube is connected to a hexagonal basal plate with spike or tail spin at each corner. Six long, flexible tail fibers also arise from the basal plate.

9. Electron micrograph of T4

10. 3-Bacteriophage phiX174 ( ɸX174) Bacteriophage phiX174 hijacks bacterial cells and forces them to make new copies of the virus. PhiX174 is composed of a single circle of DNA 5386 Bp surrounded by the icosahedral protein. Sixty copies of the capsid protein form a spherical shell around the DNA.

11. Electron micrograph of phX174