 They are reproduce  Carry on the metabolism  Organize the cell  They contain enzymes, nucleic acids, carbohydrates, lipids  Adapt to changing environments

 They are reproduce, has macromolecules, adapt to changing environment  alive  They are not cells, lack any significant metabolism  not alive

 Host range: spectrum of organism can be attacked by virus  Animal virus, plant virus, bacterial virus (bacteriophages/phages)  Only attack single species  depend on receptor (proteins)

 20 nm nm (1/3-1/10 bacteria) No ribosom, cytoplasm, nucleus Nucleic acid wrapped by protein coat Largest:77 genes – T4(1/50 x E.coli), Smallest: 3 genes

 Composed of protein subunits called capsomeres.  Functions  Protective  Recognition/attachment to host cells  Introduction of nucleic acid into host cell

 Composition  Lipids from host cell membrane  Proteins  Glycoproteins  Function  Recognition/attachment to host cell

 RNA or DNA  Double or single- stranded  Segmented or nonsegmented ds DNAss DNA ss RNA nonsegmented ds RNA segmented

Helical Isometric (cubic)

Complex

 Host range  Very specific  Enveloped or nonenveloped  Type of nucleic acid  Shape

 Viruses that infect bacteria.

 Virulent  Lytic multiplication cycle  Temperate  Lysogenic multiplication cycle

Adsorption Bacteriophage E. coli host bacillus Lytic Cycle

Adsorption Bacteriophage Viral DNA Bacterial DNA E. coli host bacillus Lytic Cycle Penetration

Adsorption Penetration Lytic phase Duplication of phage components; replication of virus genetic material Bacteriophage Viral DNA Bacterial DNA E. coli host bacillus Lytic Cycle

Adsorption Assembly of new virions Penetration Lytic phase Duplication of phage components; replication of virus genetic material Bacteriophage Viral DNA Bacterial DNA Eclipse phase E. coli host bacillus Lytic Cycle

Assembly of new virions Adsorption Maturation Penetration Lytic phase Duplication of phage components; replication of virus genetic material Bacteriophage Viral DNA Bacterial DNA Eclipse phase E. coli host bacillus Lytic Cycle

Assembly of new virions Adsorption Lysis of weakened cell Release of viruses Maturation Penetration Lytic phase Duplication of phage components; replication of virus genetic material Bacteriophage Viral DNA Bacterial DNA Eclipse phase Virion phase E. coli host bacillus Lytic Cycle

Burst size

Lysogenic Cycle lysogen

Prophage

BacteriumDisease Phage encoded property Corynebacterium diphtheriae DiphtheriaDiphtheria toxin Clostridium botulinum BotulismBotulinum toxin Streptococcus pyogenes Scarlet feverErythrogenic toxin

Infect bacteria Mix with molten soft agar Plate plaque

Seven steps in Generalised Transduction 1. A lytic bacteriophage adsorbs to a susceptible bacterium. 2. The bacteriophage genome enters the bacterium. The genome directs the bacterium's metabolic machinery to manufacture bacteriophage components and enzymes 3. Occasionally, a bacteriophage head or capsid assembles around a fragment of donor bacterium's nucleoid or around a plasmid instead of a phage genome by mistake.

Seven steps in Generalised Transduction (cont’d) 4. The bacteriophages are released. 5. The bacteriophage carrying the donor bacterium's DNA adsorbs to a recipient bacterium

Seven steps in Generalised Transduction (contd) sduction/transduction.html 6. The bacteriophage inserts the donor bacterium's DNA it is carrying into the recipient bacterium. 7. The donor bacterium's DNA is exchanged for some of the recipient's DNA.

Six steps in Specialised Transduction 1. A temperate bacteriophage adsorbs to a susceptible bacterium and injects its genome. 2. The bacteriophage inserts its genome into the bacterium's nucleoid to become a prophage.

Six steps in Specialised Transduction (cont’d) 3. Occasionally during spontaneous induction, a small piece of the donor bacterium's DNA is picked up as part of the phage's genome in place of some of the phage DNA which remains in the bacterium's nucleoid. 4. As the bacteriophage replicates, the segment of bacterial DNA replicates as part of the phage's genome. Every phage now carries that segment of bacterial DNA.

Six steps in Specialised Transduction (cont’d) 5. The bacteriophage adsorbs to a recipient bacterium and injects its genome. 6. The bacteriophage genome carrying the donor bacterial DNA inserts into the recipient bacterium's nucleoid.