VIRUSES

ALIVE? They are reproduce Carry on the metabolism Organize the cell They contain enzymes, nucleic acids,

carbohydrates, lipids Adapt to changing environments

HOW ABOUT VIRUS? 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)

SIZE

20 nm - 300 nm (1/3-1/10 bacteria)

No ribosom, cytoplasm, nucleusNucleic acid wrapped by protein coatLargest:77 genes – T4(1/50 x E.coli), Smallest: 3 genes

VIRAL STRUCTURE

CAPSIDS

Composed of protein subunits called capsomeres.

Functions Protective

Recognition/attachment to host cells

Introduction of nucleic acid into host cell

ENVELOPES

CompositionLipids from host cell

membraneProteinsGlycoproteins

FunctionRecognition/

attachment to host cell

GENOME

RNA or DNA

Double or single-stranded

Segmented or nonsegmented

ds DNA ss DNA

ss RNA nonsegmented

ds RNA segmented

VIRAL SHAPE

Helical

Isometric (cubic)

VIRAL SHAPE

Complex

CLASSIFICATION OF VIRUSES

Host rangeVery specific

Enveloped or nonenveloped

Type of nucleic acid

Shape

BACTERIOPHAGE Viruses that infect bacteria.

TYPES OF BACTERIOPHAGE Virulent

Lytic multiplication cycle

TemperateLysogenic multiplication cycle

Adsorption

BacteriophageE. coli host bacillus Lytic Cycle

Adsorption

Bacteriophage

ViralDNA

BacterialDNA

E. coli host bacillus Lytic Cycle

Penetration

Adsorption

Penetration

Lyticphase

Duplication of phage components;replication of virus

genetic material

Bacteriophage

ViralDNA

BacterialDNA

E. coli host bacillus Lytic Cycle

Adsorption

Assembly ofnew virions

Penetration

Lyticphase

Duplication of phage components;replication of virus

genetic material

Bacteriophage

ViralDNA

BacterialDNA

Eclipse phase

E. coli host bacillus Lytic Cycle

Assembly ofnew virions

Adsorption

Maturation

Penetration

Lyticphase

Duplication of phage components;replication of virus

genetic material

Bacteriophage

ViralDNA

BacterialDNA

Eclipse phase

E. coli host bacillus Lytic Cycle

Assembly ofnew virions

Adsorption

Lysis of weakened cell

Release of viruses

Maturation

Penetration

Lyticphase

Duplication of phage components;replication of virus

genetic material

Bacteriophage

ViralDNA

BacterialDNA

Eclipse phase

Virion phase

E. coli host bacillus Lytic Cycle

LYSIS

http://www.oranim.ac.il/courses/microbiology/phagelab.htm

Burst size

Lysogenic Cycle

lysogen

LYSOGENIC STATE

Prophage

PHAGE LIFE CYCLE CHOICES

LYSOGENIC CONVERSION

Bacterium Disease Phage encoded property

Corynebacterium diphtheriae Diphtheria Diphtheria toxin

Clostridium botulinum Botulism Botulinum toxin

Streptococcus pyogenes Scarlet fever Erythrogenic toxin

PROPAGATION OF BACTERIOPHAGE

Infect bacteria Mix with molten soft agar

Plate

plaque

DETERMINING TITER

http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap9.html

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)

http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/transduction/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.

http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/transduction/spectran.html