1. Microbial Biotechnology
Lecture:2
Microbial Biotechnology

2. Microbes can be classified into four major groups:
1- Viruses Bacteria
3- Fungi Protozoa

3. 1- Viruses

4. Introduction to Viruses
Obligate
Intracellular
Parasite

5. Virion Structure Lipid Envelope Nucleic Acid Protein Capsid Virion
Spike
Projections
Protein
Capsid
Lipid Envelope
Virion
Associated
Polymerase
·         This overhead shows the standard features found in some (but not all) viruses.
·         A virus particle is essentially a piece of nucleic acid surrounded by a protein coat.
·         The protein coat (i.e. the capsid) is a delivery system for transferring the virus genome from one cell to another. The protein serves to:
Ø     Provide protection to the nucleic acid against the environment - e.g. nucleases etc.
Ø     Function in receptor recognition - targeting a virus to a susceptible host and cell type.
·         Surrounding this coat there may be a lipid envelope - this envelope is derived from one of the cell membranes and is not determined by the virus. There may be some modification to the lipid composition induced during virus maturation.
·         Inserted into the lipid envelope there are usually virus proteins which are present as spike projections - these are normally glycoproteins.
Due to restrictions on the coding size of many virus genomes the capsid of the virion is made up of repeating subunits, which coat the virus genomic nucleic acid. The redundancy also allows for the fact that if there is an inactivation of part of the capsid the virus does not completely lose its infectivity For example the poliovirus RNA (7kb) can specific at most 250,000 Daltons of protein altogether (some must be used for replication) but the poliovirus virion capsid weighs 6 x 106 Daltons.
Genomic Nucleic Acid
Viruses only possess a single type of genomic nucleic acid – either DNA or RNA but not both. This nucleic acid can be in a variety of physicla forms that can be used as a valuable classification feature.

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Characteristics
Viral capsids (coats) are made of individual protein subunits
Individual subunits are called capsomeres
CAPSOMERES
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Discovery of Viruses
Beijerinck (1897) coined the Latin name “virus” meaning poison.
He studied filtered plant juices & found they caused healthy plants to become sick.
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8. Tobacco Mosaic Virus
Wendell Stanley (1935) crystallized sap from sick tobacco plants
He discovered viruses were made of nucleic acid and protein

9. Smallpox
Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses
Deadly viruses are said to be virulent
Smallpox has been eradicated in the world today

10. Morphology of viruses

11. Viral Shapes There are 3 different shapes of Virus Helical Icosahedral
(Tobacco mosaic virus)
Complex
(Bacteriophage – a virus which infects bacteria)
Icosahedral
(Influenza)

12. Viral Properties Viruses are inert (nucleoprotein ) filterable Agents.
Viruses cannot make energy or proteins independent of a host cell.
Viral genome are RNA or DNA but not both.
Some viruses contain proteins with enzymatic functions that are needed for genome
They are very small in size, from m.
They are unaffected by antibiotics.
They are sensitive to interferon.

13. Are viruses alive? No Yes They are not made of cells or organelles
They cannot reproduce without a host
They do not metabolize energy
They do not perform cellular processes
Reproduce
They have DNA or RNA
They can adapt to surroundings
The have organization

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Chickenpox Virus
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15. Viruses that attack bacteria are called bacteriophage or just phage
T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails
HOST specific

16. Diagram of T-4 Bacteriophage
Head with 20 triangular surfaces
Capsid contains DNA
Head & tail fibers made of protein