Tobacco mosaic virus (TMV)

TMV was the first virus to be discovered by the Dimitri Ivanowski in 1892 and crystallized by the W.M Stanley. It causes mosaic disease in tobacco plant. It belongs to tobamo virus group.

It is rod shaped, containing no envelope measuring about 300nm in length and 15-17 nm in diameter.

It has a protein capsid constituting of 95% of virus and a core of nucleic acid. The capsid is in the form of a tube with a cavity measuring about 2nm in diameter. It is composed of 2130 identical capsomers which are closely packed and arranged in the form of a regular spiral or helix.

There are about 49 capsomers for every 3 turns that is about 16 per turn of the helix. There are 130 turns in a complete virus capsid.

Microsystis

Kingdom: Monera

Division: Cynophysia

Class: Cynophyceae

Order: Chrococcales

Family: Chrococcaceae

Genus: Microsystis


Microsystis is a free floating or planktonic blue green algae commonly found in fresh water bodies such as ponds pools lakes, etc. which maybe contaminated by sewage water. It generally forms dense water grooms. It is colonial form and the colonies are irregular. Each colony consists of a large number of densely packed small cells that are evenly distributed through out a common thin watery, gelatinous matrix. On mucilaginous matrix which is colourless and homogenous. The colony has many air space also called pseudo vacuoles or gas vacuoles which gives bouncy and allows the algae to float on the surface of water. The gas vacuole also helps in exchange of gases.


The cells are usually spherical. Each cell is typically cyanophychian with a central colourless incipient nucleus (centroplasm) and a peripheral highly pigmented chromoplasm. The chromoplasm contains phycocyanin (blue pigments), chlorophyll (green pigments) in large amounts and phycoerythrin (red pigments) in small amounts. The centroplasm consists of naked DNA without a nuclear membrane.

REPRODUCTION

It is by cell division of cells along the three planes. Sometimes a few cells may separate from the colony and develop into a new colony

ECONOMIC IMPORTANCE

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  • Microsystis is known to cause to form water blooms and there for deprives the aquatic animals of the oxygen by preventing exchange of gas between the water and the atmosphere.
  • It produces neurotoxin which causes nerve disorder in animals consuming water contaminated with microsystis. swimming in water with microsystis causes skin irritation and diseases
  • Since microsystis grows abundantly in polluted water, it is used as a biological indicator for water pollution.

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Economic importance of genus Aspergillus.

Aspergillus has both harmful ans useful activities from the view of the human.

Harmful activities

Many species of Aspergillus such as A. glqaus A.flavus A. repns are responsible
of spoilage of exposed food stuff like jams, jellies, bread, tobacco and
many other product like leather & textiles. Many of the species are pathogenic to animals as well as human beigns. A. flavus,

A. fumigates and A.niger causes diseases of respiratory tracks commonly refered to as
aspergilloses. Aspergilloses is reported in birds, cattle, sheep, horses and human begins.

Symptoms of Aspergillosis resembles those of tuberculosis. Diesease of the human ear called otomycosis is caused by A.niger, A.flavus and A.fumigatus.

A.flavus produces a toxic substance called afflotoxin which has some carcinogenic effects and may cause cancer of liver in human begin and animals.


Conidia of Aspergillus are abundant in air. They usually spoil the laboratory culture. Many plant diseases-crown rot of ground nut and ball rot of cotton are caused by
species of Aspergillus.


Aspergillus nidulaus


A. niger

Useful effects

Several species are employed in cheese manufacturing.

A.oryzae is used in the preparation of wine from rice and soya bean sauces. Some specises of aspergillus are the source of certain antibiotics like Flavicein,Aspergillin, Geodin, Funagalin, Patulin, Ustin etc.

A. niger is used in bio-assay of metals as it can detect copper even in traces.

A.gowssipii is used in the production of vitamin B. Some species are used in the production of fats. Several species are used in the industrial production of organic acids like citric acid and gluconic acid.

 
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