Question

3. Write short notes
A. Useful and harmful bacteria.​

Answer 1

Answer:

Quick Answer. Examples of helpful bacteria are E. Coli (when used for the digestion process), Streptomyces, and Rhizobium. Examples of harmful bacteria are E. Coli (when contaminating food), Listeriosis, and Salmonella.

Explanation:

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Answer 2

Answer:

Harmful Activities:

a. Pathogenic Bacteria:

These bacteria cause great losses to plant and animal popula­tion by causing several diseases. Some important bacterial diseases of plants and animals, including human beings.

b. Reduction of Soil Fertility:

Some facul­tative anaerobic bacteria are available mostly in the oxygen deficient soil which reverse the nitrifying process, thereby causing the loss of a part of its combined nitrogen. They break down the nitrates in a stepwise manner either to ammonia through assimilatory nitrate reduction or to N2through dissimilatory nitrate reduction.

c. Spoilage of Food:

In favourable temperature and humidity, bacteria can grow luxuriantly in many food materials. They change the flavour, appearance and smell of food.

Different species of Streptococcus, Micro­coccus and Lactobacillus cause spoilage of milk and different milk products. The exotoxin pro­duced by Clostridium botulinum causes botulism disease showing the symptoms like swelling of tongue, double vision and respiratory distur­bances.

d. Pollution of Water:

Some bacteria pol­lute water and make it unsuitable for drinking. Diseases like cholera (Vibrio cholerae), typhoid fever (Salmonella typhi) and bacillus dysentery (Shigella dysenteriae) are commonly transmitted by drinking water.

e. Abortion:

Some species of Salmonella cause abortion of sheep, horse, goat and other animals.

f. Biological Warfare:

Bacteria causing dis­eases like anthrax, black-leg, tuberculo­sis, etc., are used as secret war-agents.

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Useful Activities:

a. Increase Soil Fertility:

Plants do not have the efficiency of direct utilisation of huge amount (78%) of atmospheric nitrogen. However, some free-living and symbiotic bacteria are able to fix free nitrogen into nitrogenous compounds.

b. Industrial Importance:

From ancient time men have used microorganisms in the preparation of their food, drinks etc.

c. Biological Control of Insect:

Many bacteria like Bacillus thuringiensis etc., secrete proteins which are highly toxic to caterpillars and insects belonging to Lepidoptera. They are, however, non­toxic to other animals and also plants, thereby the bacteria are used as ideal agent for biocontrol of insect.

d. Degradation of Petroleum:

Many bacte­ria like Pseudomonas, Micrococcus, Candida and Achromobacter are able to degrade petroleum hydrocarbon in water from different vehicles, thereby they check pollution.

e. Decomposition of Dead Animals:

Some bacteria are, able to decompose the dead organic matters into inorganic form which mix with soil and increase the soil fertility. These inorganic sub­stances are then absorbed by the plants as nutrients.

f. Bacteria in Medicine:

Bacteria are the sources of different antibiotics and they are also used as serum and vaccine.

g. In Sewage Work:

Putrifying bacteria are used to remove the solid and semi-solid constituent of sewage under anaerobic conditions. After treatment the constitu­ents get decayed and liquefied. Those are filtered and the liquid is drained out in the river.

h. Preservation of Green Fodder:

Some bac­teria are used in the preservation of green fodder in pits by the ensilage process.

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