Harmful and Useful Activities of Bacteria | Botany

In this article we will discuss about the harmful and useful activities of bacteria.

Harmful Activities:

Some bacteria are harm­ful to human affairs in different ways:

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 is given below (Table 2.6-2.8 and 2.11).

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 N₂ through dissimilatory nitrate reduction.

The two pathways have a common inter­mediate, the nitric oxide:

The free nitrogen goes to the atmosphere, resulting in the reduction of soil fertility by loo­sing valuable N₂ source, the nitrate. The bacteria those cause denitrification are called denitri­fying bacteria, e.g., Bacillus cereus, Paracoccus denitrificans, and Pseudomonas aeruginosa.

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.

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.

These bacteria are of the following three categories:

(i) Nitrifying bacteria:

This group of bacteria oxidises ammonia to nitrate in two steps. The first step involves the oxidation of ammonia to nitrous acid by bacteria like Nitrosomonas, etc. and the second step involves oxidation of nitrous acid to nitric acid by Nitrobacter.

Step I : NH₃ + 1½O₂———> HNO₂ + H₂O + Energy

Step II : 2HNO₂ + O₂———— > 2HNO₃ + Energy

(ii) Ammonifying bacteria:

Some saprophytic bacteria hydrolyse the proteins of dead animals and plants into amino acids and other organic nitrogenous substances. Some ammonifying bacteria like Bacillus ramosus, Proteus vulgaris, Clostri­dium sp. etc., convert amino acids into ammonia, which combines with water and carbon dioxide to form ammonium carbonate, used by many crops as nitrogen source.

(iii) Nitrogen fixing bacteria:

These bac­teria can fix atmospheric nitrogen.

They are of two types:

(a) Symbio­tic nitrogen fixers like Rhizobium, found in the root nodules of legu­minous plants which fix N₂ about 100-400 kg/hectare/year. The fila­mentous Actinomycete, Frankia found in root nodules of Alnus rugosa can fix N₂ about 150 kg/ hectare/year,

(b) Free-living fixers like Clostridium and Azotobacter can fix N₂ 25-50 kg/hectare/year.

b. Industrial Importance:

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

Some of the uses are:

(i) Dairy industry:

The lactic acid bac­teria are used in the preparation of butter, cheese, curd etc. The curd is prepared from milk by bacteria in two steps. They convert lactose sugar to glucose and then glucose to lactic acid, which sours the milk and coagulates the milk protein (casein) forming curd. Some bacte­ria used in dairy are Lactobacillus plantarum, L. acidophilus, L. bulgaricus, Streptococcus lactis, S. ther­mophilic etc.

(ii) Vinegar industry:

Clostridium aceto- butylicum and Acetobacter aceti, the acetic acid bacteria are used in the conversion of alcohol to acetic acid, the vinegar. This was done in wooden vats and takes several weeks to complete the process.

(iii) Butanol and acetone production:

Butanol and acetone are produced by the action of species of Clostridium on molasses. They are used as solvent in different industry.

(iv) Fibre retting:

Butyric acid bacteria such as Clostridium tetani, C. botulinum etc., are used in the ret­ting of jute, hemp and flax fibres, thereby the bast-fibres become loosen and can be extracted easily.

(v) Curing of tea and tobacco:

The curing of tea and tobacco is done by some bacteria which give parti­cular taste, flavour or smell.

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.

(i) Sources of antibiotic:

Antibiotics are the chemical substances secreted by microorganisms, which inhibit the growth and development of other microorganisms. Antibiotics like bacitracin, polymyxin B, terramycin, streptomycin etc., are of bacterial origin (Table 2.10).

(ii) Serum and vaccine:

Sera (sing, serum) are used by men as thera­peutic measure before infection or after development of diseases like pneumonia, diphtheria etc. Vaccines are commonly used for immunisa­tion against diseases like cholera, typhoid etc.

(iii) Production of vitamins:

Some bacte­ria produce vitamins of commercial importance. Pseudomonas denitrificans is used to produce Cobalamin (Vitamin B₁₂) and Clostridium butylicum is used in the production of Riboflavin (Vitamin B₂).

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.