• Bacteria are primitive organisms consisting of single cells (prokaryotes, without a true nucleus).

• They have no chlorophyll and their body is not differentiated into parts like root,  stem,  leaves, and flowers.

Bacteria - A Central Study:

• Bacteria are the most primitive unicellular organisms.

• Each bacterial cell contains a single chromosome (nuclear material) which is not enclosed in a nuclear membrane.

Bacteria - So Numerous and Everywhere:

• There are several thousand known species of bacteria that occur in air, water,  soil, food-stuffs, on or inside the body of living organisms, and in short, practically everywhere.

• In our own body, there are hundreds and thousands of bacteria in the mouth, on the skin, inside the intestines, in the genital tracts, etc.

  • Some bacteria occurring in our intestines are beneficial, they synthesize certain vitamins, such as vitamin B.

    • Certain bacteria are highly injurious causing diseases, but there are others that are highly beneficial.

      • [According to one estimate, there are more bacteria normally living on your skin than the total number of humans living on Earth.]

      • (These bacteria are even useful as they prevent the growth of harmful ones).

• Size: Bacteria are the smallest living organisms on earth, with an average size of 2 micrometers long and 0-5 micrometers thick (1 micrometer = one-thousandth of a millimeter).

• Shape: Shape-wise, the bacteria are usually of four types:

  • Cocci (spherical bacteria),

  • Bacilli (rod-shaped bacteria),

  • Spirilla (spiral or twisted bacteria),

  • Vibrio (comma-shaped).

  • Many bacteria live single but some occur in pairs (diplococci), in long chains (streptococci), or in clusters (staphylococci).

• Structure: Each individual bacterium is rather a simple cell.

  • It contains the living substance protoplasm/ protoplast lying within the cell membrane (cytoplasm + bacterial chromosome) surrounded by a non-living stiff cell wall.

  • The cell wall is made of peptidoglycan and not of cellulose (as in plant cells).

  • A thin cell membrane lies immediately beneath the cell wall arid that surrounds the cytoplasm.

  • There is no well-defined nucleus but chromatic (DNA) material is present in the central region.

    • This chromatic material is in the form of a single circle and is not enclosed in a nuclear membrane, but is attached to the cell membrane at some point.

    • The cytoplasm contains vacuoles, granules, and, in very few cases, some green pigment as well.

    • Sometimes a slimy protective layer called a capsule is present outside the cell wall.

• Movement: Most bacteria cannot move about by their own effort and they are only passively transported by wind, water, or contact.

  • But some bacteria possess one or more whip-like flagella which pierce through the cell wall and capsule.

  • The lashing movements of the flagella provide active locomotion in a liquid environment.

• Nutrition: Most bacteria have no chlorophyll, therefore, they depend on readymade food from different sources (heterotrophic).

  • In this category, the bacteria may be:

    • saprotrophic (drawing nourishment from decaying dead organisms), or

    • parasitic (drawing nourishment from the body of their living hosts).

  • The bacteria secrete powerful enzymes from their cells into the surrounding food-containing material.

  • The enzymes make the food material soluble which is then absorbed as a solution into the bacterial cell.

• Respiration: Some bacteria respire by absorbing atmospheric oxygen (aerobic), and others need no free oxygen (anaerobic).

  • The anaerobic bacteria are killed if exposed to air.

• Reproduction: Reproduction in bacteria is only asexual by means of fission or cell division.

  • The circular DNA duplicates.

  • The cell expands and the two DNA are pulled apart.

  • The cell constricts in the middle separating the two cells.

    • Depending on the type of bacteria the two daughter cells may either remain attached or may separate from each other as independent cells.

• A highly primitive type of sexual reproduction has been found in very few bacteria and is extremely simple.

  • In this method, two bacteria of different strains (but of the same species) come together (conjugation).

  • The plasmid of the donor may be transferred into the recipient through a hollow tubelike extension of the donor cell.

• Spores to overcome in anaerobic conditions.

  • When unfavorable conditions set in, such as the drying up of vegetation, the bacterial cell draws its content into a spherical mass which becomes surrounded by a thick and hard protective wall.

  • This little rounded body is a spore that is contained within the original cell wall but later becomes free when the cell wall ruptures.

  • Such spores are usually in the resting stages which can withstand unfavorable conditions.

    • These can tolerate extreme dryness.

    • Some cannot be killed even at the temperatures of boiling water or frozen ice.

    • Some can tolerate poisonous chemicals.

  • The spores can be carried far and wide by various means such as wind, water, or contact.

  • On meeting favorable conditions the spores germinate, and their dormant protoplasm becomes active and streams out of the ruptured wall in the form of a new bacterium.

Antibiotics:

• An antibiotic is a chemical substance produced by living organisms that can stop the growth of disease-producing bacteria and fungi.

  • Examples: streptomycin, chloromycetin tetracycline, and penicillin.

• Penicillin: The first produced antibiotic (from a fungus and not a bacterium).

  • In 1929 Alexander Fleming observed that sorry bacteria growing in culture were destroyed by accidental contamination of a mold Penicillium notatum.

    • He discovered that this mold produced a substance that suppressed the growth of many bacteria and the substance was named penicillin, the first antibiotic for medical use.

Criteria for a good antibiotic:

• It should be able to kill a variety of disease-producing microorganisms (“broad spectrum” antibiotics).

• It should not produce undesirable side effects.

• It should not kill normal bacteria in the host.

Other Uses of Antibiotics:

• As food preservatives, especially for fresh meat and fish.

• For treating animal feed.

• For controlling plant pathogens.

Serum:

• Serums contain antitoxins (chemical substances) of a particular pathogen.

  • Serums are used as a preventive measure against bacterial invasion.

  • For preparing serum, a small dose of bacterial toxin is introduced into the blood of a healthy animal such as a horse or cow.

• The body produces antitoxins to neutralize the effect of toxins.

  • After several injections of the same toxin the blood of such an animal is taken out.

    • On chilling, it clears as a straw color liquid that separates out from the clot and is called serum.

    • Snake-bite treatment involves injecting the particular anti-venom produced from the blood of horses, etc.

    • Genetic engineering has made it possible to introduce human genes in certain bacteria like Escherichia coli (E. coli).

      • These bacterial cultures grow very rapidly.

      • The particular gene-dependent products are extracted from these bacteria.

        • The hormone insulin was the first such substance produced by E. coli.

• A few serum compounds produced genetically are:

  • Blood clotting factor VIII for the treatment of Haemophilia A.

  • Factor IX for the treatment of Haemophilia B.

Vaccines:

• Introduction of weakened germs or dead germ substances into the body for development.

  • Vaccines are available for a variety of diseases such as cholera, typhoid, measles, chickenpox, etc.

    • On injecting them into the body the person gets the disease in mild form and his body gets stimulated to produce antitoxins.

    • The antitoxins provide immunity against any future attack of the particular disease germs.

• Two common vaccines obtained by growing bacteria:

  • Killed bacteria: for TAB vaccine for typhoid.

  • Living weakened bacteria: for BCG vaccine for tuberculosis.

Toxoids:

• Toxoids are the inactivated toxins of the particular bacteria, which can still stimulate the production of the respective antibodies such as those for producing immunity against diphtheria and tetanus.

Bacteria - Role in Agriculture:

• A special category of soil bacteria (Rhizobium) is found living in small nodules on the roots of leguminous plants such as beans.

  • These bacteria pick up free nitrogen from the soil atmosphere and convert it into soluble nitrates.

    • These nitrates are used by the host plant and also by other plants sown later in the same soil.

• Certain free-living bacteria in the soil like Azotobacter, Clostridium, etc. use the free nitrogen of the soil and convert it to ammonia with hydrogen which in turn gets converted to amino acids and nitrates, enriching the soil.

  • Plants need nitrogen for synthesizing proteins, but they cannot make use of the free atmospheric nitrogen.

    • They can obtain it only in the form of nitrates, which they absorb from the soil through roots.

    • These nitrates are replenished in the soil by bacteria through the process of nitrification.

• Denitrifying Bacteria are the bacteria present in the soil, which break down the soil nitrates to release nitrogen gas (N2) that enters the atmosphere.

Bacteria: Role in Industry:

• Bacteria have very extensive use in industry.

  • You have already read about their role in producing certain types of medicines on a large scale.

• Here are two more out of several other uses:

  • Different varieties of tea are produced by certain bacteria (this is termed tea curing).

  • Leather Tanning is primarily brought about by sunlight but certain bacteria break down the soft perishable parts of the skin (hide).

Spoilage of Food by Bacteria:

• Many bacteria spoil cooked food, milk, and fruit. vegetables, etc, by the process of decay (fermentation) particularly during summer.

  • This spoilage may sometimes to the extent of causing food poisoning.

    • Botulism is a very serious food poisoning due to a special bacterium sometimes found in tinned and sealed foods (the affected cans get distended at their ends with gas which gushes out on opening — such suspected foods should be completely discarded.

• Therefore, the preservation of food is very necessary.

  • Food preservation can be brought about by several methods:

    • Boiling or heating at high temperatures (Sterilization):

      • Boiling water kills all bacteria except their spores.

        • Higher temperatures (about 110° C) at increased pressure (as in an autoclave, or in a pressure- cooker) kill even the spores.

        • The eating industry employs heating to kill bacteria before packing and sealing food

    • Salting:

      • Salting is a common method of preserving foods like fish, pickles, etc., for long periods of time.

      • By mixing these foods with salt their bio-degradation is prevented under normal conditions.

      • Treatment with salt for preservation purposes is called curing.

    • Dehydration (Drying):

      • Most microbes cannot grow without water.

      • Therefore, dehydration by drying foods such as grains, meat, fish, and vegetables is an effective method of preservation.

      • Dried milk powder is another excellent example.

    • Irradiation:

      • Radioactive radiation has been tried in sterilizing certain foods without themselves becoming radioactive, but the practice is not yet in much use.

      • Similarly, ultra-violet light is found useful, not only in sterilizing the air in schools, hospitals, and factories but also in killing mold spores in bakeries.

    • Pasteurization:

      • Pasteurization is a technique of partial sterilization applied usually to milk.

      • The milk is heated to a temperature of about 60°C for a period of 30 minutes and then chilled quickly.

      • Pasteurization kills a majority of the bacteria that are present, including the disease-causing ones.

      • Remember, pasteurization does not completely sterilize milk.

      • Souring bacteria may still be present in it, but by keeping the milk sufficiently cool, they do not multiply.

    • Refrigeration (cold temperature):

      • Microbes (bacteria and molds) do not grow and multiply at or below the freezing point of water.

      • Chilling milk and keeping vegetables and fruit in cold storage are popular methods of preserving them.

      • Frozen fish or frozen vegetables keep fresh for a long time.

      • Domestic refrigerator cools at 0 - 5°C for short-term storage.

      • Deep freezing cools at —20°C to —30°C for long-term storage.

    • Strong concentration and chemicals:

      • Jams and pickles do not get spoiled.

      • They have a strong concentration of sugar and salt respectively.

      • The increased concentration of the solutes causes plasmolysis and death of any bacteria, or mold that may creep in.

      • Sometimes preservatives like sodium benzoate are also added to tinned foods and squashes.

Bacterial Diseases in Plants and Animals:

• In Plants:

  • Two very common diseases of plants caused by bacteria are the black rot of mustard and cauliflower and the bacterial blight of cowpea (“lobia”).

• In Animals:

  • Two common bacterial diseases of cattle among

    animals are:

    • Anthrax: Swelling on the body and reduced milk

      yield.

    • Tuberculosis: Lungs affected, dry husky cough.

• In Humans:

  • Some common bacterial diseases in humans are whooping cough, cholera, tuberculosis, diphtheria, typhoid, pneumonia, and tetanus.

Bioweapons:

• It has come to a knowledge that some countries may be preparing ‘germ bombs’ which when exploded may simply release disease germs such as Anthrax bacteria which may take epidemic shape and cause widespread death generation after generation.