Among living organisms, microorganisms are the third domain of classification. This domain includes every unicellular microbe including bacteria, protozoa, viruses and so on. Bacteria are microscopic, single-celled organisms. They have a long-term mutual relationship with humans which are somewhat complex.
Structure of a Bacteria
Bacteria are known for their simple body design. They are single-celled microorganisms with the absence of the nucleus and other cell organelles. They are prokaryotic organisms which are present almost everywhere around us from soil to human guts. Some are extremophiles which live in extreme hot or cold conditions or other harsh conditions.
Another fascinating feature of bacteria is their protective cell wall which is made up of a special protein called peptidoglycan. But few of them are devoid of this cell wall while some have a third protection layer called capsule. On the outer layer, one or more flagella or pili is attached which functions as a locomotory organ as well as attaching part. They do not contain any cell organelle as in animal or plant cell except ribosomes. Ribosomes are the site for synthesis of proteins. Although they possess DNA, it floats within the cell and its region where DNA is present and is called as the nucleoid. In addition to this DNA, they have an extra circular DNA called plasmid. These plasmids make some strains of bacteria antibiotic resistant.
Classification of Bacteria
Bacteria are grouped into five groups based on their shapes such as rod-shaped bacilli, spherical, cocci, spiral-shaped spirilla, and corkscrew spirochaetes. They may either be in clusters or chains or pairs or single. Another criterion for classification of bacteria is by using staining techniques. For e.g. Gram-positive and Gram-negative bacteria.
Reproduction of Bacteria
Bacteria follow the asexual mode of reproduction called binary fission. A single bacterium divides to give two daughter cells. These are identical to the parent cell as well as to each other. Replication of DNA within parent bacterium marks the beginning of the fission. Eventually, cell elongates to form two daughter cells. The rate and timing of reproduction depend on the conditions like temperature and availability of nutrients. When there is a favorable condition, E.coli or Escherichia coli produces about 2 millions of bacteria in every 7 hours.
Role of bacteria in human health and diseases
Bacteria are both beneficial and detrimental to humans. The most common example of beneficial bacteria are:
- Conversion of milk into curd – Lactobacillales or lactic acid bacteria.
- Used in fermentation food products – Streptococcus and Bacillus.
- Useful in preparation of bread, cakes and other bakery food products.
- The presence of microflora in human guts. A human digestive system is lined by a million of bacteria which help in digestion.
- For the production of antibiotics, used in the treatment and prevention of bacterial infections.
Some bacteria are fatal even though they are very less in their numbers. They can make us sick and cause many deadly diseases like pneumonia, tuberculosis, diphtheria, Syphilis, tooth decay, etc.
There are several sterilization methods used for the eradication of these harmful and disease-causing bacteria. These methods include- application of heat, disinfectants, UV radiations, pasteurization, boiling, etc.
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