Among living organisms, microorganisms are the third domain of classification. This domain includes every unicellular and multicellular microbe like bacteria, protozoa, viruses and so on. Bacteria are inquisitive species for scientist due to many characteristics. They have a long term mutual relationship with humans which are somewhat complex. At times it becomes fatal for other life forms.
Definition and Structure
Bacteria are known for their simple body design. They are single-celled microorganisms with no well-defined nucleus or cell organelles. They are prokaryotic organisms which are present almost everywhere 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 is locomotory organ as well as attaching part. They do not contain any cell organelle as in animals or plants except ribosomes. Ribosomes are the site of synthesis of proteins. Although they possess DNA, it floats within cell and region where DNA is present is called nucleoid. In addition to this DNA, they have an extra circular DNA called plasmid. These plasmids make some strains of bacteria antibiotic resistant.
Bacteria are grouped into five based on their shapes such as rod-shaped bacilli, spherical cocci, comma-shaped vibrios, spiral shaped spirilla and corkscrew spirochaetes. They may either be in clusters or chains or pairs or single. Another criterion for classification is staining, e.g. Gram positive and Gram negative 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 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 produces about 2 million bacteria in every 7 hours.
Bacteria and Human
Bacteria are of two types-useful and harmful. The most common example of beneficial bacteria is microflora in human guts. Human digestive system is lined by a million of bacteria which help in digestion. Other examples are a conversion of milk into curd, baking of bread and cakes, fermentation and antibiotics, etc. Some bacteria are fatal even though they are less in number. They can make us sick and cause many deadly diseases like pneumonia.
Some sterilization methods can be used for eradication of such bacteria. Heat, disinfectants, UV radiations, etc. are some of them. But nowadays, bacteria have become resistant to all these.