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These tiny living creatures are often associated with major diseases like AIDs, meningitis, pneumonia, other infections, or with the reason behind food being spoiled. Truth be told, majority of the microorganisms are the reason behind the balance maintained between the living organisms and chemicals in the environment.
Following are some of the good work done by none other than these microscopic warriors of our life:
Marine and freshwater microbes form the basis of food chain in rivers, lakes, seas and oceans
Soil microbes are responsible for the recycling of chemical elements between soil, water, life, and air for example, by aiding in waste degradation, by incorporating nitrogen gas from the air into organic compounds, etc.
Some organisms are known to play an important role in the process of photosynthesis (a food and oxygen generating crucial life supporting phenomenon).
Intestines of humans and many other animals are a home for a variety of microbes making digestion easier and are responsible for the synthesis of some vitamins required by their body, example, synthesis of some B vitamins for metabolism and vitamin K for blood clotting.
Commercial applications:
Apart from playing crucial roles in various life supporting phenomenon microbes have various commercial applications.
For synthesis of chemical products such as vitamins, organic acids, enzymes, alcohols, and many drugs. Example: production of acetone and butanol, vitamin B2 and B12 (riboflavin and cobalamin).
Vinegar, sauerkraut, pickles, soy sauce, cheese, yogurt, bread, and alcoholic beverages are some of the microbe produced food industry products.
Enzymes from microbes can be manipulated to cause the microbes to produce substances typically not synthesized by them, including cellulose, digestive aids, drain cleaner and insulin (therapeutic product).
Nomenclature:
Nomenclature:
Carolus Linnaeus (1735) established the current system of nomenclature. Latin being the language traditionally used by scholars became the basis of scientific names.
Example: Staphylococcus aureus (a bacterium commonly found on human skin). Both names are either underlined or italicized. Staphylo – describes clustered arrangement of the cells, coccus – indicates sphere shaped, aureus – Latin for golden, the bacterium’s colony colour. After being mentioned once the scientific name can be abbreviated with the initial of the genus followed by the specific epithet (like S. aureus).
More examples: Escherichia coli, Salmonella enterica, Saccharomyces cerevisiae (yeast).
Classification of microorganisms:
Classification of microorganisms:
Microbial taxonomists have always faced trouble while classifying microorganisms due to their diversity. Placing them under either plants or animal kingdom was misleading as some microorganism were motile like animals while others had cell walls and were photosynthetic like plants.
The study of the cellular structure of the microorganisms was an important breakthrough in microbial taxonomy as it was discovered that these cellular microbes had two types of “floor plans”. According to the "floor plan" they were categorised as prokaryotic and eukaryotic.
The table below lists some differences between prokaryotic and eukaryotic cells.
Five Kingdom Classification by R.H. Whittaker:
The observation made above lead to the development of a five kingdom classification scheme by R.H. Whittaker (1969) dividing the organisms into kingdom Monera, Protista, Fungi, Plantae and Animalia with microorganisms being placed in the first three kingdoms (except viruses and other acellular infectious agents, they had their own classification system). All the prokaryotic cells in this classification were placed under Monera and the unicellular eukaryotic organisms were placed in kingdom Protista.
Failure: Although, the five kingdom classification was an important stage in microbial taxonomy it was no longer accepted by microbiologist due to discrepancy caused by classifying all prokaryotes under Monera because not all "prokaryotes" are the same as some differences were noticed in their cell wall composition.
Solution: Six kingdom classification
Six KIngdom Classification by Carl Woese:
Based on cellular organisation of organism a new system of classification was devised by Carl Woese in 1978 grouping all organisms in 3 domains –
1. Bacteria (cell walls contain a protein–carbohydrate complex called peptidoglycan)
2. Archaea (cell walls, if present, lack peptidoglycan)
3. Eukarya, which includes the following:
Protists (slime molds, protozoa, and algae)
Fungi (unicellular yeasts, multicellular molds, and mushrooms)
Plants (mosses, ferns, conifers, and flowering plants)
Animals (sponges, worms, insects, and vertebrates)
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DID YOU KNOW?
Earliest attempts of Classification:
The first attempt to classify organisms was made by Aristotle which divided all the living organisms into Plants and Animals. 'Plants' were further branched to herbs, shrubs and tree based on their morphological characteristics and 'Animals' were further classified on the basis of absence and presence of red blood cells as Anaima and Enaima respectively.
Two Kingdom classification: Linnaeus was the next to classify the organisms into two main kingdoms - Plantae and Animalia. This system of classification did not distinguish between unicellular or multicellular organisms, nor between eukaryotes and prokaryotes neither between photosynthetic and non-photosynthetic organisms which lead to the next two endeavours of classification.
Three Kingdom classification: Protista was suggested as an addition to Linnaeus's 2 kingdom classification by Haeckel to include all the unicellular organisms.
Four Kingdom classification: Monera was proposed as the fourth kingdom by Copeland allowing the classification of all prokaryotes under this kingdom.
References:
<a href='https://www.freepik.com/vectors/background'>Background vector created by freepik - www.freepik.com</a> (Banner used in the top of the page)
Willey, J. M., Sherwood, L., & Woolverton, C. J. (2014). Prescott’s microbiology (Ninth edition). McGraw-Hill.
Gerard J. Tortora, Berdell R. Funke, Christine L. Case (2013), Microbiology: An Introduction (Eleventh edition), Pearson.
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