Microbes are diverse Protozoa, bacteria, fungi and microscopic animal and plant virus, viroid's are also prions that are proteinaceous infectious agents. Microbes like bacteria and many fungi can be grown on nutritive media to form colonies that can be seen with the naked eyes, such cultures are useful in studies on microorganisms. It is also true that microbes also cause a large number of diseases in human beings, they also cause diseases in animals and plants but this does not mean that microbes are harmful, microbes are useful to man in various ways, some of the most important contribution of microbes to humans are discussed as follows:

Microbes in household products 

Lactobacillus and other microorganisms known as lactic acid bacteria (LAB) thrive in milk and generate curd. The LAB synthesises acids that coagulate and partly breakdown milk proteins. It also boosts the nutritional quality by adding more vitamin B12.
In our stomach, the LAB also plays an important function, it prevents the growth of disease-causing microorganisms. Bacteria ferment the dough, which is used to make dishes like dosa and idli. The generation of CO2 gas causes the puffed-up look of dough.
Baker's yeast is used to ferment the dough needed to make bread (Saccharomyces cerevisiae).
Toddy’ a traditional drink of some parts of southern India is made by fermenting sap from palms. Cheese is one of the first foods to include microorganisms.
 The big holes in 'Swiss cheese' are caused by a bacteria called Propionibacterium sharmanii producing a huge amount of CO2. The 'Roquefort cheese' is made by cultivating an unique fungus on it to give it a distinct flavor.

Microbes in Industrial Production 

A large number of microbes are used to synthesise various products that are important to humans being, these includes beverages, antibiotics that are produced on industrial scale and requires microbes in very large quantity, for this very large vessels are used that are called fermenters
Let’s have a look at all the industrial products in a bit detail: 
Beverages: Saccharomyces cerevisiae, sometimes known as brewer's yeast, is used for fermenting malted grains and fruit juices to generate drinks such as wine, beer, whiskey, and rum. Wine and beer are not distilled, but whiskey, brandy, and rum are made by distilling the fermented broth.
Antibiotics: They are molecules that are produced by bacteria that have the ability to kill or slow the development of other microorganisms. The first discovered antibiotic was Penicillin. The discovery of penicillin was by chance and was made by Alexander Fleming when he was working on Staphylococcus. However, its full potential as an effective antibiotic was established much later by Ernest Chain and Howard Florey. This antibiotic was extensively used to treat American soldiers wounded in World War II. Fleming, Chain and Florey were awarded the Nobel Prize in 1945, for this discovery.
 Antibiotics have significantly enhanced our ability to cure lethal infections such as plague, whooping cough, diphtheria, and leprosy.

Chemicals, Enzymes and other Bioactive molecules: 

Some of the chemicals produced by microbes are: 
(i) Saccharomyces cerevisiae – Ethanol 
(ii) Acetobacter aceti (bacterium) – Acetic acid 
(iii) Clostridium butylicum (bacterium) – Butyric acid 
(iv) Saccharomyces cerevisiae – Ethanol 
(v) Aspergillus niger (fungus) – Citric acid 
(vi) Lactobacillus (bacterium) – Lactic acid
 Enzymes and their uses:
 (i) Streptokinase is produced by Streptococcus and is used as to remove clots from the blood vessels of patients who have undergone myocardial infarction leading to heart attack. 
(ii) Pectinase and protease are used in used for clearing juices.
 (iii) Lipase is used in laundry detergents.
 Bioactive molecules:
 (i) Cyclosporin A is produced by Trichoderma polysporum a fungi and is used as during organ                      transplant patients. 
(ii) Statins is produced by Monascus purpureus a yeast and is used as blood cholesterol lowering agents.

Microbes in Sewage Treatment 

Municipal sewage comprises of a high concentration of organic materials and harmful bacteria, such a sewage is very harmful and cannot be dumped into rivers and streams. For this sewage is treated, treatment plants are used to reduce pollution by employing heterotrophic bacteria bacteria found naturally in sewage. Sewage treatment is a 2 step process:
Primary Treatment: Floating debris is removed by successive filtering in first treatment. Sedimentation removes grit (dirt and tiny stones). All solids that settle form the primary sludge, and the supernatant forms the effluent. 
Secondary Treatment: Secondary treatmentis also called as biological treatment; it is a process in which primary effluents go through a huge aeration tank to aid in the development of aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh like structures). These bacteria boost organic waste consumption while decreasing effluent BOD (biological oxygen demand). When the BOD of the sewage gets lowered, the effluent is fed into a settling tank, so that tha bacterial flocs can settle. This is called as activated sludge which is pumped into massive tanks known as anaerobic sludge digesters, where anaerobic bacteria consume the bacteria and fungus in the sludge to generate biogas, which is a combination of methane, hydrogen sulphide, and carbon dioxide. The secondary treatment plant's effluent is discharged into bodies of water.
Biological Oxygen Demand: BOD is the quantity of oxygen consumed if bacteria oxidised all of the organic materials in one litre of water. It determines the quantity of organic stuff in the water. If the BOD of the water is high, then it means that water is more flithy.

Microbes in Biogas Production

 Biogas is a gas mixture created by microbial activity that may be used as a fuel. Certain anaerobic bacteria that live on cellulose material create a considerable quantity of methane, CO2 and H2. These microorganisms are known together as methanogens (Methanobacterium).
 Biogas Plant: Cattle excreta (dung) is used to produce biogas as it is rich in these bacteria.
Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC) worked on the technology of Biogas production.
A biogas plant is made up of a concrete tank that collects bio-wastes and feeds dung slurry. When gas is created, a floating cover is placed over the digester and travels upward. The generated gas is extracted and delivered for consumption through an output pipe. The leftover slurry is collected and utilised as fertiliser through another exit. The plants are built in rural locations since significant amounts of dung is conveniently accessible.

As Biocontrol Agents 

Biocontrol refers to the employment of biochemical methods to control plant disease and pests.
Biological pest and disease control is a form of pest control that relies on natural prediction rather than chemicals. In this system pests are not exterminated, but rather managed at a manageable level by a sophisticated system of check and balance inside the living and flourishing ecosystem. e.g. 
(i) Ladybirds and dragonflies, are utilised to control aphids and mosquitoes. 
(ii) Bacillus thuringiensis is used to control butterfly caterpillars on brassicas and fruit trees. 
(iii) Trichoderma are free-living fungus found in root systems that suppress a variety of plant diseases. (iv) The genus Nucleopolyhedrovirus contains the bulk of baculoviruses employed as biological control agents. These viruses are excellent candidates for speciesspecific, narrow spectrum insecticidal applications. These viruses are promising prospects for insecticidal treatments with a species-specific, limited scope.

 Microbes as Biofertilisers 

The organisms that improve the nutritional quality of the soil act as Biofertilisers, e.g. bacteria, fungi, cyanobacteria. Rhizobium generate root nodules on the roots of leguminous plants, thus boosting soil nitrogen concentrations, which are required over many metabolic functions. Azotobacter and Azospirillum are soil-dwelling free-living bacteria that fix atmospheric nitrogen into organic forms.
 is the symbiotic relationship of fungus with angiosperm plants that increases soil fertility. Many members of the genus Glomus form mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant. Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development.
 Cyanobacteria (Nostoc, Anabaena) are autotrophic microorganisms that fix atmospheric nitrogen. This is used on paddy fields.

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