Microbes are single-cellular organism which are so tiny which can be visible only through microscope. Without them we cannot survive.
Microbes are diverse-protozoa, bacteria, fungi and microscopic plants viruses, viroids and also prions that are proteinacious infectious agents. They are found everywhere on earth ranging from soil, air, water and some inhabitable places.
- Bacteria and fungi can be grown on nutritive media to form colonies, which can be seen by naked eyes and very useful in study of microorganisms.
- Microbes cause many diseases in human beings, plants and animals. Several microorganisms are useful to humans in diverse ways.
A typical bacterium has a rigid cell wall and a thin, rubbery cell membrane surrounding the fluid, or cytoplasm, inside the cell. A bacterium contains all of the genetic information needed to make copies of itself—its DNA—in a structure called a chromosome. In addition, it may have extra loose bits of DNA called plasmids floating in the cytoplasm. Bacteria also have ribosomes, tools necessary for copying DNA so bacteria can reproduce. Some have threadlike structures called flagella that they use to move.
A virus may or may not have an outermost spiky layer called the envelope. All viruses have a protein coat and a core of genetic material, either DNA or RNA. And that’s it. Period.
Which brings us to the main difference between viruses and bacteria—the way they reproduce.
Microbes in household products
- Microorganisms like Lactobacillus and other commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. A small amount of curd added to fresh milk as inoculum or starter contain millions of LAB which multiply at suitable temperature and convert milk into curd. It also improves its nutritional quality by increasing vitamin B12. In our stomach too, the LAB play very beneficial role in checking disease causing
- The dough is used for making foods such as dosa and idli is fermented by the puffed-up appearance of dough is due to the production of CO2 gas. The dough used for making bread is fermented using baker’s yeast (Saccharomyces cervisiae). Microbes are also used to ferment fish, Soyabeans and bamboo shoots to make foods.
- The large holes in ‘Swiss cheese’ are due to production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii. The ‘Roquefort cheese’ are ripened by growing a Penicillium roqueforti a saprotrophic fungus, which gives them a particular flavour.
Microbes in industrial production
A number of products like beverages and antibiotics involve uses of microbes. Production on large scale requires growing microbes in very large vessels called fermentors.
- Fermented Beverages– yeast (Saccharomyces cerevisiae) is used for production of beverages like wine, bear, whisky and rum. Wine and bear are produced without distillation(purification) whereas whisky, brandy and rum are produced by distillation of the fermented.
- Antibiotics– they are chemical substances produced by some microbes and can kill or retard the growth of disease causing bacteria. Penicillin was first antibiotic to be discovered. Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough (kali khansi ), diphtheria (gal ghotu) and leprosy (kusht rog).
- Chemical, Enzymes and other Bioactive Molecules are commercially produced by microbes. Apergillus niger (fungus) produce citric acid, Acetobacter aceti ( bacteria) acetic acid and Lactobacillus (bacterium) lactic acid etc. bioactive molecules cyclosporine A, that is used as an immunosuppressive agent in organ-transplant patients is produced by fungus Trichoderma polysporium.
Microbes in sewage Treatment Municipal waste water (sewage) contains large amount of organic matter and microbes which are pathogenic and cannot be discharged into natural water bodies like rivers and streams.
Sewage is treated in sewage treatment plant to make it less polluting by using heterotrophic microbes naturally present in sewage. Sewage treatment is done in two stages- Primary and Secondary treatment.
- In primary treatment, floating debris is removed by sequential Grit (soil and small pebbles) are removed by sedimentation.
- Secondary treatment or biological treatment involves passing of primary effluents in large aeration tank to help the growth of aerobic microbes into flocs(masses of bacteria associated with fungal filaments to form mesh like
structures). These microbes increase the consumption of organic wastes and decrease the BOD (biological oxygen demand) of the effluents.
- BOD is the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria. BOD is a measure of the organic matter present in the water. The greater the BOD of waste water, more is its polluting potential.
- Sludge is passed into large tanks called anaerobic sludge digesters in which anaerobic bacteria digest the bacteria and fungi in the sludge and produce mixture of gas called biogas, which is a mixture of methane, hydrogen sulphide and carbon dioxide.
- The effluents from the secondary treatment plant are released into water bodies.
Microbes in Production of Biogas
Biogas Plant – the excreta of cattle (gobar) is rich in methanogens bacteria and is used for generation of biogas also called as gobar gas.
- Biogas plant consists of a concrete tank in which bio-wastes are collected and slurry of dung is fed.
- A floating cover is placed over digester that moves upward when gas is The gas produced is removed and supplied through an outlet pipe for consumption.
- The spent slurry is removed through another outlet and used as fertilisers. Biogas plant is more often build in rural areas as large amount of cattle dug is available easily.
Microbes as Biocontrol agent
Biocontrol means use of biochemical method for controlling plant disease and pests. The chemical used as pesticides and insecticides are harmful to human beings and animals. Biological control of pests and disease is a method of controlling pest on natural prediction rather than chemicals. The organic farmer creates a system where the pests are not eradicated but kept at manageable level by complex system of check and balance within the living and vibrant ecosystem. For example, the Ladybird and Dragonflies are used to get rid of aphids and mosquitoes respectively. On brassicas and fruit tree, to control butterfly caterpillars bacteria Bacillus thuringiensis is used.
Biological control developed for used in the treatment of plant disease is the fungus Trichoderma are free-living fungi that are very common in the root systems that control several plant pathogens.
Microbes as Bio fertilisers
Bio fertilisers are organisms that enrich the nutrient quality of the soil. The main sources includes bacteria, fungi and cyanobacteria.
- The root nodule formed by Rhizobium bacteria on root of leguminous plants increase the nitrogen level of soil, necessary for various metabolic Azotobacter and Azospirillum are free living bacteria that live in soil and fix atmospheric nitrogen into organic forms.
- Symbiotic association of fungi with angiosperm plants (mycorrhiza) also increase the fertility of soil. Glomu form mycorrhiza that absorbs phosphorus from the soil and passes it to the plant. These microbes also provide benefits like resistance to root-borne pathogens, tolerance to salinity and drought.
- Cyanobacteria (Nostoc, Anabaena), an autotrophic microbes found in aquatic and terrestrial environment fix atmospheric In paddy field this acts as important bio-fertiliser. Blue green algae also add organic matter to the soil and increase its fertility.