Microbes in Human Welfare

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10.1 Microbes in Household
10.2 Microbes in Industrial
10.3 Microbes in Sewage
10.4 Microbes in Production of
10.5 Microbes as Biocontrol
10.6 Microbes as Biofertilisers

Besides macroscopic plants and animals, microbes are
the major components of biological systems on this earth.
You have studied about the diversity of living organisms
in Class XI. Do you remember which Kingdoms among
the living organisms contain micro-organisms? Which are
the ones that are only microscopic? Microbes are present
everywhere – in soil, water, air, inside our bodies and that of other animals and plants. They are present even at sites
where no other life-form could possibly exist – sites such as deep inside the geysers (thermal vents) where the
temperature may be as high as 1000C, deep in the soil,
under the layers of snow several metres thick, and in highly acidic environments. Microbes are diverse– protozoa,
bacteria, fungi and microscopic plants viruses, viroids and
also prions that are proteinacious infectious agents. Some
of the microbes are shown in Figures 10.1 and 10.2.
Microbes like bacteria and many fungi can be grown
on nutritive media to form colonies (Figure 10.3), that can
be seen with the naked eyes. Such cultures are useful in
studies on micro-organisms.





Figure10.1 Bacteria: (a) Rod-shaped,
magnified 1500X ; (b) Spherical
shaped, magnified1500X; (c) A rodshaped bacterium showing flagella, magnified 50,000X

Figure 10.2

Viruses: (a) A bacteriophage; (b)
Adenovirus which causes respiratory
infections; (c) Rod-shaped Tobacco
Mosaic Virus (TMV). Magnified about

1 80


Figure 10.3 (a) Colonies of bacteria growing in a petri dish; (b) Fungal colony growing in a petri dish


In chapter 8, you have read that microbes cause a large number of diseases in human beings. They also cause diseases in animals and plants. But this should not make you think that all microbes are harmful; several microbes are useful to man in diverse ways. Some of the most important contributions of microbes to human welfare are discussed in this chapter.




You would be surprised to know that we use microbes or products derived from them everyday. A common example is the production of curd from milk. Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins. A small amount of curd added to the fresh milk as inoculum or starter contain millions of LAB, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing vitamin B12. In our stomach too, the LAB play very beneficial role in checking diseasecausing microbes. The dough, which is used for making foods such as dosa and idli is also fermented by bacteria. The puffed-up appearance of dough is due to the production of CO2 gas. Can you tell which metabolic pathway is taking place resulting in the formation of CO2? Where do you think the bacteria for these fermentations came from? Similarly the dough, which is used for making bread, is fermented using baker’s yeast (Saccharomyces cerevisiae). A number of traditional drinks and foods are also made by fermentation by the microbes. ‘Toddy’, a traditional drink of some parts of southern India is made by fermenting sap from palms. Microbes are also used to ferment fish, soyabean and bambooshoots to make foods. Cheese, is one of the oldest food items in which microbes were used. Different varieties of cheese are known by their characteristic texture, flavour and taste, the specificity coming from the microbes used. For example, the large holes in ‘Swiss cheese’ are...
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