Microbes in Human Welfare

CHAPTER EIGHT

MICROBES IN HUMAN WELFARE

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 Eleven. 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 one hundred degrees Celsius, 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 animal and plant viruses, viroids and also prions that are proteinacious infectious agents. Some of the microbes are shown in Figures eight point one and eight point two.

Microbes like bacteria and many fungi can be grown on nutritive media to form colonies (Figure eight point three), that can be seen with the naked eyes. Such cultures are useful in studies on micro-organisms.

In chapter seven, 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.

Eight point one MICROBES IN HOUSEHOLD PRODUCTS

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 grow in milk and convert it to curd. During growth, the lactic acid bacteria 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 lactic acid bacteria, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing vitamin B twelve. In our stomach too, the lactic acid bacteria play very beneficial role in checking disease-causing 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 carbon dioxide gas. Can you tell which metabolic pathway is taking place resulting in the formation of carbon dioxide? Where do you think the bacteria for these fermentations come 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 bamboo-shoots 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 due to production of a large amount of carbon dioxide by a bacterium named Propionibacterium sharmanii. The 'Roquefort cheese' are ripened by growing a specific fungi on them, which gives them a particular flavour.