(a) Heterotrophic Bacteria
Heterotrophic bacteria depend on organic substances for their nutrition. Many of them are extremely useful in agriculture, industry and daily life. Two important economic uses are:
- 1. Decomposition and soil fertility: Many heterotrophic bacteria act as natural decomposers of dead plants, animals and other organic wastes. During decomposition, they convert complex organic matter into simpler substances and help in the formation of humus, thereby improving soil fertility and structure.
- 2. Production of curd and other fermented products: Species of Lactobacillus and related bacteria convert lactose (milk sugar) into lactic acid, causing milk to coagulate and form curd. Similar heterotrophic bacteria are used in the preparation of cheese, yogurt and other fermented foods.
(You may also remember other uses such as production of antibiotics and nitrogen fixation by some soil bacteria, though only two are required in the question.)
(b) Archaebacteria
Archaebacteria are ancient, primitive prokaryotes that often live in extreme environments (high temperature, high salt, absence of oxygen). They also have important economic uses. Two of them are:
- 1. Biogas (methane) production: Methanogenic archaebacteria (methanogens) live in the anaerobic conditions of the rumen of cattle and in cow-dung pits. They produce methane (\(\text{CH}_4\)) during decomposition of organic matter, which is used as biogas (gobar gas) for cooking and lighting.
- 2. Sewage treatment / waste management: Methanogens are used in anaerobic sludge digesters of sewage treatment plants, where they help in breaking down organic matter and generate biogas as a useful by-product.
Short Exam-style Answer
(a) Heterotrophic bacteria: (i) They act as decomposers, break down organic wastes and help in the formation of humus, thus increasing soil fertility. (ii) They are used in the production of curd from milk and in other fermented food products. (b) Archaebacteria: (i) Methanogenic archaebacteria present in the rumen of cattle and in biogas plants produce methane (biogas) from dung and other organic matter. (ii) They are employed in anaerobic digesters of sewage treatment plants to degrade organic wastes and generate useful biogas.