Which pair of microbes includes both microbes that can be used as biofertilisers?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Cyanobacteria and Rhizobium
Biofertilisers are organisms that enrich the nutrient quality of the soil. Their main sources are bacteria, fungi and cyanobacteria. Rhizobium lives in root nodules of legumes and fixes nitrogen; cyanobacteria such as Anabaena and Nostoc fix nitrogen in paddy fields. Microbes used for making acids are a different group.
Option (1) Aspergillus and Lactobacillus — Incorrect. Aspergillus niger is a fungus used to produce citric acid, and Lactobacillus produces lactic acid and turns milk into curd. Neither is used as a biofertiliser.
Option (2) Rhizobium and Acetobacter aceti — Incorrect. Rhizobium is a biofertiliser, but Acetobacter aceti is a bacterium used for commercial production of acetic acid. Only one microbe of the pair fits.
Option (3) Cyanobacteria and Rhizobium — Correct. Both are nitrogen fixers. Rhizobium fixes nitrogen in the root nodules of leguminous plants, and cyanobacteria serve as an important biofertiliser in paddy fields, where they also add organic matter to the soil.
Option (4) Aspergillus and Cyanobacteria — Incorrect. Cyanobacteria are biofertilisers, but Aspergillus is a citric acid producer. Only one microbe of the pair fits.
NCERT Extract:
Microbes as Biofertilisers – “… Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria. You have studied about the nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient.”
Microbes as Biofertilisers – “… In paddy fields, cyanobacteria serve as an important biofertiliser.”
Chemicals, Enzymes and other Bioactive Molecules – “… Examples of acid producers are Aspergillus niger (a fungus) of citric acid, Acetobacter aceti (a bacterium) of acetic acid; Clostridium butylicum (a bacterium) of butyric acid and Lactobacillus (a bacterium) of lactic acid.”