Question

An example of chemoautotrophic bacteria is
(А) Lactobacillus
(B) Nitrosomonas
(C) Escherichia coli
(D) Rhizobium

Answer 1

Hint: Nutrition in bacteria is of two types i.e. autotrophic and heterotrophic. Bacteria having autotrophic mode of nutrition may be photoautotrophs and chemoautotrophs, carrying out photosynthesis and chemosynthesis, respectively.

Complete answer:
Chemosynthetic autotrophic bacteria : Bacteria belonging to this category obtain energy for the synthesis of food by oxidising certain inorganic substances like ammonia, nitrates, nitrites, ferrous ions etc. Thus, they do not utilise light as an energy source. The chemical energy thus obtained is trapped in ATP molecules. This energy is then used in carbon assimilation with the help of hydrogen from some source other than water, e.g., hydrogen bacteria, nitrifying bacteria, sulphur bacteria, etc. They play a great role in recycling nutrients like nitrogen, phosphorus, iron, sulphur.
Now let us match this with given options:-
Lactobacillus :- these bacteria perform heterotrophic mode of nutrition. They convert milk into curd as they convert lactic acid into lactose.
Nitrosomonas :- Nitrosomonas is a genus of the bacteria that fix nitrogen. Nitrogen fixation is an extremely important principle in agriculture where many crops are unable to bind themselves to nitrogen. To guarantee that the soil contains sufficient organic nitrogen so that it can synthesize its food by using chemicals so called as chemoautotrophs
Escherichia coli :- it is a heterotrophic organism that depends on others for food. They obtain their food from the host organism . They obtain food by following the biosynthetic organic pathway.
Rhizobium :- it lives inside the root nodules of leguminous plants. This has the saprophytic mode of nutrition . They obtain their food by using the dead and decaying organism and feeding on them.

Our correct option is B) Nitrosomonas.

Note: Some common chemoautotrophic bacteria are :-
(a) Hydrogen bacteria. Hydrogen monas.
(b) Nitrifying bacteria. Nitrosomonas, Nitro coccus, Nitrobacter and Microcystis
(c) Sulphur bacteria. Thiobacillus thioxidans, Beggiatoa
(d) Iron bacteria. Ferro bacillus, Leptothrix