Chemoautotrophic mode of nutrition is a type of nutrition that is classified under autotrophic means. Now a question has arisen, what is the Autotrophic mode of nutrition? The autotroph is a Greek word that means self-feed. The autotrophic mode of nutrition may be defined as the organisms which are capable of synthesising their food by themselves from organic and inorganic substances. They are the producers in a food chain. The autotrophs can be further divided into two subgroups, i.e. Photoautotrophs, and chemoautotrophs.
Photoautotrophic nutrition is the process by which organisms synthesise their own food by the process of photosynthesis. They are capable of converting radiant energy into chemical energy. While chemoautotrophic nutrition is the process by which organisms synthesise their own food by the process of oxidising inorganic chemical compounds and obtaining energy through this process.
What is Chemoautotrophic Nutrition?
Chemoautotrophic nutrition means the energy derived from chemical reactions that take place. During this mode of nutrition, organisms use inorganic compounds to synthesise several organic compounds with the existence of carbon atoms. Those organisms that possess such a mode of nutrition are known as chemoautotrophs. They are characterised by ⅰ) high specificity with respect to an inorganic energy source, and ⅱ) frequent inability to use organic compounds as energy and carbon sources. But sometimes, their growth is adversely affected by organic compounds.
Chemoautotrophs derive energy from ammonia, nitrate, nitrite, ferrous iron, hydrogen sulphide, and other inorganic compounds for the synthesis of their food. They are non-photosynthetic but autotrophic organisms. Chemoautotrophs are the most abundant and are important geochemical agents. Chemoautotrophs grow in a strictly mineral medium on dark, seafloor where sunlight cannot reach, and sometimes on dead and decaying matter.
Examples of Chemoautotrophic Nutrition
Examples of chemoautotrophic nutrition mostly include prokaryotic organisms like bacteria. Bacteria get energy from oxidising compounds and are hence known as chemoautotrophic bacteria. On the basis of substrate specificity, some examples of chemotrophic bacteria are given below.
Sulphur Bacteria
These bacteria occur in sulphur-containing terrestrial and aquatic environments. They derive energy from the oxidation of reduced sulphur compounds. The sulphur bacterium, Thiobacillus thiooxidans, utilises free sulphur and produces sulphuric acid.
Iron Bacteria
These bacteria form natural colonies in freshwater ponds and springs with high contents of reduced sulphur salts. They oxidise ferrous compounds into ferric forms and the energy released in this process is utilised in the synthesis of organic compounds. The ferric ion is deposited as insoluble ferric hydroxide.
For example, Ferrobacillus, Gallionella, Leptothrix, etc.
Hydrogen Bacteria
These bacteria have the ability to grow with molecular hydrogen. They oxidise molecular hydrogen and in this process, water and energy are obtained. The common hydrogen oxidising bacteria are Acaligens, P. facilis, Nocardia opaca, Paracoccus detrificans, etc.
Nitrifying Bacteria
These are soil-borne obligate autotrophs incapable of growing in the absence of specific inorganic energy sources. They oxidise ammonia to nitrate and help greatly in the economy of nitrogen in nature. The nitrification process is carried out in two steps. Each step is performed by a specific group of bacteria. The first step involves the oxidation of ammonia or ammonium ions to nitrate with the help of Nitrosomonas. The second step of nitrification involves the oxidation of nitrite to nitrate with the help of Nitrobacter.
Mechanism used by Chemoautotrophs
Chemoautotrophs are organisms that synthesise their food with the help of chemical reactions. Such reactions convert the inorganic form to organic forms in order to derive energy. The mechanism used by chemoautotrophs generally refers to chemosynthesis, which means energy produced by oxidation of inorganic substances in the chemical reactions. Originally, the word Chemosynthesis was given by Wilhelm Pfeffer in 1897.
Conclusion
Chemoautotrophic nutrition means the energy derived from the oxidation of inorganic substances during chemical reactions. This mode of nutrition is generally preferred by prokaryotes like bacteria and hence are known as chemoautotrophic bacteria. They use different types of mechanisms, and substrates in order to derive energy by the oxidation of inorganic substances. For example, sulphur bacteria, hydrogen bacteria, iron bacteria, and nitrifying bacteria like Nitrosomonas, Nitrobacter, and cyanobacteria.