Chemoautotroph: Definition, Function, And Examples

Chemoautotroph Definition

A chemoautotroph is an organism that obtains energy through chemosynthesis rather than photosynthesis. They create their own energy and biological materials from inorganic chemicals.

Chemoautotrophs are typically bacteria or protozoa that oxidize inorganic compounds as a source of energy. They use carbon dioxide as their source of carbon, which is the most oxidized form of carbon.

Function of Chemoautotroph

Basis of Ecosystems Without Sunlight

Chemoautotrophs are organisms that can produce their own food using inorganic compounds and energy from chemical reactions instead of sunlight. They form the basis of ecosystems where photosynthesizers cannot survive, such as deep-sea hydrothermal vents and caves.

Without chemoautotrophs, life would only be able to exist where energy could be derived from sunlight.

However, an ecosystem could survive without sunlight as long as it has an alternative energy source. For example, sea creatures living in the very deep ocean rely on volcanoes for energy instead of sunlight. Similarly, ecosystems at the poles of the earth can survive without sunlight during winter months.

Sunlight also provides indirect benefits to life on Earth. It provides heat that is necessary for many organisms to survive. Without sunlight, Earth would be much colder, and parts of Pluto are as cold as -240°C (-400°F).

Nitrogen Fixation

Nitrogen fixation is the process of converting molecular nitrogen (N2) into ammonia (NH3) or related nitrogenous compounds, making it available for absorption by plants.

Nitrogen is a critical limiting element for plant growth and production, as it is a major component of chlorophyll, the most important pigment needed for photosynthesis, as well as amino acids.

Nitrogen fixation can occur through physicochemical and biological processes. Physicochemical processes include lightning strikes and industrial processes.

Biological nitrogen fixation (BNF) occurs naturally in soil or aquatic systems through symbiotic or free-living bacteria that convert N2 into ammonia or other nitrogenous compounds. Symbiotic bacteria live in association with plants such as legumes, while free-living bacteria are found in soil and water.

Nitrogen fixation plays an essential role in maintaining soil fertility and agricultural productivity. It reduces the need for synthetic fertilizers that can have negative environmental impacts such as the eutrophication of water bodies.

The study of biological nitrogen fixation has led to the development of new technologies such as bio fertilizers that can enhance crop yields while reducing environmental impacts.

Possible Origin of Life

The origin of life on Earth is still a mystery, and various hypotheses have been proposed to explain it. One hypothesis suggests that life arose spontaneously from nonliving matter in short periods of time. However, this idea is not supported by scientific evidence.

The earliest evidence of life on Earth comes from fossils discovered in Western Australia that date back to about 3.5 billion years ago. These fossils are of structures known as stromatolites, which are formed by the growth of layer upon layer of single-celled microbes, such as cyanobacteria.

Scientists have proposed several theories about the origin of life. One theory suggests that life may have originated near hydrothermal vents on the ocean floor.

Another theory proposes that life may have been brought to Earth by comets or meteorites. Yet another theory suggests that RNA molecules may have played a role in the origin of life.

Despite these theories, the origin of life remains unverified and is still an active area of research. To better understand what geochemical conditions nurtured the first life forms and find out if we are alone in the galaxy, scientists will need to continue studying this fascinating topic.

Examples of Chemoautotrophs


Nitrosomonas is a genus of Gram-negative bacteria that belongs to the Betaproteobacteria class. It is one of the five genera of ammonia-oxidizing bacteria and uses ammonia as an energy source and carbon dioxide as a carbon source in the presence of oxygen.

Nitrosomonas are important in the nitrogen cycle as they convert soil ammonia to nitrates, which are compounds usable by plants.

Nitrosomonas are rod-shaped chemolithoautotrophs with aerobic metabolism. They burn ammonia with oxygen, using long, thin membranes inside their cells to produce energy by using electrons from ammonia’s nitrogen atom.

Nitrosomonas europaea has two distinct loci for the expression of cytochrome c oxidases, which terminate the aerobic respiratory network. Both clusters contain genes encoding the major catalytic subunit of the oxidase and a smaller subunit where electrons from cytochrome c enter the complex.

Iron Bacteria

Iron bacteria are chemotrophic bacteria that derive energy by oxidizing dissolved iron. They occur naturally in soil, shallow groundwater, and surface waters.

Iron bacteria combine iron (or manganese) and oxygen to form deposits of “rust,” bacterial cells, and a slimy material that sticks the bacteria to well pipes, pumps, and plumbing fixtures.

The colored deposits of these microorganisms are due to the products of ferric (brown) and/or manganese (pink) salts (usually hydroxides).

Iron bacteria can grow and proliferate in waters containing iron concentrations as low as 0.1 mg/L. However, at least 0.3 ppm of dissolved oxygen is needed to carry out the oxidation.

When iron and manganese bacteria oxidize, they produce aggressive ferric chlorides that can eat away at metal pipes and plumbing fixtures, weakening surfaces and pulling flakes of metal into water.

To treat iron bacteria in well water, it is recommended to use a combination of physical removal methods such as filtration or sedimentation followed by chemical treatment with chlorine or hydrogen peroxide. Shock chlorination may also be used periodically to kill off any remaining bacteria.


Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They belong to the domain Archaea and are classified as archaea, a distinct domain of bacteria.

Methanogens help break down organic material in low-oxygen environments and can be found in wetlands, deep oceans, and even the digestive tracts of humans and other animals. Methanogens utilize hydrogen to reduce carbon dioxide, acetate, and a variety of methyl compounds into methane.

Methanogens were earlier believed to inhabit only extreme environments but are now reported to be found in various environments including the human gut. The presence of methanogens in the human gut has been linked with several health conditions such as constipation, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), obesity, and colorectal cancer.

However, some studies suggest that methanogens may also have beneficial effects on human health by reducing inflammation and improving glucose metabolism.

Researchers at MIT have studied the timing of methanogen evolution using molecular clock analysis. They found that early forms of life very likely had metabolisms that transformed the primordial Earth by initiating the carbon cycle and producing most of the planet’s oxygen through photosynthesis.