AUTOTROPHIC BACTERIA: CHARACTERISTICS, DIFFERENCES WITH HETEROTROPHS AND EXAMPLE - BIOLOGY - 2025

The autotrophic bacteria are microorganisms having a metabolic apparatus rather complex. These bacteria are capable of assimilating inorganic matter, to transform it into organic matter, which they then use to make the biomolecules necessary for their development.

Therefore, these types of microorganisms are independent, behaving like free-living organisms. They do not need to invade other organisms, or decompose dead organic matter, to get the nutrients they need to survive.

Red and green autotrophic bacteria. Source: publicdomainpictures.net

Autotrophic bacteria play a fundamental role in the ecosystem, since they provide the organic matter necessary for the development of other living beings. That is, they fulfill vital functions for the maintenance of ecological balance.

These organisms are thought to be the first life form on the planet; And in many ecosystems, they start the food chain.

Autotrophic bacteria are found in various ecological niches. For example, muddy marine snow, fresh and salty waters, hot springs, soils, among others, producing organic matter.

Characteristics of autotrophic bacteria

Depending on the metabolic system that autotrophic bacteria use to take inorganic compounds and transform them into organic compounds, they are classified as photoautotrophs or chemoautotrophs.

Photoautotrophs

Photoautotrophic organisms include algae, plants, and some bacteria. They are characterized by using sunlight as a source of energy to carry out the process of transformation of inorganic to organic matter.

In the case of photoautotrophic bacteria, these are in turn divided into oxygenic and anoxygenic photoautotrophs.

Oxygenic photoautotrophic bacteria

In this type of bacteria, the photosynthesis process occurs, which consists of capturing solar energy through a green pigment called bacteriochlorophyll, and converting it into chemical energy.

Energy is used to take carbon dioxide from the environment and together with water and mineral salts to produce glucose and oxygen. Glucose is used for internal metabolic processes and oxygen is released to the outside.

Anoxygenic Photoautotrophic Bacteria

They are characterized by being anaerobic bacteria, since they do not use oxygen in the respiration process, without it damaging them. They also use sunlight as a source of energy. Some oxidize Fe ² in the absence of oxygen.

Chemoautotrophs

Chemoautotrophic bacteria use chemical energy for their metabolic processes. This is obtained from the oxidation of inorganic compounds, in addition to using CO2 as a carbon source.

Reduced inorganic elements taken from the environment include hydrogen sulfide, elemental sulfur, ferrous iron, molecular hydrogen, and ammonia.

Their existence guarantees the life of other living beings, since the inorganic compounds they take from the environment are toxic to other microorganisms. Furthermore, the compounds released by autotrophic bacteria can be assimilated by some heterotrophic bacteria.

Chemoautotrophic bacteria are very numerous. They generally live in hostile ecosystems, that is, they are extremophiles.

There are also other organisms that behave like autotrophs but belong to other domains. For example, Archaea domain (methanogens and thermoacidophiles). However, since they are not normal bacteria, they will not be considered in this article.

Autotrophic bacteria are classified into halophiles, sulfur oxidizers and reducers, nitrifiers, iron bacteria, and anammox bacteria.

Halophiles

They are bacteria that can withstand high concentrations of salt. These bacteria are usually strict or extreme halophiles. They live in marine environments, such as the Dead Sea.

Sulfur oxidizers

They are also known as sulfoxidant bacteria. These microorganisms take inorganic sulfur from the environment to oxidize it and make their own metabolic products.

That is, they capture hydrogen sulfide (odoriferous gas) generated by the decomposition of organic compounds that contain sulfate, carried out by anaerobic heterotrophic bacteria.

Sulfoxidant bacteria are aerobic chemoautotrophs and convert hydrogen sulfide to elemental sulfur.

They withstand high temperatures, live in extreme ecological niches such as active volcanoes, hot springs or oceanic hydrothermal vents, and in pyrite (iron sulfide mineral) deposits.

Iron bacteria

They can be found in iron-rich soils, rivers, and groundwater. These types of bacteria take iron ions and sometimes manganese in their reduced state and oxidize them, forming iron or manganese oxide.

Iron oxide gives the substrate in which these bacteria live a characteristic reddish-orange color.

Nitrifiers

They are bacteria that are responsible for oxidizing reduced inorganic nitrogen compounds, such as ammonium or ammonia, to convert them into nitrate.

They can be found on the ground, in fresh water, and in salt water. They develop fully where there is a high rate of protein breakdown, with the consequent production of ammonia.

Anammox bacteria

They are bacteria that anaerobically oxidize the ammonium ion and nitrite and form nitrogen gas.

Differences between autotrophic and heterotrophic bacteria

Lifestyle

All types of autotrophic bacteria (photoautotrophs and chemoautotrophs) are free-living, a characteristic they share with photoheterotrophs, while chemoheterotrophs need to obtain their nutrients by parasitizing organisms of another type.

On the other hand, chemoautotrophic bacteria differ from chemoheterotrophs by the habitat where they develop. Chemoautotrophic bacteria often live under extreme environmental conditions, where they oxidize inorganic elements that are toxic to other microorganisms.

In contrast, chemoheterotrophic bacteria usually live inside higher organisms.

Nutrition

Autotrophic bacteria use inorganic matter to synthesize organic compounds. They only need water, inorganic salts and carbon dioxide as a carbon source to live.

While heterotrophic bacteria need for their growth and development a source of carbon from complex organic compounds already made, such as glucose.

Microscopic study

Counting of autotrophic bacteria from some ecosystems can be performed using the epifluorescence-based microscopy method.

This technique uses fluorochrome such as primulin and excitation filters for blue and ultraviolet light. Autotrophic bacteria differ from heterotrophs in that they are colored bright white-blue, without masking the auto-fluorescence of the bacteriochlorophyll, whereas heterotrophs do not stain.

Disease producers

Autotrophic bacteria are saprophytes and do not cause disease in humans, because they do not need to parasitize higher organisms to live.

In contrast, the bacteria that cause infectious diseases in humans, animals and plants belong to the group of heterotrophic bacteria, specifically chemoheterotrophs.

Examples of autotrophic bacteria species

Oxygenic photoautotrophs

In this classification are cyanobacteria. These are the only prokaryotic cells that perform oxygenic photosynthesis.

They are aquatic bacteria, the most common are the genera Prochlorococcus and Synechococcus. Both are part of the marine picoplankton.

The genera Chroococcidiopsis, Oscillatoria, Nostoc, and Hapalosiphon are also known.

Anoxygenic Photoautotrophs

In this classification are:

- The non-sulfurous purple or red bacteria Rhodospirillum rubrum, Rhodobacter sphaeroides, Rhodomicrobium vannielii. However, they can also develop photoheterotrophically.

- Purple or sulfurous red: Chromatium winesum, Thiospirillum jenense, Thiopedia rosea.

- Non-sulfur greens: Chloroflexus and Chloronema.

- Sulfurous greens: Chlorobium limicola, Prosthecochloris aestuarii, Pelodictyon clathratiforme.

- Heliobacterium modesticaldum.

Chemoautotrophs

Colorless sulfur bacteria

Examples: Thiobacillus thiooxidans, Hydrogenovibrio crunogenus.

Nitrogen bacteria

Examples: bacteria of the genera Nitrosomonas, Nitrosococcus, Nitrobacter and Nitrococcus.

Iron bacteria

Examples: Thiobacillus ferrooxidans, Actidithiobacillus ferrooxidans and Leptospirilum ferroxidans.

Hydrogen bacteria

They use molecular hydrogen to carry out their vital processes. Example Hydrogenbacteria.

Anammox bacteria

Examples of freshwater strains: Brocadia, Kuenenia, Jettenia, Anammoxoglobus.

Example of a saltwater strain: Scalindua.

References

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2. "Methanogenesis." Wikipedia, The Free Encyclopedia. 28 Nov 2018, 19:53 UTC. 5 May 2019, 21:11, Available at: es.wikipedia.org.
3. Anammox. Wikipedia, The Free Encyclopedia. 24 Dec 2016, 12:22 UTC. 5 May 2019, 21:13, es.wikipedia.org
4. Gastón J. Elimination of sulphates in an anaerobic-aerobic moving bed reactor. Thesis to qualify for the degree of Master in Environmental Engineering. 2088, Institute of Engineering UNAM. Available at: ptolomeo.unam
5. Nitrifying bacteria. Wikipedia, The Free Encyclopedia. 16 Nov 2018, 15:13 UTC. 5 May 2019, 22:21
6. Corrales L, Antolinez D, Bohórquez J, Corredor A. Anaerobic bacteria: processes that carry out and contribute to the sustainability of life on the planet. NOT GOING. 2015; 13 (23): 55-81. Available at: scielo.org.