Chemosynthesis is the conversion of carbon compounds and other molecules into organic compounds. In this biochemical reaction, methane or an inorganic compound, such as hydrogen sulfide or hydrogen gas, is oxidized to act as the energy source. In contrast, the energy source for photosynthesis (the set of reactions through which carbon dioxide and water are converted into glucose and oxygen) uses energy from sunlight to power the process.
The idea that microorganisms could live on inorganic compounds was proposed by Sergei Nikolaevich Vinogradnsii (Winogradsky) in 1890, based on research conducted on bacteria which appeared to live from nitrogen, iron, or sulfur. The hypothesis was validated in 1977 when the deep sea submersible Alvin observed tube worms and other life surrounding hydrothermal vents at the Galapagos Rift. Harvard student Colleen Cavanaugh proposed and later confirmed the tube worms survived because of their relationship with chemosynthetic bacteria. The official discovery of chemosynthesis is credited to Cavanaugh.
Organisms that obtain energy by oxidation of electron donors are called chemotrophs. If the molecules are organic, the organisms are called chemoorganotrophs. If the molecules are inorganic, the organisms are terms chemolithotrophs. In contrast, organisms that use solar energy are called phototrophs.
Chemoautotrophs and Chemoheterotrophs
Chemoautotrophs obtain their energy from chemical reactions and synthesize organic compounds from carbon dioxide. The energy source for chemosynthesis may be elemental sulfur, hydrogen sulfide, molecular hydrogen, ammonia, manganese, or iron. Examples of chemoautotrophs include bacteria and methanogenic archaea living in deep sea vents. The word "chemosynthesis" was originally coined by Wilhelm Pfeffer in 1897 to describe energy production by oxidation of inorganic molecules by autotrophs (chemolithoautotrophy). Under the modern definition, chemosynthesis also describes energy production via chemoorganoautotrophy.
Chemoheterotrophs cannot fix carbon to form organic compounds. Instead, they can use inorganic energy sources, such as sulfur (chemolithoheterotrophs) or organic energy sources, such as proteins, carbohydrates, and lipids (chemoorganoheterotrophs).
Where Does Chemosynthesis Occur?
Chemosynthesis has been detected in hydrothermal vents, isolated caves, methane clathrates, whale falls, and cold seeps. It has been hypothesized the process may permit life below the surface of Mars and Jupiter's moon Europa. as well as other places in the solar system. Chemosynthesis can occur in the presences of oxygen, but it is not required.
Example of Chemosynthesis
In addition to bacterial and archaea, some larger organisms rely on chemosynthesis. A good example is the giant tube worm which is found in great numbers surrounding deep hydrothermal vents. Each worm houses chemosynthetic bacteria in an organ called a trophosome. The bacteria oxidize sulfur from the worm's environment to produce the nourishment the animal needs. Using hydrogen sulfide as the energy source, the reaction for chemosynthesis is:
12 H2S + 6 CO2 → C6H12O6 + 6 H2O + 12 S
This is much like the reaction to produce carbohydrate via photosynthesis, except photosynthesis releases oxygen gas, while chemosynthesis yields solid sulfur. The yellow sulfur granules are visible in the cytoplasm of bacteria that perform the reaction.
Another example of chemosynthesis was discovered in 2013 when bacteria were found living in basalt below the sediment of the ocean floor. These bacteria were not associated with a hydrothermal vent. It has been suggested the bacteria use hydrogen from the reduction of minerals in seawater bathing the rock. The bacteria could react hydrogen and carbon dioxide to produce methane.
Chemosynthesis in Molecular Nanotechnology
While the term "chemosynthesis" is most often applied to biological systems, it can be used more generally to describe any form of chemical synthesis brought about by random thermal motion of reactants. In contrast, mechanical manipulation of molecules to control their reaction is called "mechanosynthesis". Both chemosynthesis and mechanosynthesis have the potential to construct complex compounds, including new molecules and organic molecules.
Chemosynthetic Bacteria
Chemosynthetic bacteria are organisms that use inorganic molecules as a source of energy and convert them into organic substances. Chemosynthetic bacteria, unlike plants, obtain their energy from the oxidation of inorganic molecules, rather than photosynthesis. Chemosynthetic bacteria use inorganic molecules, such as ammonia, molecular hydrogen, sulfur, hydrogen sulfide and ferrous iron, to produce the organic compounds needed for their subsistence.
Most chemosynthetic bacteria live in environments where sunlight is unable to penetrate and which are considered inhospitable to most known organisms. Chemosynthetic bacteria usually thrive in remote environments, including the Arctic and Antarctic polar regions, where they can be found deep into the ice; they are also found many miles deep in the ocean where sunlight is unable to infiltrate or several meters deep into the Earth’s crust.
Chemosynthetic bacteria are chemoautotrophs because they’re able to use the energy stored in inorganic molecules and convert them in organic compounds. They're primary producers because they produce their own food. An organism that produces organic molecules from organic carbon is classified as a chemoheterotroph. Chemoheterotrophs are at the second level in a food chain.
How Do Living Organisms Obtain Their Energy?
All living organisms obtain their energy in two different ways. The means by which organisms obtain their energy depends on the source from which they derive that energy. Some organisms obtain their energy from the sun by the process of photosynthesis. These organisms are known as phototrophs because they can make their own organic molecules using sunlight as a source of energy. Among the organisms that can use sunlight as a source of energy include plants, algae and some species of bacteria.
The organic molecules produced by phototrophs are used by other organisms known as heterotrophs, which derive their energy from phototrophs, that is to say, they use the energy from the sun, indirectly, by feeding on them, producing the organic compounds for their subsistence. Heterotrophs include animals, humans, fungi, and some species of bacteria, such as those found in the human intestines.
Photosynthesis
Phototroph
Phototroph | Source
Chemosynthesis
The second way in which organisms can obtain their energy is through chemosynthesis. Organisms living in regions where sunlight is not available produce their energy by the process of chemosynthesis. During chemosynthesis, bacteria use the energy derived from the chemical oxidation of inorganic compounds to produce organic molecules and water.
This process occurs in the absence of light. the life forms that utilize this method of obtaining energy are found in places, such as soil, petroleum deposits, ice caps, lava mud, animal gut, hot springs and hydrothermal vents, among many others.
Hot Spring
Hot Spring
Hot Spring | Source
What is the Difference between Photosynthesis and Chemosynthesis?
The survival of many organisms living in the ecosystems of the world depends on the ability of other organisms to convert inorganic compounds into energy that can be used by these and other organisms. Plants, algae, and bacteria have the ability to use sunlight, water, and carbon dioxide (CO2) and convert them into organic compounds necessary for life in a process called photosynthesis. Photosynthesis may take place in marine or terrestrial environments where the producing organisms are able to use sunlight as a source of energy.
Chemosynthesis occurs in environments where sunlight is not able to penetrate, such as in hydrothermal vents at the bottom of the ocean, coastal sediments, volcanoes, water in caves, cold seeps in the ocean floor, terrestrial hot springs, sunken ships, and within the decayed bodies of whales, among many others. Chemosynthetic bacteria use the energy stored within inorganic chemicals to synthesize the organic compounds needed for their metabolic processes.
Hydrothermal Vent
Hydrothermal Vent
Hydrothermal Vent
Chemosynthetic Bacteria in Hydrothermal Vents
Hydrothermal vents are fissures in the deep ocean crust where super-heated lava and magma seep, releasing dissolved chemicals when coming in contact with the deep ocean’s cold water. The dissolved chemicals, including hydrogen sulfide, methane, and reduced sulfate metals, form chimney-like structures known as black smokers. Hydrothermal vents are located very deep into the ocean where sunlight is unable to penetrate; therefore, the organisms that live at hydrothermal vents obtain their energy from the chemicals ejected out from the ocean crust.
Around hydrothermal vents, many miles below the ocean’s surface, there exists a community of organisms that utilize the substances coming out from the cracks as sources of energy to produce organic material. The giant tube worm (Riftia pachyptila) lives in a symbiotic relationship with sulfur-oxidizing bacteria. Since the energy from the Sun cannot be utilized at such depths, the tube worm absorbs hydrogen sulfide from the vent and provides it to the bacteria. The bacteria capture the energy from the sulfur and produces organic compounds for both the tube worm and the bacteria.
Giant Tube Worm
Giant Tube Worm
Giant Tube Worm | Source
What Are Extremophiles?
Extremophiles are organisms that thrive under conditions that are considered detrimental for most organisms. These organisms can live in habitats where no other organisms can, and are capable of tolerating a wide range of hostile environmental conditions. These organisms are termed based on the conditions in which they grow, thus, some are thermophiles, psychrophiles, acidophiles, halophiles, etc. There are extremophiles that are able to grow in more than one habitat and are termed polyextremophiles.
Microbes are extremely adaptable to harsh environment conditions and it is believed that extremophiles could be found in every unimaginable place on Earth. Extremophiles are organisms that can live in very harsh environments. Although most of them are microbes, there are some which do not fall into the classification of archaea and bacteria
It is believed that the first organisms inhabiting the Earth were chemosynthetic bacteria that produced oxygen and later evolved into animal and plant-like organisms. Some organisms that rely on chemosynthesis to derive the energy they need include nitrifying bacteria, sulfur-oxidizing bacteria, sulfur-reducing bacteria, iron-oxidizing bacteria, halobacterium, bacillus, clostridium, and vibrio, among others.
Question:What is the ecological importance of chemosynthetic bacteria?
Answer:
Bacteria play an important role in the environment both in and out of the water. Bacteria help decompose the remains of plants and animals and other waste into nutrients that other living organisms can use.
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Question:How do chemosynthetic bacteria perform sexual reproduction?
Answer:
Many bacteria reproduce through the process of binary fission, a form of asexual reproduction in which bacteria divides into two or more parts. This division may double the quantity of bacteria in minutes. Some bacteria can grow to a quantity that surpasses the number of human beings on earth in just a few hours
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Question:Do chemosynthetic organisms convert energy, stored within inorganic molecules, into chemical energy for primary production?
Answer:
Chemosynthetic organisms-also called chemoautotrophs-use carbon dioxide, oxygen and hydrogen sulfide to produce sugars and amino acids that other living creatures can use to survive. They are the primary producers in their food web. An example of this is the bacteria living inside the tubeworms in a hydrothermal vent
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Question:When there is no hydrothermal vent, how does the bacteria make food?
Answer:
Chemosynthesis can develop in the cracks of the ocean´s crust. The bacteria that are found there can synthesize methane by combining hydrogen and carbon dioxide. It's believed that the chemical reactions that occur on earth could occur on other planets where the conditions are similar to those on earth
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Question:How could the discovery of chemosynthesis change the way in which scientists look for life on other planets?
Answer:
Scientists have discovered that there exist bodies of water and ocean depths in other worlds, such as the moons of Europa and Ganymede; moons of Jupiter but also on Ceres and Enceladus; moon of Saturn, among many other beyond the earth bodies. It´s thought that on the depths of these bodies there could be life forms similar to the ones found on the earth's ocean floor
ENERGY AND FOOD WEBS
All living things require energy in order to survive and carry out their life processes, such as growth, reproduction and for their metabolism. For example, when thinking about our Ocean Tracks species, a large amount of energy is required to migrate the thousands of miles they may travel.
This energy comes from the organism’s ecosystem and in many cases from the food that organism eats. But where did the energy in those food sources come from?
For much of the life on Earth, the primary source of energy is from the sun. Through photosynthesis, plants are able to capture energy from sunlight and use that energy to power reactions that transform carbon dioxide and water into oxygen and sugar molecules. This process removes carbon dioxide from the atmosphere and provides the oxygen that we breathe.
Life is possible, however, even in the absence of sunlight. For example, microbes living in hydrothermal vent communities are able to use inorganic chemical compounds through a process known as chemosynthesis to create energy. These chemosynthetic microbes are the foundation of the food web in hydrothermal vent communities. Photosynthesis and chemosynthesis make it possible for life to exist on Earth!
Organisms that are able to capture energy either from sunlight or chemicals and convert it into a form that other organisms can use are called autotrophs.
Autotrophs are also known as primary producers, and are are a highly important food source for other organisms. On land, primary producers are mostly plants such as grass in trees. In the ocean, 95% of the primary production is done by microscopic phytoplankton. Phytoplankton contribute 50% of the oxygen in our atmosphere. Some phytoplankton are bacteria and others are protists. Two important types of phytoplankton that are diatoms and dinoflagellates.
In coastal regions of the ocean, algae, such as kelps and rockweeds, and plants, such as sea grasses, are important primary producers.
For organisms that cannot make their own food, they must ingest other organisms to fulfill their energy requirements. These organisms are called heterotrophs. Heterotrophs are also called consumers because they must consume other organisms for energy and nutrients.
Consumers obtain their energy in different ways:
There are herbivores that feed on plant material. In the ocean, an example of an herbivore would be a periwinkle grazing on some algae.
There are carnivores that kill and eat other animals. In the ocean, of course one of the greatest carnivores is the great white shark.
There are scavengers and detritivores that feed on dead plants and animals, such as a hagfish feeding on a dead whale in the deep ocean.
Omnivores feed on both plants and animals. The hawksbill sea turtle is an omnivore, feeding on sea urchins, mollusks, crustaceans and algae.
Decomposers are bacteria that chemically break down organic matter.
A food chain is a set of linkages that show who eats who in an ecosystem and the transfer of energy that takes place.
Food chains start with a primary producer. Energy is then transferred to a primary consumer, then secondary, tertiary, and quaternary consumers in sequence.
The primary consumer is an organism that eats a primary producer, which can include a zooplankton or snail in the ocean.
The secondary consumer is an organism that eats a primary consumer, and includes fish species that feed on the zooplankton.
Tertiary consumers feed on secondary consumers, and quaternary consumers feed on tertiary consumers. These groups include higher level predators such as sharks.
In reality most ecosystems are more complicated than a simple chain of feeding interactions. Many species consume more than one type of species, creating a complex web of interactions known as a food web.
In the visual below, you can see an example of a food web in the open ocean ecosystem and also one food chain that is a part of that food web. You may notice, however, that even the picture of the food web is incomplete since only a small number of ocean species are represented.
foodwebchain
Each step of the food web or chain is called a trophic level. Primary producers are always the first trophic level and are represented at the bottom of an ecological pyramid. The diagram below shows an example of an ecological pyramid for the ocean.
trophiclevel
These pyramids can also show how much energy is available at each trophic level of a food web. The average amount of energy transferred from one trophic level to the next is 10%. For example, 10% of the solar energy that is captured by phytoplankton gets passed on to zooplankton (primary consumers). Ten percent of that energy (10% of 10%, which is 1%) gets passed on to the organisms (secondary consumers) that eat the zooplankton.
With more trophic levels that exist between the primary producer and a consumer, the smaller the amount of energy that gets passed on to the consumer. The shape of the pyramid reflects the idea that they amount of energy gets smaller as you move up the food chain. The visual below shows how little energy gets passed along as you get higher in the food chain.
energytransfer
Photosynthesis is the process by which plants use the sun’s energy to make sugar (glucose) for food. Plants absorb energy from sunlight, take in carbon dioxide from the air through their leaves, take up water through their roots, and produce glucose and oxygen. Photosynthesis takes place on land and in shallow water where sunlight can reach seaweeds.
Chemosynthesis is the process by which food (glucose) is made by bacteria using chemicals as the energy source, rather than sunlight. Chemosynthesis occurs around hydrothermal vents and methane seeps in the deep sea where sunlight is absent. During chemosynthesis, bacteria living on the sea floor or within animals use energy stored in the chemical bonds of hydrogen sulfide and methane to make glucose from water and carbon dioxide (dissolved in sea water). Pure sulfur and sulfur compounds are produced as by-products.
In the diagram mussels and tubeworms are using the hydrogen sulfide released from a hydrothermal vent. The chemical equation given here for chemosynthesis is just one of a number of possibilities.
In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydrogen sulfide) or methane as a source of energy, rather than sunlight, as in photosynthesis. Chemoautotrophs, organisms that obtain carbon through chemosynthesis, are phylogenetically diverse, but also groups that include conspicuous or biogeochemically-important taxa include the sulfur-oxidizing gamma and epsilon proteobacteria, the Aquificae, the methanogenic archaea and the neutrophilic iron-oxidizing bacteria.
Many microorganisms in dark regions of the oceans use chemosynthesis to produce biomass from single carbon molecules. Two categories can be distinguished. In the rare sites at which hydrogen molecules (H2) are available, the energy available from the reaction between CO2and H2 (leading to production of methane, CH4) can be large enough to drive the production of biomass. Alternatively, in most oceanic environments, energy for chemosynthesis derives from reactions in which substances such as hydrogen sulfide or ammonia are oxidized. This may occur with or without the presence of oxygen.
Many chemosynthetic microorganisms are consumed by other organisms in the ocean, and symbiotic associations between chemosynthesizers and respiring heterotrophs are quite common. Large populations of animals can be supported by chemosynthetic secondary production at hydrothermal vents, methane clathrates, cold seeps, whale falls, and isolated cave water.
It has been hypothesized that chemosynthesis may support life below the surface of Mars, Jupiter's moon Europa, and other planets.[1]Chemosynthesis may have also been the first type of metabolism that evolved on Earth, leading the way for cellular respiration and photosynthesis to develop later.
Hydrogen sulfide chemosynthesis process[edit]
Giant tube worms use bacteria in their trophosome to fix carbon dioxide (using hydrogen sulfide as an energy source) and produce sugars and amino acids.[2] Some reactions produce sulfur:
- hydrogen sulfide chemosynthesis:[3]
- 12H2S + 6CO2 → C6H12O6 (carbohydrate) + 6H2O + 12S
Instead of releasing oxygen gas while fixing carbon dioxide as in photosynthesis, hydrogen sulfide chemosynthesis produces solid globules of sulfur in the process. In bacteria capable of chemoautotrophy (a form a chemosynthesis), such as purple sulfur bacteria[4], yellow globules of sulfur are present and visible in the cytoplasm.
Discovery[edit]
In 1890, Sergei Winogradsky proposed a novel type of life process called "anorgoxydant". His discovery suggested that some microbes could live solely on inorganic matter and emerged during his physiological research in the 1880s in Strasbourg and Zürich on sulfur, iron, and nitrogen bacteria.
In 1897, Wilhelm Pfeffer coined the term "chemosynthesis" for the energy production by oxidation of inorganic substances, in association with autotrophic carbon dioxide assimilation—what would be named today as chemolithoautotrophy. Later, the term would be expanded to include also chemoorganoautotrophs, which are organisms that use organic energy substrates in order to assimilate carbon dioxide.[5] Thus, chemosynthesis can be seen as a synonym of chemoautotrophy.
The term "chemotrophy", less restrictive, would be introduced in the 1940s by André Lwoff for the production of energy by the oxidation of electron donors, organic or not, associated with auto- or heterotrophy.[6][7]
Hydrothermal vents[edit]
The suggestion of Winogradsky was confirmed nearly 90 years later, when hydrothermal ocean vents were predicted to exist in the 1970s. The hot springs and strange creatures were discovered by Alvin, the world's first deep-sea submersible, in 1977 at the Galapagos Rift. At about the same time, then-graduate student Colleen Cavanaugh proposed chemosynthetic bacteria that oxidize sulfides or elemental sulfur as a mechanism by which tube wormscould survive near hydrothermal vents. Cavanaugh later managed to confirm that this was indeed the method by which the worms could thrive, and is generally credited with the discovery of chemosynthesis.[8]
A 2004 television series hosted by Bill Nye named chemosynthesis as one of the 100 greatest scientific discoveries of all time.[9][10]
Oceanic crust[edit]
In 2013, researchers reported their discovery of bacteria living in the rock of the oceanic crust below the thick layers of sediment, and apart from the hydrothermal vents that form along the edges of the tectonic plates. Preliminary findings are that these bacteria subsist on the hydrogen produced by chemical reduction of olivine by seawater circulating in the small veins that permeate the basalt that comprises oceanic crust. The bacteria synthesize methane by combining hydrogen and carbon dioxide.[1
Chemotrophs are organisms that obtain energy through chemical process called chemosynthesis rather than by photosynthesis. Chemosynthesis is carried out by chemotrophs through the oxidation of electron donors in the environment. Chemotrophs may be chemoautotroph or chemoheterotroph.
Chemoheterotrophs are chemotrophs that are heterotrophic organisms. They are not capable of fixing carbon to form their own organic compounds. They may be further classified as chemolithoheterotrophs or chemoorganoheterotrophs. Chemolithoheterotrophs are those that utilize inorganic energy sources whereas chemoorganoheterotrophs are those using organic energy sources. Chemoorganoheterotrophs may be further grouped based on the kind of organic substrate and compound they use. Decomposers obtain these substrates and compounds from dead organic matter. Herbivores and carnivores derive theirs from living organic matter.
Most chemoheterotrophs obtain energy by ingesting organic molecules like glucose. In contrast, chemoautotrophs are autotrophs that use chemical energy to produce carbohydrates. They utilize inorganic compounds such as hydrogen sulfide, sulfur, ammonium, and ferrous iron as reducing agents, and synthesize organic compounds from carbon dioxide.
Chemosynthesis is the conversion of inorganic carbon-containing compounds into organic matter such as sugars and amino acids. Chemosynthesis uses energy from inorganic chemicals to perform this task.
The inorganic “energy source” is usually a molecule that has electrons to spare, such as hydrogen gas, hydrogen sulfide, ammonia, or ferrous iron. Like photosynthesis and cellular respiration, chemosynthesis uses an electron transport chain to synthesize ATP.
After having its electrons passed through the electron transport chain, the chemical fuel source emerges in a different form. Hydrogen sulfide gas, for example, is converted into solid elemental sulfur plus water.
The term “chemosynthesis” comes from the root words “chemo” for “chemical” and “synthesis” for “to make.” Its function is similar to that of photosynthesis, which also turns inorganic matter into organic matter – but uses the energy of sunlight, instead of chemical energy to do so.
Today chemosynthesis is used by microbes such as bacteria and archaea. Because chemosynthesis alone is less efficient than photosynthesis or cellular respiration, it cannot be used to power complex multicellular organisms.
A few multicellular organisms live in symbiotic relationships with chemosynthetic bacteria, making them a partial energy source. Giant tube worms, for example, host chemosynthetic bacteria which supply them with sugars and amino acids.
However, these tube worms are partially dependent on photosynthesis because they use oxygen (a product of photosynthetic organisms) to make their chemosynthesis more efficient.
Chemosynthesis Equation
There are many different ways to achieve chemosynthesis. The equation for chemosynthesis will look different depending on which chemical energy source is used. However, all equations for chemosynthesis typically include:
Reactants:
- A carbon-containing inorganic compound, such as carbon dioxide or methane. This will be the source of the carbon in the organic molecule at the end of the process.
- A chemical source of energy such as hydrogen gas, hydrogen sulfide, or ferrous iron.
Products:
- An organic compound such as a sugar or amino acid.
- A transformed version of the energy source, such as elemental sulfur or ferric iron.
A commonly used example equation for chemosynthesis shows the transformation of carbon dioxide into sugar with the help of hydrogen sulfide gas:
12H2S + 6CO2 → C6H12O6 (SUGAR MOLECULE) + 6H2O + 12S
This equation is sometimes reduced to its simplest possible ratio of ingredients. This shows the relative proportions of each ingredient necessary for the reaction, although it does not capture the full quantity of hydrogen sulfide and carbon dioxide necessary to create a single sugar molecule.
The reduced version looks like this:
2H2S + CO2 → CH2O (SUGAR MOLECULE) + H2O + 2S
Function of Chemosynthesis
Chemosynthesis allows organisms to live without using the energy of sunlight or relying on other organisms for food.
Like chemosynthesis, it allows living things to make more of themselves. By turning inorganic molecules into organic molecules, the processes of chemosynthesis turn nonliving matter into living matter.
Today it is used by microbes living in the deep oceans, where no sunlight penetrates; but it is also used by some organisms living in sunny environments, such as iron bacteria and some soil bacteria.
Some scientists believe that chemosynthesis might be used by life forms in sunless extraterrestrial environments, such as in the oceans of Europa or underground environments on Mars.
It has been proposed that chemosynthesis might actually have been the first form of metabolism on Earth, with photosynthesis and cellular respiration evolving later as life forms became more complex. We may never know for sure if this is true, but some scientists believe it’s interesting to consider whether sunlight or chemical energy was the first fuel for life on Earth.
Types of Chemosynthetic Bacteria
Sulfur Bacteria
The example equation for chemosynthesis given above shows bacteria using a sulfur compound as an energy source.
The bacteria in that equation consumes hydrogen sulfide gas (12H2S), and then produces solid, elemental sulfur as a waste product (12S).
Some bacteria that use chemosynthesis use elemental sulfur itself, or more complex sulfur compounds as fuel sources, instead of hydrogen sulfide.
Metal Ion Bacteria
The most well-known type of bacteria that use metal ions for chemosynthesis are iron bacteria.
Iron bacteria can actually pose a problem for water systems in iron-rich environments, because they consume dissolved metal ions in soil and water – and produce insoluble clumps of rust-like ferric iron, which can stain plumbing fixtures and even clog them up.
However, iron bacteria are not the only organisms that use metal ions as an energy source for chemosynthesis. Other types of bacteria use arsenic, manganese, or even uranium as sources of electrons for their electron transport chains!
Nitrogen Bacteria
Nitrogen bacteria are any bacteria that use nitrogen compounds in their metabolic process. While all of these bacteria use electrons from nitrogen compounds to create organic compounds, they can have very different effects on their ecosystem depending on what compounds they use.
Nitrogen bacteria can usually be divided into three classes:
1. Nitrifying bacteria:
Nitrifying bacteria grow in soils that contain ammonia. Ammonia is an inorganic nitrogen compound that is toxic to most plants and animals – but nitrifying bacteria can use it for food, and even turn it into a beneficial substance.
Nitrifying bacteria takes electrons from ammonia and converts the ammonia into nitrites, and ultimately nitrates. Nitrates are essential for many ecosystems because most plants need them to produce essential amino acids.
Nitrification is often a two-step process: one bacteria will convert ammonia into a nitrite, and then another bacteria species will convert that nitrite into a nitrate.
Nitrifying bacteria can turn otherwise hostile soils into fertile grounds for plants, and subsequently for animals.
2. Denitrifying bacteria:
Denitrifying bacteria use nitrate compounds as their source of energy. In the process, they break these compounds down into forms that plants and animals cannot use.
This means that denitrifying bacteria can be a very big problem for plants and animals – most plant species need nitrates in the soil in order to produce essential proteins for themselves, and for the animals that eat them.
Denitrifying bacteria compete for these compounds, and can deplete soil, resulting in limited ability for plants to grow.
3. Nitrogen fixing bacteria:
These bacteria are very beneficial to ecosystems, including human agriculture. They can turn nitrogen gas – which makes up most of our atmosphere – into nitrates that plants can use to make essential proteins.
Historically, fertility issues and even famine have happened when soil became depleted of nitrates due to natural processes or overuse of farmland.
Many cultures learned to keep soil fertile by rotating nitrogen-consuming crops with nitrogen-fixing crops.
The secret of nitrogen-fixing crops is that the plants themselves do not fix nitrogen: instead, they have symbiotic relationships with nitrogen-fixing bacteria. These bacteria often grow in colonies around the plants’ roots, releasing nitrates into the surrounding soil.
The image below shows the roots of a “nitrogen-fixing plant” – note the round nodules which are, in fact, colonies of nitrogen-fixing chemosynthetic bacteria:
Modern fertilizers are often made of artificial nitrates, like those compounds made by nitrogen fixing bacteria.
Methanobacteria
Methanobacteria are actually archaeabacteria – but scientists began studying them long before they fully understood the differences between archaeabacteria and “true bacteria.”
Both archaeabacteria and true bacteria are single-celled prokaryotes – which means they look pretty similar under the microscope. But modern methods of genetic and biochemical analysis have revealed that there are important chemical differences between the two, with archaeabacteria using many chemical compounds and possessing many genes not found in the bacteria kingdom.
One of the abilities found in archaeabacteria that is not found in “true bacteria” is the metabolic process that creates methane. Only archaeabacteria species can combine carbon dioxide and hydrogen to produce methane.
Methanobacteria live in a variety of environments – including inside your own body! Methanobacteria are found at the bottom of the ocean, in swamps and wetlands, in the stomachs of cows – and even inside human stomachs, where they break down some sugars we cannot digest in order to produce methane and energy.
Related Biology Terms
- Archaeabacteria – An ancient lineage of prokaryotes. Once thought to be a sub-type of bacteria, modern analysis has revealed that archaeabacteria are an entirely different lineage from modern bacteria.
- Bacteria – A modern kingdom of prokaryotes. Today, they are sometimes called “eubacteria” or “true bacteria” to differentiate them from archaeabacteria.
- Electron transport chain – A principle often used by cells to harvest energy from the environment. Electrons are passed through a series of proteins, which harvest their energy to produce life-giving molecules such as ATP.
Quiz
1. Which of the following is NOT true of chemosynthesis?
A. It is the process of using energy from chemicals to create organic compounds.
B. It cannot be completed without energy from sunlight.
C. It uses an electron transport chain to extract energy from electrons.
D. It requires both a starting carbon compound, and a source of chemical energy.
A. It is the process of using energy from chemicals to create organic compounds.
B. It cannot be completed without energy from sunlight.
C. It uses an electron transport chain to extract energy from electrons.
D. It requires both a starting carbon compound, and a source of chemical energy.
2. Which of the following is NOT true of the equation of chemosynthesis?
A. It requires a carbon-containing inorganic compound, such as carbon dioxide, on the reactant side.
B. It requires a source of chemical energy on the reactant side.
C. It ends with an organic molecule, such as a sugar, on the product side.
D. It ends with a transformed version of the chemical energy source on the product side.
E. None of the above.
A. It requires a carbon-containing inorganic compound, such as carbon dioxide, on the reactant side.
B. It requires a source of chemical energy on the reactant side.
C. It ends with an organic molecule, such as a sugar, on the product side.
D. It ends with a transformed version of the chemical energy source on the product side.
E. None of the above.
3. Which of the following is NOT a type of chemosynthetic bacteria?
A. Iron bacteria
B. Methane-producing bacteria
C. Sulfur bacteria
D. Nitrogen-fixing bacteria
E. None of the above.
A. Iron bacteria
B. Methane-producing bacteria
C. Sulfur bacteria
D. Nitrogen-fixing bacteria
E. None of the above.
Chemosynthesis is a metabolic pathway used by some bacteria to synthesize new organic compounds such as carbohydrates by using energy derived from the oxidation of inorganic molecules—hydrogen sulfide (H2S) or ammonia (NH3). Chemosynthesis can occur in environments such as the deep ocean around hydrothermal vents , where sunlight does not penetrate, but where chemicals like hydrogen sulfide are available. Chemosynthesis is also a critical part of the nitrogen cycle , where bacteria that live in the soil , or in special plant structures called heterocysts, utilize ammonia for energy and produce nitrates and nitrites which can subsequently be used as nutrients for plants. Some bacteria can also utilize hydrogen gas (H2) and carbon dioxide (CO2) in a chemosynthetic pathway that results in the production of new organic compounds and methane (CH4).
Introduction
The struggle for food is one of the most important and complex activities to occur in an ecosystem. To help simplify and understand the production and distribution of food within a community, scientists often construct a food web, a diagram that assigns species to generalized, interlinked feeding levels. Each layer of the web represents a particular role in the movement of organic energy through the community.
Despite their unusual nature, faunas based on chemosynthesis are tied together by food webs similar to those of better-known communities. The hydrothermal vent food web below has four layers:
- Primary producers are the original source of food in the vent ecosystem, using chemical energy to create organic molecules. All other life depends on primary producers, and they have the greatest biomass in the community.
- Primary consumers get their energy directly from the primary producers by eating or living symbiotically with them.
- First order carnivores prey on the primary consumers and in turn are eaten by other animals.
- Top order carnivores eat other consumers and carnivores but are rarely hunted by other creatures. Because they are separated from the primary food production by several layers, top order carnivores have the smallest biomass in the food web.
Instructions
You will reconstruct a hydrothermal vent fauna food web on the diagram below. Click on the name of each animal to bring up its photograph and description. Then drag the name to the appropriate web layer. Once you have filled in all the spots in the food web, click on the “Show Food Web” button to see how these animals interact.