Chemosynthetic Bacteria - Definition, Examples, Pathways and Processes (2023)

Definition: What are chemosynthetic bacteria?

Basically, chemosynthetic bacteria include a group ofautotrophsBacteria that use chemical energy to produce their own food. asPhotosynthetic bacteria, chemosynthetic bacteria require a carbon source (such as carbon dioxide) and energy to produce their own food.

Most of these bacteria are aerobic and therefore rely on oxygen to successfully complete the process. However, some species (e.g. Sulfuricurvum kujiense) have been associated with anaerobic chemosynthesis.

Due to their ability to use chemical energy to produce their own food, these organisms can survive in a variety of habitats/environments, including harsh environments as extreme conditions for free-living organisms, or with other biomes through symbiosis with other organisms.

*not likephotosynthesisthis is ineukaryoticorganism iCyanobacteria, the main chemical synthesis reactionprokaryoticmicroorganisms (especiallybacteriaIarheja)

Examples of chemosynthetic bacteria include:

• Viper Butterfly
• Begiato
• T. neapolitanus
• T. novellus
• iron oxidizer

Types of Chemosynthetic Bacteria

As mentioned earlier, chemosynthesis allows different types of bacteria (chemosynthetic bacteria) to survive without relying on light energy or food from other organisms.

Here, the energy used to produce food materials is obtained from various inorganic chemicals and various chemical reactions. For this reason, there are different types of chemosynthetic bacteria, depending on the type of compound they use as an energy source.

*Some chemosynthetic bacteria live in sunny environments and are therefore exposed to sunlight. However, they do not rely on sunlight for energy

Sulfur bacteria- These bacteria (eg Paracoccus) oxidize sulfur compounds such as hydrogen sulfide (sulfide), thiosulfate and inorganic sulfur. Depending on the type of organism or sulfur compound used, the oxidation process takes place in several stages.

For example, in some organisms, inorganic sulfur will be stored until needed.

Nitrogenous bacteria- They are divided into three groups, including nitrifying bacteria, denitrifying bacteria andAzotobacter.In the case of nitrifying bacteria, ammonia is first oxidized to hydroxylaminecytoplasm(using ammonium monooxygenase).

Hydroxylamine is then oxidized by hydroxylamine oxidoreductase to produce nitrite in the periplasm. This process produces a proton (one proton per ammonium molecule). In contrast to nitrifying bacteria, denitrifying bacteria oxidize nitrate compounds as an energy source.

Methanogens/ methane bacteria- This is especially common among chemosynthetic archaea, although some scientists believe that certain bacteria use methane as an energy source for chemosynthesis.

hydrogen bacteria- Bacteria such as Hydrogenvibrio marinus and Helicobacter pylori oxidize hydrogen gas as an energy source under microaerophilic conditions.

It turns out that most of them are bacteriaanaerobicTherefore thrives in areas with little or no oxygen. This is mainly due to the fact that the enzymes (hydrogenases) used for oxidation purposes work efficiently under anaerobic conditions.

iron bacteria- Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans are some bacteria that oxidize iron. It has been shown that this process occurs under different conditions depending on the organism (e.g. low pH and aerobic-anoxic).

During chemosynthesis, chemosynthetic bacteria, which do not perform photosynthesis, must rely on the energy generated by oxidation of these compounds (inorganic substances) to produce food (sugars), while nitrogen-fixing bacteria convert nitrogen gas into nitrate. All these processes are used to generate protons which are used to fix carbon dioxide.

Typically, these reactions occur in the cytoplasm in the presence of membrane-bound respiratory enzymes. For example, in the case of hydrogen oxidation, group 1 NiFe hydrogenases located in the cytoplasm catalyze a reaction that generates 2 electrons and a proton (positively charged hydrogen) from hydrogen molecules (H2 <> 2H+ and 2e-). These electrons are then directed to the quinone pool in the electron transport chain.

In the case of hydrogen sulfide, the compound undergoes oxidation releasing electrons and hydrogen ions (called protons because they are separated from the compound and electrons and are positively charged). Therefore, the products of this reaction are sulfur, electrons and protons. Electrons and protons then enter the electron transport chain (on the membrane).

As electrons enter this chain, protons are pumped out of the battery. On the other hand, electrons are accepted by oxygen and attract protons (hydrogen ions), thus forming water molecules. Through an enzyme called ATP synthase, protons previously pumped out of the cell are directed back into the cell where their energy (kinetic energy) is stored as ATP and used to synthesize sugar.

Carbon assimilation (fixation) in chemosynthetic bacteria

Depending on the type of bacteria, their habitat and carbon source, there are many metabolic pathways for fixation.

Some of the most common routes include:

Calvin-Bensonoff cycle- In this cycle, the enzyme RuBisCo (ribulose 1,5-bisphosphate carboxylase/oxygenase) helps to add molecular carbon dioxide to ribulose 1,5-bisphosphate. This process produces a compound with six carbon atoms, which in turn converts into two molecules of 3-PGA (3-phosphoglycerate). This process is called carbon fixation because it involves converting carbon dioxide into organic molecules.

Through the energy stored in ATP and NADPH (generated by the oxidation process), the carbon compound (3-PGA) is converted back to another carbon compound during the reduction phase, forming G3P (glyceraldehyde 3-phosphate).

When one of these molecules leaves the Calvin chain (forming a carbohydrate/sugar molecule), the other participates in the formation of RuBP.

reverse Krebs cycle- Carbon fixation in the reverse Krebs cycle leads to the production of pyruvate compared to the Calvin cycle. Also known as the tricarboxylic acid reduction cycle, this cycle begins with the fixation of two carbon dioxide molecules. This leads to the production of acetyl-CoA (acetyl-CoA), which in turn is reductively carboxylated to produce pyruvate.

The pyruvate produced by this process is then used to synthesize organic cellular material.

Some other processes used by these bacteria include:

·3-hydroxypropionic acid cycle- Also known as the 3-hydroxypropionate cycle, this pathway fixes carbon dioxide in the form of malyl-CoA in the presence of acetyl-CoA and propionyl-CoA carboxylase. It is then broken down to produce acetyl-CoA and glyoxylate. Ultimately, this pathway leads to the production of pyruvate, which is used to synthesize various organic substances needed by cells.

·Reduced Acetyl-CoA- In this pathway, two carbon dioxide molecules are fixed and form acetyl-CoA. Typically, hydrogen acts as the electron donor and carbon dioxide is the electron acceptor in this reaction.

·Ciklus dikarboxilata/4-hydroxybutyric acid- This cycle is common among bacteria found in anaerobic and microaerophilic habitats (eg Desulfococcus). Like the 3-hydroxypropionate/4-hydroxybutyrate cycle, this cycle converts cetyl-CoA and two carbon molecules to succinyl-CoA (CoA). Some of the enzymes involved in this cycle include pyruvate synthase and phosphoenolpyruvate (PEP) carboxylase.

The importance of chemosynthetic bacteria

Basically, chemosynthesis refers to the process by which chemosynthetic bacteria use chemical energy to process food. Therefore, these organisms do not depend on light energy for production in contrast to photosynthesis. This makes them important primary producers in a variety of habitats that contain oxidants such as nitrates and sulfates.

For example, in deep-sea vent ecosystems, no sunlight means no photosynthesis. Since some bacteria are able to produce food through chemosynthesis, they play an important producer role in this ecosystem.

This behavior has also been shown to benefit other organisms through symbiotic relationships. For example, in different environments, nitrogen-fixing bacteria have been shown to form symbiotic relationships that benefit a variety of organisms (algae,diatoms, beans, sponges, etc.). Here, they can convert nitrogen (which is abundant in nature) into a usable form.

Here, these bacteria can catalyze atmospheric nitrogen to produce ammonia (using an enzyme called nitrogenase), which is then used by plants to synthesize nitrogen-containing biomolecules.

Another symbiotic relationship between tubeworms (Riftia pachyptila) and chemosynthetic bacteria in hydrothermal vents has received considerable attention. In this environment, the water temperature is very high due to geothermal heat. Also, these worms live at the bottom of the ocean (an environment devoid of light energy).

Despite this unfavorable environmental condition (extremely high temperature and lack of light), the availability of hydrogen sulfide enabled the bacteria to perform chemosynthesis.

Using highly vascularized gill-like plumes, the worms can absorb dissolved carbon dioxide, oxygen, and hydrogen sulfide (the hemoglobin of these organisms is capable of binding oxygen and sulfide). They are then transported into specialized cells called bacterial cells, which house the chemosynthetic bacteria.

Using sulfide and oxygen, the bacteria produce energy (ATP), which is then used to convert carbon dioxide into sugar. Then it uses these sugarsmolluskas a food source.

This symbiotic relationship has also been identified as:

• Solemid and lucinid bivalves
• well
• ciliated protists
• sea ​​sponge
• Mussels

Some characteristics associated with symbionts (chemosynthetic bacteria) include:

·havegram negativeenvelope

·They vary in form, from small spherical endosymbionts ~0.25 µm in diameter to relatively large (~10 µm long) rod-shaped chemotrophic bacteria

·Depending on the species, they can be endosymbionts or simply attach to the surface of the host body

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reference

Colleen M. Cavanaugh, Zoe P. Mckiness, Irene L.G. Newton, and Frank Stewart. (2006). Morske kemosintetske simbioze.

H.W. Annash. (1985). Chemosynthetic life support and microbial diversity in deep-sea hydrothermal vents.

Jennifer Wernegreen. (2013). endosymbiosis.

Zoran Minic and Premila D. Thongbam. (2011). Biological deep-sea hydrothermal vents as a model for studying carbon dioxide capture enzymes.

Link

https://ocw.mit.edu/high-school/biology/exam-prep/cellular-energetics/photosynthesis/chemosynthesis/

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