Rhodopseudomonas palustris
Encyclopedia
Rhodopseudomonas palustris is a gram-negative
purple non-sulfur bacteria, notable for its ability to switch between four different modes of metabolism.
R. palustris has been found to grow in swine waste lagoons, earthworm droppings, marine coastal sediments and pond water. Although purple non-sulfur bacteria are normally photoheterotrophic, R. palustris has the ability to switch between the four different modes of metabolism that support life: photoautotrophic, photoheterotroph
ic, chemoautotroph and chemoheterotrophic. This means that this bacterium can grow with or without oxygen
; it can use light, inorganic compounds, or organic compounds for energy; it can acquire carbo
n from either carbon dioxide fixation or green plant-derived compounds; and it can also fix nitrogen
. This metabolic versatility has raised interest in the research community and makes this bacterium suitable for potential use in biotechnological
applications.
Efforts are currently being made to understand how this organism integrates the various metabolic modules in response to environmental changes. The complete genome of the strain Rhodopseudomonas palustris CGA009 was sequenced (List of sequenced bacterial genomes) in the hope of getting more information about how the bacterium senses environmental changes and how it regulates its metabolic pathways accordingly. It was found that R. palustris has genes that encode for proteins that make up light-harvesting complex
es and photosynthetic reaction centre
s. Light-harvesting complexes and photosynthetic reaction centers are typically found in photosynthetic organisms like green plants. Besides being a photosynthetic bacteria R. palustris can modulate photosynthesis
according to the amount of light available. For instance, in low-light circumstances it responds by increasing the level of these light-harvesting (LH) complexes that allow light absorption.
R. palustris also has genes
that encode for the protein RubisCO
, an enzyme that is necessary for carbondioxide fixation (see Carbon fixation
) found in plants and other photosynthetic organisms. The genome reveals also the existence of proteins involved in nitrogen fixation
(see Diazotroph
).
Purple photorophic bacteria are of great interest due to their use in biotechnological applications. These bacteria can be used for 'bioplastic' synthesis and hydrogen
production. R. palustris differs from other purple bacteria due to is ability to modulate photosynthesis according to the amount of light available and its ability to degrade aromatic compounds found in agricultural and industrial waste. It also has the unique characteristic of encoding for a vanadium-containing
nitrogenase
, which produces as a byproduct of nitrogen fixation three times more hydrogen than the nitrogenase of other bacteria (molybennum-containing nitrogenase). The potential to manipulate R. palustris to be used as hydrogen production source and biodegradation still requires more detailed knowledge of its metabolic pathways and regulation mechanisms.
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
purple non-sulfur bacteria, notable for its ability to switch between four different modes of metabolism.
R. palustris has been found to grow in swine waste lagoons, earthworm droppings, marine coastal sediments and pond water. Although purple non-sulfur bacteria are normally photoheterotrophic, R. palustris has the ability to switch between the four different modes of metabolism that support life: photoautotrophic, photoheterotroph
Heterotroph
A heterotroph is an organism that cannot fix carbon and uses organic carbon for growth. This contrasts with autotrophs, such as plants and algae, which can use energy from sunlight or inorganic compounds to produce organic compounds such as carbohydrates, fats, and proteins from inorganic carbon...
ic, chemoautotroph and chemoheterotrophic. This means that this bacterium can grow with or without oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
; it can use light, inorganic compounds, or organic compounds for energy; it can acquire carbo
Carbo
Carbo was a plebeian family within the gens Papiria of ancient Rome. Several members were notable:* Gaius Papirius Carbo, praetor 168 BC* Gaius Papirius Carbo, consul 120 BC* Gnaeus Papirius Carbo, consul 113 BC...
n from either carbon dioxide fixation or green plant-derived compounds; and it can also fix nitrogen
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
. This metabolic versatility has raised interest in the research community and makes this bacterium suitable for potential use in biotechnological
Biotechnology
Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...
applications.
Efforts are currently being made to understand how this organism integrates the various metabolic modules in response to environmental changes. The complete genome of the strain Rhodopseudomonas palustris CGA009 was sequenced (List of sequenced bacterial genomes) in the hope of getting more information about how the bacterium senses environmental changes and how it regulates its metabolic pathways accordingly. It was found that R. palustris has genes that encode for proteins that make up light-harvesting complex
Light-harvesting complex
A light-harvesting complex is a complex of subunit proteins that may be part of a larger supercomplex of a photosystem, the functional unit in photosynthesis. It is used by plants and photosynthetic bacteria to collect more of the incoming light than would be captured by the photosynthetic reaction...
es and photosynthetic reaction centre
Photosynthetic reaction centre
A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors assembled together to execute the primary energy conversion reactions of photosynthesis...
s. Light-harvesting complexes and photosynthetic reaction centers are typically found in photosynthetic organisms like green plants. Besides being a photosynthetic bacteria R. palustris can modulate photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
according to the amount of light available. For instance, in low-light circumstances it responds by increasing the level of these light-harvesting (LH) complexes that allow light absorption.
R. palustris also has genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
that encode for the protein RubisCO
RuBisCO
Ribulose-1,5-bisphosphate carboxylase oxygenase, commonly known by the shorter name RuBisCO, is an enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants to energy-rich molecules such as glucose. RuBisCo is an abbreviation...
, an enzyme that is necessary for carbondioxide fixation (see Carbon fixation
Carbon fixation
In biology, carbon fixation is the reduction of carbon dioxide to organic compounds by living organisms. The obvious example is photosynthesis. Carbon fixation requires both a source of energy such as sunlight, and an electron donor such as water. All life depends on fixed carbon. Organisms that...
) found in plants and other photosynthetic organisms. The genome reveals also the existence of proteins involved in nitrogen fixation
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
(see Diazotroph
Diazotroph
Diazotrophs are bacteria and archaea that fix atmospheric nitrogen gas into a more usable form such as ammonia.A diazotroph is an organism that is able to grow without external sources of fixed nitrogen. Examples of organisms that do this are rhizobia and Frankia and Azospirillum. All diazotrophs...
).
Purple photorophic bacteria are of great interest due to their use in biotechnological applications. These bacteria can be used for 'bioplastic' synthesis and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
production. R. palustris differs from other purple bacteria due to is ability to modulate photosynthesis according to the amount of light available and its ability to degrade aromatic compounds found in agricultural and industrial waste. It also has the unique characteristic of encoding for a vanadium-containing
Vanadium nitrogenase
Vanadium nitrogenase is a key enzyme for nitrogen fixation found in nitrogen-fixing bacteria, and is used as an alternative to molybdenum nitrogenase when molybdenum is unavailable. An important component of the nitrogen cycle, vanadium nitrogenase converts nitrogen gas to ammonia, thereby making...
nitrogenase
Nitrogenase
Nitrogenases are enzymes used by some organisms to fix atmospheric nitrogen gas . It is the only known family of enzymes that accomplish this process. Dinitrogen is quite inert because of the strength of its N-N triple bond...
, which produces as a byproduct of nitrogen fixation three times more hydrogen than the nitrogenase of other bacteria (molybennum-containing nitrogenase). The potential to manipulate R. palustris to be used as hydrogen production source and biodegradation still requires more detailed knowledge of its metabolic pathways and regulation mechanisms.