Rhodopseudomonas palustris | |
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Species: | R. palustris |
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Rhodopseudomonas palustris (Molisch 1907) van Niel 1944 | |
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Rhodopseudomonas palustris is a rod-shaped, Gram-negative purple nonsulfur bacterium, notable for its ability to switch between four different modes of metabolism. [2]
R. palustris is found extensively in nature, and has been isolated from swine waste lagoons, earthworm droppings, marine coastal sediments, and pond water. Although purple nonsulfur bacteria are normally photoheterotrophic, R. palustris can flexibly switch among any of the four modes of metabolism that support life: photoautotrophic, photoheterotrophic, chemoautotrophic, or chemoheterotrophic. [2]
R. palustris is usually found as a wad of slimy masses, and cultures appear from pale brown to peach-colored. Etymologically, rhodum is a Greek noun meaning rose, pseudes is the Greek adjective for false, and monas refers to a unit in Greek. Therefore, Rhodopseudomonas, which implies a unit of false rose, describes the appearance of the bacteria. Palustris is Latin for marshy, and indicates the common habitat of the bacterium. [3]
R. palustris can grow with or without oxygen, or it can use light or inorganic or organic compounds for energy. It can also acquire carbon from either carbon dioxide fixation or green plant-derived compounds. Finally, R. palustris is also capable of fixing nitrogen for growth. This metabolic versatility has raised interest in the research community, and it makes this bacterium suitable for potential use in biotechnological applications.
Efforts are currently being made to understand how this organism adjusts its metabolism in response to environmental changes. The complete genome of the strain Rhodopseudomonas palustris CGA009 was sequenced in 2004 (see list of sequenced bacterial genomes) to get more information about how the bacterium senses environmental changes and regulates its metabolic pathways. R. palustris can deftly acquire and process various components from its environment, as necessitated by fluctuations in the levels of carbon, nitrogen, oxygen, and light.
R. palustris has genes that encode for proteins that make up light-harvesting complexes (LHCs) and photosynthetic reaction centers. LHCs and photosynthetic reaction centers are typically found in photosynthetic organisms such as green plants. Moreover, R. palustris can modulate photosynthesis according to the amount of light available, like other purple bacteria. For instance, in low-light circumstances, it responds by increasing the level of these LHCs that allow light absorption. The wavelengths of the light absorbed by R. palustris differ from those absorbed by other phototrophs.
R. palustris also has genes that encode for the protein ruBisCO, an enzyme necessary for carbon dioxide fixation in plants and other photosynthetic organisms. The genome of CGA009 also reveals the existence of proteins involved in nitrogen fixation (see diazotroph).
In addition, this bacterium can combine oxygen-sensitive and oxygen-requiring enzyme reaction processes for metabolism, thus it can thrive under varying and even very little levels of oxygen.
The genome of R. palustris consists of a variety of genes that are responsible for biodegradation. It can metabolize lignin and acids found in degrading plant and animal waste by metabolizing carbon dioxide. [4] In addition, it can degrade aromatic compounds found in industrial waste. [5] This bacterium is an efficient biodegradation catalyst in both aerobic and anaerobic environments. [ citation needed ]
Purple phototrophic bacteria have drawn interest for their biotechnological applications. These bacteria can be used for bioplastic synthesis and hydrogen production. R. palustris has the unique characteristic of encoding for a vanadium-containing nitrogenase. It produces, as a byproduct of nitrogen fixation, three times more hydrogen than do molybdenum-containing nitrogenases of other bacteria. [2] The potential to manipulate R. palustris to be used as a reliable hydrogen production source or for biodegradation still lacks detailed knowledge of its metabolic pathways and regulation mechanisms.
A strain of R. palustris (DX-1) is one of the few microorganisms and the first Alphaproteobacteria found to generate electricity at high power densities in low-internal resistance microbial fuel cells (MFCs). [6] DX-1 produces electric current in MFCs in the absence of a catalyst, without light or hydrogen production. This strain is exoelectrogenic, meaning that it can transfer electrons outside the cell. Other microorganisms isolated from MFCs cannot produce power densities higher than mixed cultures of microbes can under the same fuel-cell conditions, but R. palustris DX-1 can produce significantly higher power densities.
This Rhodopseudomonas species is widely found in wastewaters, and DX-1 generates electricity using compounds that Rhodopseudomonas is known to degrade. Therefore, this technology can be harnessed to produce bioelectricity from biomass and for wastewater treatment. However, the energy generated through this process is currently not sufficient for large-scale wastewater treatment. [7]
A 2014 study explained the cellular processes that allow the strain R. palustris TIE-1 to obtain energy through extracellular electron transfer. [8] TIE-1 curiously takes in electrons from materials rich in iron, sulfur, and other minerals found in the sediment beneath the surface. In an extraordinary strategy, as the microbes pull electrons away from iron, iron oxide crystallizes in the soil, eventually becomes conductive, and facilitates TIE-1 in oxidizing other minerals.
TIE-1 then converts these electrons into energy using carbon dioxide as an electron receptor. A gene that produces ruBisCo helps this strain of R. palustris to achieve energy generation through electrons. TIE-1 uses ruBisCo to convert carbon dioxide into nutrition for itself. This metabolism has phototrophic aspects, since the gene and the ability to uptake electrons are stimulated by sunlight. Therefore, R. palustris TIE-1 charges itself using minerals located deep in the soil, while using light by remaining on the surface itself. The ability of TIE-1 to use electricity can be used to manufacture batteries, but its efficiency as a fuel source remains questionable, but it has possible applications in the pharmaceutical industry.
Photosynthesis is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabolism. Photosynthesis usually refers to oxygenic photosynthesis, a process that produces oxygen.
Photosynthetic organisms store the chemical energy so produced within intracellular organic compounds like sugars, glycogen, cellulose and starches. To use this stored chemical energy, an organism's cells metabolize the organic compounds through cellular respiration. Photosynthesis plays a critical role in producing and maintaining the oxygen content of the Earth's atmosphere, and it supplies most of the biological energy necessary for complex life on Earth.
Primary nutritional groups are groups of organisms, divided in relation to the nutrition mode according to the sources of energy and carbon, needed for living, growth and reproduction. The sources of energy can be light or chemical compounds; the sources of carbon can be of organic or inorganic origin.
The green sulfur bacteria are a phylum, Chlorobiota, of obligately anaerobic photoautotrophic bacteria that metabolize sulfur.
Chloroflexus aurantiacus is a photosynthetic bacterium isolated from hot springs, belonging to the green non-sulfur bacteria. This organism is thermophilic and can grow at temperatures from 35 to 70 °C. Chloroflexus aurantiacus can survive in the dark if oxygen is available. When grown in the dark, Chloroflexus aurantiacus has a dark orange color. When grown in sunlight it is dark green. The individual bacteria tend to form filamentous colonies enclosed in sheaths, which are known as trichomes.
Biological carbon fixation, or сarbon assimilation, is the process by which living organisms convert inorganic carbon to organic compounds. These organic compounds are then used to store energy and as structures for other biomolecules. Carbon is primarily fixed through photosynthesis, but some organisms use chemosynthesis in the absence of sunlight. Chemosynthesis is carbon fixation driven by chemical energy rather than from sunlight.
Purple bacteria or purple photosynthetic bacteria are Gram-negative proteobacteria that are phototrophic, capable of producing their own food via photosynthesis. They are pigmented with bacteriochlorophyll a or b, together with various carotenoids, which give them colours ranging between purple, red, brown, and orange. They may be divided into two groups – purple sulfur bacteria and purple non-sulfur bacteria. Purple bacteria are anoxygenic phototrophs widely spread in nature, but especially in aquatic environments, where there are anoxic conditions that favor the synthesis of their pigments.
The Chromatiaceae are one of the two families of purple sulfur bacteria, together with the Ectothiorhodospiraceae. They belong to the order Chromatiales of the class Gammaproteobacteria, which is composed by unicellular Gram-negative organisms. Most of the species are photolithoautotrophs and conduct an anoxygenic photosynthesis, but there are also representatives capable of growing under dark and/or microaerobic conditions as either chemolithoautotrophs or chemoorganoheterotrophs.
Photoheterotrophs are heterotrophic phototrophs—that is, they are organisms that use light for energy, but cannot use carbon dioxide as their sole carbon source. Consequently, they use organic compounds from the environment to satisfy their carbon requirements; these compounds include carbohydrates, fatty acids, and alcohols. Examples of photoheterotrophic organisms include purple non-sulfur bacteria, green non-sulfur bacteria, and heliobacteria. These microorganisms are ubiquitous in aquatic habitats, occupy unique niche-spaces, and contribute to global biogeochemical cycling. Recent research has also indicated that the oriental hornet and some aphids may be able to use light to supplement their energy supply.
Capnophiles are microorganisms that thrive in the presence of high concentrations of carbon dioxide.
Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.
Microbial fuel cell (MFC) is a type of bioelectrochemical fuel cell system also known as micro fuel cell that generates electric current by diverting electrons produced from the microbial oxidation of reduced compounds on the anode to oxidized compounds such as oxygen on the cathode through an external electrical circuit. MFCs produce electricity by using the electrons derived from biochemical reactions catalyzed by bacteria.Comprehensive Biotechnology MFCs can be grouped into two general categories: mediated and unmediated. The first MFCs, demonstrated in the early 20th century, used a mediator: a chemical that transfers electrons from the bacteria in the cell to the anode. Unmediated MFCs emerged in the 1970s; in this type of MFC the bacteria typically have electrochemically active redox proteins such as cytochromes on their outer membrane that can transfer electrons directly to the anode. In the 21st century MFCs have started to find commercial use in wastewater treatment.
Phototrophic biofilms are microbial communities generally comprising both phototrophic microorganisms, which use light as their energy source, and chemoheterotrophs. Thick laminated multilayered phototrophic biofilms are usually referred to as microbial mats or phototrophic mats. These organisms, which can be prokaryotic or eukaryotic organisms like bacteria, cyanobacteria, fungi, and microalgae, make up diverse microbial communities that are affixed in a mucous matrix, or film. These biofilms occur on contact surfaces in a range of terrestrial and aquatic environments. The formation of biofilms is a complex process and is dependent upon the availability of light as well as the relationships between the microorganisms. Biofilms serve a variety of roles in aquatic, terrestrial, and extreme environments; these roles include functions which are both beneficial and detrimental to the environment. In addition to these natural roles, phototrophic biofilms have also been adapted for applications such as crop production and protection, bioremediation, and wastewater treatment.
Many photosynthetic life forms (plants, algae, phototrophic and chemoautotrophic bacteria, and archaea) require a way to utilize carbon into their metabolic pathways. This usually occurs in pathways that fix carbon from carbon dioxide (CO2). In the 3-hydroxypropionate bicycle, photosynthetic organisms like Chloroflexus aurantiacus, fix CO2 and bicarbonate (HCO3- ) as part of their metabolic processes.
Rhodovulum sulfidophilum is a gram-negative purple nonsulfur bacteria. The cells are rod-shaped, and range in size from 0.6 to 0.9 μm wide and 0.9 to 2.0 μm long, and have a polar flagella. These cells reproduce asexually by binary fission. This bacterium can grow anaerobically when light is present, or aerobically (chemoheterotrophic) under dark conditions. It contains the photosynthetic pigments bacteriochlorophyll a and of carotenoids.
Rhodoferax is a genus of Betaproteobacteria belonging to the purple nonsulfur bacteria. Originally, Rhodoferax species were included in the genus Rhodocyclus as the Rhodocyclus gelatinous-like group. The genus Rhodoferax was first proposed in 1991 to accommodate the taxonomic and phylogenetic discrepancies arising from its inclusion in the genus Rhodocyclus. Rhodoferax currently comprises four described species: R. fermentans, R. antarcticus, R. ferrireducens, and R. saidenbachensis. R. ferrireducens, lacks the typical phototrophic character common to two other Rhodoferax species. This difference has led researchers to propose the creation of a new genus, Albidoferax, to accommodate this divergent species. The genus name was later corrected to Albidiferax. Based on geno- and phenotypical characteristics, A. ferrireducens was reclassified in the genus Rhodoferax in 2014. R. saidenbachensis, a second non-phototrophic species of the genus Rhodoferax was described by Kaden et al. in 2014.
Rhodobacter capsulatus is a species of purple bacteria, a group of bacteria that can obtain energy through photosynthesis. Its name is derived from the Latin adjective "capsulatus", itself derived Latin noun "capsula", and the associated Latin suffix for masculine nouns, "-atus".
Thiodictyon is a genus of gram-negative bacterium classified within purple sulfur bacteria (PSB).
Microbial electrochemical technologies (METs) use microorganisms as electrochemical catalyst, merging the microbial metabolism with electrochemical processes for the production of bioelectricity, biofuels, H2 and other valuable chemicals. Microbial fuel cells (MFC) and microbial electrolysis cells (MEC) are prominent examples of METs. While MFC is used to generate electricity from organic matter typically associated with wastewater treatment, MEC use electricity to drive chemical reactions such as the production of H2 or methane. Recently, microbial electrosynthesis cells (MES) have also emerged as a promising MET, where valuable chemicals can be produced in the cathode compartment. Other MET applications include microbial remediation cell, microbial desalination cell, microbial solar cell, microbial chemical cell, etc.,.
Chloroflexus aggregans is a bacterium from the genus Chloroflexus which has been isolated from hot springs in Japan.
Prosthecochloris aestuarii is a green sulfur bacterium in the genus Prosthecochloris. This organism was originally isolated from brackish lagoons located in Sasyk-Sivash and Sivash. They are characterized by the presence of "prosthecae" on their cell surface; the inner part of these appendages house the photosynthetic machinery within chlorosomes, which are characteristic structures of green sulfur bacteria. Additionally, like other green sulfur bacteria, they are Gram-negative, non-motile, and non-spore forming. Of the four major groups of green sulfur bacteria, P. aestuarii serves as the type species for Group 4.