Photoheterotroph

Photoheterotrophs (Gk: photo = light, hetero = (an)other, troph = nourishment) 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.[1] Recent research has indicated that the oriental hornet and some aphids may be able to use light to supplement their energy supply.[2]

Metabolism

Photoheterotrophs generate ATP using light, in one of two ways:[3][4] they use a bacteriochlorophyll-based reaction center, or they use a bacteriorhodopsin. The chlorophyll-based mechanism is similar to that used in photosynthesis, where light excites the molecules in a reaction center and causes a flow of electrons through an electron transport chain (ETS). This flow of electrons through the proteins causes hydrogen ions to be pumped across a membrane. The energy stored in this proton gradient is used to drive ATP synthesis. Unlike in photoautotrophs, the electrons flow only in a cyclic pathway: electrons released from the reaction center flow through the ETS and return to the reaction center. They are not utilized to reduce any organic compounds. Purple non-sulfur bacteria, green non-sulfur bacteria and heliobacteria are examples of bacteria that carry out this scheme of photoheterotrophy.

Other organisms, including halobacteria and flavobacteria[5] and vibrios[6] have purple-rhodopsin-based proton pumps that supplement their energy supply. The archaeal version is called bacteriorhodopsin, while the eubacterial version is called proteorhodopsin. The pump consists of a single protein bound to a Vitamin A derivative, retinal. The pump may have accessory pigments (e.g., carotenoids) associated with the protein. When light is absorbed by the retinal molecule, the molecule isomerises. This drives the protein to change shape and pump a proton across the membrane. The hydrogen ion gradient can then be used to generate ATP, transport solutes across the membrane, or drive a flagellar motor. One particular flavobacterium cannot reduce carbon dioxide using light, but uses the energy from its rhodopsin system to fix carbon dioxide through anaplerotic fixation.[5] The flavobacterium is still a heterotroph as it needs reduced carbon compounds to live and cannot subsist on only light and CO2. It cannot carry out reactions in the form of

n CO2 + 2n H2D + photons(CH2O)n + 2n D + n H2O,

where H2D may be water, H2S or another compound/compounds providing the reducing electrons and protons; the 2D + H2O pair represents an oxidized form.

However, it can fix carbon in reactions like:

CO2 + pyruvate + ATP (from photons) → malate + ADP +Pi

where malate or other useful molecules are otherwise obtained by breaking down other compounds by

carbohydrate + O2 → malate + CO2 + energy.

This method of carbon fixation is useful when reduced carbon compounds are scarce and cannot be wasted as CO2 during interconversions, but energy is plentiful in the form of sunlight.

Flowchart

Troph flowchart
Flowchart to determine if a species is autotroph, heterotroph, or a subtype

See also

References

  1. ^ D.A. Bryant & N.-U. Frigaard (November 2006). "Prokaryotic photosynthesis and phototrophy illuminated". Trends Microbiol. 14 (11): 488–96. doi:10.1016/j.tim.2006.09.001. PMID 16997562.
  2. ^ Valmalette, J. C.; Dombrovsky, A.; Brat, P.; Mertz, C.; Capovilla, M.; Robichon, A. (2012). "Light- induced electron transfer and ATP synthesis in a carotene synthesizing insect". Scientific Reports. 2: 579. doi:10.1038/srep00579. PMC 3420219. PMID 22900140.
  3. ^ Bryant, Donald A.; Niels-Ulrik Frigaard (November 2006). "Prokaryotic photosynthesis and phototrophy illuminated". Trends in Microbiology. 14 (11): 488–496. doi:10.1016/j.tim.2006.09.001. ISSN 0966-842X. PMID 16997562.
  4. ^ Zubkov, Mikhail V (2009-09-01). "Photoheterotrophy in Marine Prokaryotes". Journal of Plankton Research. 31 (9): 933–938. doi:10.1093/plankt/fbp043. ISSN 0142-7873. Retrieved 2012-03-30.
  5. ^ a b González, José M; Beatriz Fernández-Gómez; Antoni Fernàndez-Guerra; Laura Gómez-Consarnau; Olga Sánchez; Montserrat Coll-Lladó; Javier Del Campo; Lorena Escudero; Raquel Rodríguez-Martínez; Laura Alonso-Sáez; Mikel Latasa; Ian Paulsen; Olga Nedashkovskaya; Itziar Lekunberri; Jarone Pinhassi; Carlos Pedrós-Alió (2008-06-24). "Genome Analysis of the Proteorhodopsin-Containing Marine Bacterium Polaribacter Sp. MED152 (Flavobacteria)". Proceedings of the National Academy of Sciences. 105 (25): 8724–8729. doi:10.1073/pnas.0712027105. ISSN 0027-8424. PMC 2438413. PMID 18552178.
  6. ^ Gómez-Consarnau, Laura; Neelam Akram; Kristoffer Lindell; Anders Pedersen; Richard Neutze; Debra L. Milton; José M. González; Jarone Pinhassi (2010). "Proteorhodopsin Phototrophy Promotes Survival of Marine Bacteria during Starvation". PLoS Biol. 8 (4): e1000358. doi:10.1371/journal.pbio.1000358. PMC 2860489. PMID 20436956.

Sources

University of Wisconsin, Madison Microbiology Online Textbook

AAPB

AAPB may refer to:

Aerobic anoxygenic photoheterotroph bacteria

Aerobic anoxygenic phototrophic bacteria

American Archive of Public Broadcasting

American Association of Pathologists and Bacteriologists

Association for Applied Psychophysiology and Biofeedback

Aerobic anoxygenic photoheterotroph bacteria

Aerobic anoxygenic photoheterotrophic bacteria (AAPB), also named aerobic anoxygenic photoheterotrophs (AAPs), is a group of bacteria that are primarily heterotrophic but can utilize light energy through bacterial chlorophyll a.

Autotroph

An autotroph or primary producer, is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) from simple substances present in its surroundings, generally using energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis). They are the producers in a food chain, such as plants on land or algae in water (in contrast to heterotrophs as consumers of autotrophs). They do not need a living source of energy or organic carbon. Autotrophs can reduce carbon dioxide to make organic compounds for biosynthesis and also create a store of chemical energy. Most autotrophs use water as the reducing agent, but some can use other hydrogen compounds such as hydrogen sulfide. Some autotrophs, such as green plants and algae, are phototrophs, meaning that they convert electromagnetic energy from sunlight into chemical energy in the form of reduced carbon.

Autotrophs can be photoautotrophs or chemoautotrophs. Phototrophs use light as an energy source, while chemotrophs use electron donors as a source of energy, whether from organic or inorganic sources; however in the case of autotrophs, these electron donors come from inorganic chemical sources. Such chemotrophs are lithotrophs. Lithotrophs use inorganic compounds, such as hydrogen sulfide, elemental sulfur, ammonium and ferrous iron, as reducing agents for biosynthesis and chemical energy storage. Photoautotrophs and lithoautotrophs use a portion of the ATP produced during photosynthesis or the oxidation of inorganic compounds to reduce NADP+ to NADPH to form organic compounds.

Chemotroph

Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs). The chemotroph designation is in contrast to phototrophs, which use solar energy. Chemotrophs can be either autotrophic or heterotrophic. Chemotrophs are found in ocean floors where sunlight cannot reach them because they are not dependent on solar energy. Ocean floors often contain underwater volcanos that can provide heat as a substitute for sunlight's warmth.

Congregibacter litoralis

Congregibacter litoralis KT71 is a gram-negative Gammaproteobacteria part of the NOR5/OM60 Clade discovered in seawater from Heligoland, an island in the North Sea by H. Eilers from the Max Planck Institute for Microbiology. C. litoralis KT71 is described as a pleomorphic bacterium and has a size of 2 x 0.5 μm. When grown in culture, C. litoralis KT71 has a generation time of 4.5 hours and prefers to grow on complex substrates where the sole carbon source is undefined, though it can utilize some sole carbon sources because they are most likely used by the organism for its central metabolism.

Dinoroseobacter shibae

Dinoroseobacter shibae is a facultative anaerobic anoxygenic photoheterotroph belonging to the family, Rhodobacteraceae. First isolated from washed cultivated dinoflagellates, they have been reported to have mutualistic as well as pathogenic symbioses with dinoflagellates.

Erythrobacter longus

Erythrobacter longus is a species of bacteria, the genus' type species. It contains bacteriochlorophyll a. It is motile by means of subpolar flagella. Its type strain is OCh101 (= IFO 14126).

Heterotroph

A heterotroph (; Ancient Greek ἕτερος héteros = "other" plus trophe = "nutrition") is an organism that cannot produce its own food, relying instead on the intake of nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but not producers. Living organisms that are heterotrophic include all animals and fungi, some bacteria and protists, and parasitic plants. The term heterotroph arose in microbiology in 1946 as part of a classification of microorganisms based on their type of nutrition. The term is now used in many fields, such as ecology in describing the food chain.

Heterotrophs may be subdivided according to their energy source. If the heterotroph uses chemical energy, it is a chemoheterotroph (e.g., humans and mushrooms). If it uses light for energy, then it is a photoheterotroph (e.g., green non-sulfur bacteria).

Heterotrophs represent one of the two mechanisms of nutrition (trophic levels), the other being autotrophs (auto = self, troph = nutrition). Autotrophs use energy from sunlight (photoautotrophs) or inorganic compounds (lithoautotrophs) to convert inorganic carbon dioxide to organic carbon compounds and energy to sustain their life. Comparing the two in basic terms, heterotrophs (such as animals) eat either autotrophs (such as plants) or other heterotrophs, or both.

Detritivores are heterotrophs which obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). Saprotrophs (also called lysotrophs) are chemoheterotrophs that use extracellular digestion in processing decayed organic matter. It is a term most often associated with fungi. The process is most often facilitated through the active transport of such materials through endocytosis within the internal mycelium and its constituent hyphae.

List of Greek and Latin roots in English/P–Z

The following is an alphabetical list of Greek and Latin roots, stems, and prefixes commonly used in the English language from P to Z. See also the lists from A to G and from H to O.

Some of those used in medicine and medical technology are not listed here but instead in the entry for List of medical roots, suffixes and prefixes.

Phototroph

Phototrophs (Gr: φῶς, φωτός = light, τροϕή = nourishment) are the organisms that carry out photon capture to acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a common misconception that phototrophs are obligatorily photosynthetic. Many, but not all, phototrophs often photosynthesize: they anabolically convert carbon dioxide into organic material to be utilized structurally, functionally, or as a source for later catabolic processes (e.g. in the form of starches, sugars and fats). All phototrophs either use electron transport chains or direct proton pumping to establish an electro-chemical gradient which is utilized by ATP synthase, to provide the molecular energy currency for the cell. Phototrophs can be either autotrophs or heterotrophs. As their electron and hydrogen donors are inorganic compounds [Na2S2O3 (PSB) and H2S (GSB)] they can be also called as lithotrophs, and so, some photoautotrophs are also called photolithoautotrophs. Examples of phototroph organisms: Rhodobacter capsulatus, Chromatium, Chlorobium etc.

Rhodomicrobium vannielii

Rhodomicrobium vannielii is a non-sulphur, photoheterotroph bacterium. Rhodomicrobium vannielii produces acyclic and aliphatic cyclic carotenoids like anhydrorhodovibrin, rhodovibrin, spirilloxanthin and rhodopin.

Streamlining theory

Genomic streamlining is a theory in evolutionary biology and microbial ecology that suggests that there is a reproductive benefit to prokaryotes having a smaller genome size with less non-coding DNA and fewer non-essential genes. There is a lot of variation in prokaryotic genome size, with the smallest free-living cell's genome being roughly ten times smaller than the largest prokaryote. Two of the bacterial taxa with the smallest genomes are Prochlorococcus and Pelagibacter ubique, both highly abundant marine bacteria commonly found in oligotrophic regions. Similar reduced genomes have been found in uncultured marine bacteria, suggesting that genomic streamlining is a common feature of bacterioplankton. This theory is typically used with reference to free-living organisms in oligotrophic environments.

General
Producers
Consumers
Decomposers
Microorganisms
Food webs
Example webs
Processes
Defense,
counter
Ecology: Modelling ecosystems: Other components
Population
ecology
Species
Species
interaction
Spatial
ecology
Niche
Other
networks
Other

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.