Oligotroph

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An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates of metabolism, and generally low population density. Oligotrophic environments are those that offer little to sustain life. These environments include deep oceanic sediments, caves, glacial and polar ice, deep subsurface soil, aquifers, ocean waters, and leached soils.

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Examples of oligotrophic organisms are the cave-dwelling olm; the bacterium "Candidatus Pelagibacter communis", which is the most abundant organism in the ocean (with an estimated 2 × 1028 individuals in total); and lichens, with their extremely low metabolic rate.

Etymologically, the word "oligotroph" is a combination of the Greek adjective oligos (ὀλίγος) [1] meaning "few" and the adjective trophikos (τροφικός) [2] meaning "feeding".

Plant adaptations

Plant adaptations to oligotrophic soils provide for greater and more efficient nutrient uptake, reduced nutrient consumption, and efficient nutrient storage. Improvements in nutrient uptake are facilitated by root adaptations such as nitrogen-fixing root nodules, mycorrhizae and cluster roots. Consumption is reduced by very slow growth rates, and by efficient use of low-availability nutrients; for example, the use of highly available ions to maintain turgor pressure, with low-availability nutrients reserved for the building of tissues. Despite these adaptations, nutrient requirement typically exceed uptake during the growing season, so many oligotrophic plants have the ability to store nutrients, for example, in trunk tissues, when demand is low, and remobilise them when demand increases.

Oligotrophic environments

Oligotrophs occupy environments where the available nutrients offer little to sustain life. The term “oligotrophic” is commonly used to describe terrestrial and aquatic environments with very low concentrations of nitrates, iron, phosphates, and carbon sources. [3] [4]

Oligotrophs have acquired survival mechanisms that involve the expression of genes during periods of low nutrient conditions, which has allowed them to find success in various environments. Despite the capability to live in low nutrient concentrations, oligotrophs may find difficulty surviving in nutrient-rich environments. [3]

Antarctica

Antarctic environments offer very little to sustain life as most organisms are not well adapted to live under nutrient-limiting conditions and cold temperatures (lower than 5 °C). As such, these environments display a large abundance of psychrophiles that are well adapted to living in an Antarctic biome. Most oligotrophs live in lakes where water helps support biochemical processes for growth and survival. [5] Below are some documented examples of oligotrophic environments in Antarctica:

Lake Vostok , a freshwater lake which has been isolated from the world beneath 4 km (2.5 mi) of Antarctic ice is frequently held to be a primary example of an oligotrophic environment. [6] Analysis of ice samples showed ecologically separated microenvironments. Isolation of microorganisms from each microenvironment led to the discovery of a wide range of different microorganisms present within the ice sheet. [7] Traces of fungi have also been observed which suggests potential for unique symbiotic interactions. [8] [7] The lake’s extensive oligotrophy has led some to believe parts of the lake are completely sterile. [8] This lake is a helpful tool for simulating studies regarding extraterrestrial life on frozen planets and other celestial bodies. [9]

Crooked Lake is an ultra-oligotrophic glacial lake [10] with a thin distribution of heterotrophic and autotrophic microorganisms. [11] The microbial loop plays a big role in cycling nutrients and energy within this lake, despite particularly low bacterial abundance and productivity in these environments. [10] The little ecological diversity can be attributed to the lake's low annual temperatures. [12] Species discovered in this lake include Ochromonas, Chlamydomonas, Scourfeldia, Cryptomonas, Akistrodesmus falcatus, and Daphniopsis studeri (a microcrustacean). It is proposed that low competitive selection against Daphniopsis studeri has allowed the species to survive long enough to reproduce in nutrient limiting environments. [11]

Australia

The sandplains and lateritic soils of southern Western Australia, where an extremely thick craton has precluded any geological activity since the Cambrian and there has been no glaciation to renew soils since the Carboniferous. Thus, soils are extremely nutrient-poor and most vegetation must use strategies such as cluster roots to gain even the smallest quantities of such nutrients as phosphorus and sulfur.

The vegetation in these regions, however, is remarkable for its biodiversity, which in places is as great as that of a tropical rainforest and produces some of the most spectacular wildflowers in the world. It is however, severely threatened by climate change which has moved the winter rain belt south, and also by clearing for agriculture and through use of fertilizers, which is primarily driven by low land costs which make farming economic even with yields a fraction of those in Europe or North America.

South America

An example of oligotrophic soils are those on white-sands, with soil pH lower than 5.0, on the Rio Negro basin on northern Amazonia that house very low-diversity, extremely fragile forests and savannahs drained by blackwater rivers; dark water colour due to high concentration of tannins, humic acids and other organic compounds derived from the very slow decomposition of plant matter. [13] [14] [15] Similar forests are found in the oligotrophic waters of the Patía River delta on the Pacific side of the Andes. [16]

Ocean

In the ocean, the subtropical gyres north and south of the equator are regions in which the nutrients required for phytoplankton growth (for instance, nitrate, phosphate and silicic acid) are strongly depleted all year round. These areas are described as oligotrophic and exhibit low surface chlorophyll. They are occasionally described as "ocean deserts". [17]

Oligotrophic soil environments

The oligotrophic soil environments include agricultural soil, frozen soil, et cetera. [18] [19] Various factors, such as decomposition, soil structure, fertilization and temperature, can affect the nutrient-availability in the soil environments. [18] [19]

Generally, the nutrient becomes less available along the depth of the soil environment, because on the surface, the organic compounds decomposed from the plant and animal debris are consumed quickly by other microbes, resulting in the lack of nutrient in the deeper level of soil. [18] In addition, the metabolic waste produced by the microorganisms on the surface also causes the accumulation of toxic chemicals in the deeper area. [18] Furthermore, oxygen and water are important for some metabolic pathways, but it is difficult for water and oxygen to diffuse as the depth increases. [18] Some factors, such as soil aggregates, pores and extracellular enzymes, may help water, oxygen and other nutrients diffuse into the soil. [20] Moreover, the presence of mineral under the soil provides the alternative sources for the species living in the oligotrophic soil. [20] In terms of the agricultural lands, the application of fertilizer has a complicated impact on the source of carbon, either increasing or decreasing the organic carbon in the soil. [20]

Collimonas is one of the species that are capable of living in the oligotrophic soil. [21] One common feature of the environments where Collimonas lives is the presence of fungi, because Collimonas have the ability of not only hydrolyzing the chitin produced by fungi for nutrients, but also producing materials (e.g., P. fluorescens 2-79) to protect themselves from fungal infection. [21] The mutual relationship is common in the oligotrophic environments. Additionally, Collimonas can also obtain electron sources from rocks and minerals by weathering. [21]

In terms of polar areas, such as Antarctic and Arctic region, the soil environment is considered as oligotrophic because the soil is frozen with low biological activities. [19] The most abundant species in the frozen soil are Actinomycetota, Pseudomonadota, Acidobacteriota and Cyanobacteria, together with a small amount of archaea and fungi. [19] Actinomycetota can maintain the activity of their metabolic enzymes and continue their biochemical reactions under a wide range of low temperature. [19] In addition, the DNA repairing machinery in Actinomycetota protects them from lethal DNA mutation at low temperature. [19]

See also

Related Research Articles

<span class="mw-page-title-main">Lake Vostok</span> Antarcticas largest known subglacial lake

Lake Vostok is the largest of Antarctica's almost 400 known subglacial lakes. Lake Vostok is located at the southern Pole of Cold, beneath Russia's Vostok Station under the surface of the central East Antarctic Ice Sheet, which is at 3,488 m (11,444 ft) above mean sea level. The surface of this fresh water lake is approximately 4,000 m (13,100 ft) under the surface of the ice, which places it at approximately 500 m (1,600 ft) below sea level.

<span class="mw-page-title-main">Endolith</span> Organism living inside a rock

An endolith or endolithic is an organism that is able to acquire the necessary resources for growth in the inner part of a rock, mineral, coral, animal shells, or in the pores between mineral grains of a rock. Many are extremophiles, living in places long considered inhospitable to life. The distribution, biomass, and diversity of endolith microorganisms are determined by the physical and chemical properties of the rock substrate, including the mineral composition, permeability, the presence of organic compounds, the structure and distribution of pores, water retention capacity, and the pH. Normally, the endoliths colonize the areas within lithic substrates to withstand intense solar radiation, temperature fluctuations, wind, and desiccation. They are of particular interest to astrobiologists, who theorize that endolithic environments on Mars and other planets constitute potential refugia for extraterrestrial microbial communities.

<span class="mw-page-title-main">Psychrophile</span> Organism capable of growing and reproducing in the cold

Psychrophiles or cryophiles are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from −20 °C (−4 °F) to 20 °C (68 °F). They are found in places that are permanently cold, such as the polar regions and the deep sea. They can be contrasted with thermophiles, which are organisms that thrive at unusually high temperatures, and mesophiles at intermediate temperatures. Psychrophile is Greek for 'cold-loving', from Ancient Greek ψυχρός (psukhrós) 'cold, frozen'.

<span class="mw-page-title-main">Subglacial lake</span> Lake under a glacier

A subglacial lake is a lake that is found under a glacier, typically beneath an ice cap or ice sheet. Subglacial lakes form at the boundary between ice and the underlying bedrock, where gravitational pressure decreases the pressure melting point of ice. Over time, the overlying ice gradually melts at a rate of a few millimeters per year. Meltwater flows from regions of high to low hydraulic pressure under the ice and pools, creating a body of liquid water that can be isolated from the external environment for millions of years.

<span class="mw-page-title-main">Picoplankton</span> Fraction of plankton between 0.2 and 2 μm

Picoplankton is the fraction of plankton composed by cells between 0.2 and 2 μm that can be either prokaryotic and eukaryotic phototrophs and heterotrophs:

Heterotrophic picoplankton is the fraction of plankton composed by cells between 0.2 and 2 μm that do not perform photosynthesis. They form an important component of many biogeochemical cycles.

<span class="mw-page-title-main">Microbial loop</span> Trophic pathway in marine microbial ecosystems

The microbial loop describes a trophic pathway where, in aquatic systems, dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phytoplankton-zooplankton-nekton. In soil systems, the microbial loop refers to soil carbon. The term microbial loop was coined by Farooq Azam, Tom Fenchel et al. in 1983 to include the role played by bacteria in the carbon and nutrient cycles of the marine environment.

<span class="mw-page-title-main">Phosphorus cycle</span> Biogeochemical movement

The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth. The production of phosphine gas occurs in only specialized, local conditions. Therefore, the phosphorus cycle should be viewed from whole Earth system and then specifically focused on the cycle in terrestrial and aquatic systems.

A copiotroph is an organism found in environments rich in nutrients, particularly carbon. They are the opposite to oligotrophs, which survive in much lower carbon concentrations.

<span class="mw-page-title-main">Blood Falls</span> Red-colored seep of saltwater flowing from Taylor Glacier in Antarctica

Blood Falls is an outflow of an iron oxide–tainted plume of saltwater, flowing from the tongue of Taylor Glacier onto the ice-covered surface of West Lake Bonney in the Taylor Valley of the McMurdo Dry Valleys in Victoria Land, East Antarctica.

<span class="mw-page-title-main">Antarctic microorganism</span>

Antarctica is one of the most physically and chemically extreme terrestrial environments to be inhabited by lifeforms. The largest plants are mosses, and the largest animals that do not leave the continent are a few species of insects.

<span class="mw-page-title-main">Wildlife of Antarctica</span> Antarctic wildlife

The wildlife of Antarctica are extremophiles, having adapted to the dryness, low temperatures, and high exposure common in Antarctica. The extreme weather of the interior contrasts to the relatively mild conditions on the Antarctic Peninsula and the subantarctic islands, which have warmer temperatures and more liquid water. Much of the ocean around the mainland is covered by sea ice. The oceans themselves are a more stable environment for life, both in the water column and on the seabed.

<span class="mw-page-title-main">Fungal extracellular enzyme activity</span> Enzymes produced by fungi and secreted outside their cells

Extracellular enzymes or exoenzymes are synthesized inside the cell and then secreted outside the cell, where their function is to break down complex macromolecules into smaller units to be taken up by the cell for growth and assimilation. These enzymes degrade complex organic matter such as cellulose and hemicellulose into simple sugars that enzyme-producing organisms use as a source of carbon, energy, and nutrients. Grouped as hydrolases, lyases, oxidoreductases and transferases, these extracellular enzymes control soil enzyme activity through efficient degradation of biopolymers.

Deinococcus frigens is a species of low temperature and drought-tolerating, UV-resistant bacteria from Antarctica. It is Gram-positive, non-motile and coccoid-shaped. Its type strain is AA-692. Individual Deinococcus frigens range in size from 0.9-2.0 μm and colonies appear orange or pink in color. Liquid-grown cells viewed using phase-contrast light microscopy and transmission electron microscopy on agar-coated slides show that isolated D. frigens appear to produce buds. Comparison of the genomes of Deiococcus radiodurans and D. frigens have predicted that no flagellar assembly exists in D. frigens.

<span class="mw-page-title-main">Phycosphere</span> Microscale mucus region that is rich in organic matter surrounding a phytoplankton cel

The phycosphere is a microscale mucus region that is rich in organic matter surrounding a phytoplankton cell. This area is high in nutrients due to extracellular waste from the phytoplankton cell and it has been suggested that bacteria inhabit this area to feed on these nutrients. This high nutrient environment creates a microbiome and a diverse food web for microbes such as bacteria and protists. It has also been suggested that the bacterial assemblages within the phycosphere are species-specific and can vary depending on different environmental factors.

<span class="mw-page-title-main">Trista Vick-Majors</span> American Antarctic biogeochemist and microbial ecologist

Trista Vick-Majors is an American Assistant Professor in Biological Sciences at Michigan Tech. She is an Antarctic biogeochemist and microbial ecologist, best known for her work showing that microorganisms are present under the Antarctic ice sheet.

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.

<span class="mw-page-title-main">Sea ice microbial communities</span> Groups of microorganisms living within and at the interfaces of sea ice

Sea Ice Microbial Communities (SIMCO) refer to groups of microorganisms living within and at the interfaces of sea ice at the poles. The ice matrix they inhabit has strong vertical gradients of salinity, light, temperature and nutrients. Sea ice chemistry is most influenced by the salinity of the brine which affects the pH and the concentration of dissolved nutrients and gases. The brine formed during the melting sea ice creates pores and channels in the sea ice in which these microbes can live. As a result of these gradients and dynamic conditions, a higher abundance of microbes are found in the lower layer of the ice, although some are found in the middle and upper layers. Despite this extreme variability in environmental conditions, the taxonomical community composition tends to remain consistent throughout the year, until the ice melts.

<span class="mw-page-title-main">Marine food web</span> Marine consumer-resource system

Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers is larger than the biomass of primary producers. This happens because the ocean's primary producers are tiny phytoplankton which grow and reproduce rapidly, so a small mass can have a fast rate of primary production. In contrast, many significant terrestrial primary producers, such as mature forests, grow and reproduce slowly, so a much larger mass is needed to achieve the same rate of primary production.

A sea ice brine pocket is an area of fluid sea water with a high salt concentration trapped in sea ice as it freezes. Due to the nature of their formation, brine pockets are most commonly found in areas below −2 °C (28 °F), where it is sufficiently cold for seawater to freeze and form sea ice. Though the high salinity and low light conditions of brine pockets create a challenging environment for marine mammals, brine pockets serve as a habitat to various microbes. Sampling and studying these pockets requires specialized equipment and alterations to methodologies to accommodate the hyper-saline conditions and subzero temperatures.

References

  1. ↑ ὀλίγος . Liddell, Henry George ; Scott, Robert ; A Greek–English Lexicon at the Perseus Project
  2. ↑ τροφικός . Liddell, Henry George ; Scott, Robert ; A Greek–English Lexicon at the Perseus Project
  3. 1 2 Koch, Arthur L. (July 2001). "Oligotrophs versus copiotrophs". BioEssays. 23 (7): 657–61. doi:10.1002/bies.1091. PMID   11462219. S2CID   39126203.
  4. ↑ Horikoshi, Koki (2016). Extremophiles Where it all Began. Tokyo, Japan: Springer Japan. doi:10.1007/978-4-431-55408-0. ISBN   978-4-431-55407-3. S2CID   199493176.
  5. ↑ Anesio, Alexandre M.; Laybourn-Parry, Johanna (April 2012). "Glaciers and ice sheets as a biome". Trends in Ecology & Evolution. 27 (4): 219–225. doi:10.1016/j.tree.2011.09.012. PMID   22000675.
  6. ↑ Schiermeier, Q. (2011). "Race against time for raiders of the lost lake". Nature . 469 (7330): 275. Bibcode:2011Natur.469..275S. doi: 10.1038/469275a . PMID   21248808.
  7. 1 2 D'Elia, T.; Veerapaneni, R.; Rogers, S. O. (13 June 2008). "Isolation of Microbes from Lake Vostok Accretion Ice". Applied and Environmental Microbiology. 74 (15): 4962–4965. Bibcode:2008ApEnM..74.4962D. doi:10.1128/AEM.02501-07. PMC   2519340 . PMID   18552196.
  8. 1 2 Bulat, Sergey A.; Alekhina, Irina A.; Blot, Michel; Petit, Jean-Robert; de Angelis, Martine; Wagenbach, Dietmar; Lipenkov, Vladimir Ya.; Vasilyeva, Lada P.; Wloch, Dominika M.; Raynaud, Dominique; Lukin, Valery V. (January 2004). "DNA signature of thermophilic bacteria from the aged accretion ice of Lake Vostok, Antarctica: implications for searching for life in extreme icy environments". International Journal of Astrobiology. 3 (1): 1–12. Bibcode:2004IJAsB...3....1B. doi: 10.1017/S1473550404001879 .
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  10. 1 2 Säwström, Christin; Anesio, M. Alexandre; Granéli, Wilhelm; Laybourn-Parry, Johanna (31 October 2006). "Seasonal Viral Loop Dynamics in Two Large Ultraoligotrophic Antarctic Freshwater Lakes". Microbial Ecology. 53 (1): 1–11. doi:10.1007/s00248-006-9146-5. PMID   17075732. S2CID   1833362.
  11. 1 2 Layboum-Parry, Johanna; Marchant, H.J.; Brown, P. (1991). "The plankton of a large oligotrophic freshwater Antarctic lake". Journal of Plankton Research. 13 (6): 1137–1149. doi:10.1093/plankt/13.6.1137. ISSN   0142-7873.
  12. ↑ Henshaw, Tracey; Laybourn-Parry, J. (October 2002). "The annual patterns of photosynthesis in two large, freshwater, ultra-oligotrophic Antarctic lakes". Polar Biology. 25 (10): 744. doi:10.1007/s00300-002-0402-y. ISSN   0722-4060. S2CID   42895583.
  13. ↑ Janzen, D. H. (1974). "Tropical Blackwater Rivers, Animals, and Mast Fruiting by the Dipterocarpaceae". Biotropica. 6 (2): 69–103. doi:10.2307/2989823. JSTOR   2989823.
  14. ↑ Sioli, Harald (1975). "Tropical rivers as expressions of their terrestrial environments" . In Golley, F. B.; Medina, E. (eds.). Tropical Ecological Systems/Trends in Terrestrial and Aquatic Research. New York: Springer. pp.  275–288. ISBN   978-0-387-06706-3.
  15. ↑ German, Laura A. (2004). "Ecological praxis and blackwater ecosystems: a case study from the Brazilian Amazon". Human Ecology. 32 (6): 653–683. doi:10.1007/s10745-004-6831-1. S2CID   153566259.
  16. ↑ Del Valle-Arango, Jorge Ignacio (2003). "Cantidad, calidad y nutrientes reciclados por la hojarasca fina en bosques pantanosos del Pacífico sur colombiano". Interciencia. 28 (8): 443–452.(in Spanish)
  17. ↑ "Study Shows Ocean "Deserts" are Expanding". NOAA. 2008-03-05. Retrieved 2009-07-17.
  18. 1 2 3 4 5 Morita, Richard Yukio (1997). Bacteria in oligotrophic environments: Starvation-survival life style. New York: Chapman & Hall. pp. 50–89. ISBN   9780412106613.
  19. 1 2 3 4 5 6 Makhalanyane, Thulani Peter; Goethem, Marc Warwick Van; Cowan, Don Arthur (2016). "Microbial diversity and functional capacity in polar soils". Current Opinion in Biotechnology. 38: 159–166. doi:10.1016/j.copbio.2016.01.011. hdl:2263/52220. PMID   26921734. S2CID   241167.
  20. 1 2 3 Finn, Damien; Kopittke, Peter M.; Dennis, Paul G.; Dalal, Ram C. (2017). "Microbial energy and matter transformation in agricultural soils" (PDF). Soil Biology and Biochemistry. 111: 176–192. doi:10.1016/j.soilbio.2017.04.010.
  21. 1 2 3 Leveau, Johan H. J.; Uroz, Stéphane; De Boer, Wietse (2010-02-01). "The bacterial genus Collimonas: mycophagy, weathering and other adaptive solutions to life in oligotrophic soil environments". Environmental Microbiology. 12 (2): 281–292. doi:10.1111/j.1462-2920.2009.02010.x. ISSN   1462-2920. PMID   19638176.
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