User:Vivientan/sandbox

Original- "Psychrophile"

Psychrophiles or cryophiles (adj. cryophilic) are extremophilic organisms that are capable of growth and reproduction in cold temperatures, ranging from −20 °C to +10 °C.

Many such organisms are bacteria, but psychrophiles also include eukaryotes such as lichens, snow algae, fungi, and wingless midges.

Biology


Psychrophiles are protected from freezing and the expansion of ice by ice-induced desiccation and vitrification (glass transition), as long as they cool slowly. Free living cells desiccate and vitrify with a glass transition between −10 °C and −26 °C. Cells of multicellular organisms may vitrify at temperatures below −50 °C. The cells may continue to have some metabolic activity in the extracellular fluid down to these temperatures, and they remain viable once restored to normal temperatures. Microbial activity has been measured in soils frozen below −39 °C. Among the bacteria that can tolerate extreme cold are Arthrobacter sp., Psychrobacter sp. and members of the genera Halomonas, Pseudomonas, Hyphomonas, and Sphingomonas. Another example is Chryseobacterium greenlandensis, a psychrophile that was found in 120,000-year-old ice.

Some wingless insects (chironomid midges of the genus Diamesa) are still active down to −16 °C. The psychrotrophic pink yeast Rhodotorula glutinis causes food spoilage at temperatures as low as −18 °C. The lichens Umbilicaria antarctica and Xanthoria elegans have been recorded photosynthesizing at temperatures ranging down to −24 °C, and they can grow down to around −10 °C. Higher plants and invertebrates can survive down to around −70 °C but need temperatures of around −2 °C or higher to complete their life cycle.

Temperatures as low as −15 °C are found in pockets of very salty water (brine) surrounded by sea ice. Psychrophiles are true extremophiles because they adapt not only to low temperatures but often also to further environmental constraints. They can be contrasted with thermophiles, which thrive at unusually hot temperatures. In addition to that, distinctions between mesophilic and psychrophilic cold-shock response, including lack of repression of house-keeping protein synthesis and the presence of cold-acclimation proteins (Caps) in psychrophiles, does exist. The environments they inhabit are ubiquitous on Earth, as a large fraction of our planetary surface experiences temperatures lower than 15 °C. They are present in alpine and arctic soils, high-latitude and deep ocean waters, polar ice, glaciers, and snowfields. They are of particular interest to astrobiology, the field dedicated to the formulation of theory about the possibility of extraterrestrial life, and to geomicrobiology, the study of microbes active in geochemical processes. In experimental work at University of Alaska Fairbanks, a 1000-litre biogas digester using psychrophiles harvested from "mud from a frozen lake in Alaska" has produced 200–300 litres of methane per day, about 20–30% of the output from digesters in warmer climates.

Psychrophiles use a wide variety of metabolic pathways, including photosynthesis, chemoautotrophy (also sometimes known as lithotrophy), and heterotrophy, and form robust, diverse communities. Most psychrophiles are bacteria or archaea, and psychrophily is present in widely diverse microbial lineages within those broad groups. Some groups of psychrophilic fungi live in oxygen-poor areas under alpine snowfields. A further group of eukaryotic cold-adapted organisms are snow algae, which can cause watermelon snow. Some multicellular eukaryotes can also be metabolically active at negative temperatures, such as some conifers that can still photosynthesize when it is several degrees under 0 °C (conifers are often more cold-resistant than broadleaf trees). Psychrophiles are interesting enzymes that are very useful models in the research of proteins. Psychrophiles are characterized by lipid cell membranes chemically resistant to the stiffening caused by extreme cold, and often create protein 'antifreezes' to keep their internal space liquid and protect their DNA even in temperatures below water's freezing point. A commonly accepted hypothesis for this cold adaptation is the activity-stability-flexibility relationship, suggesting that psychrophilic enzymes increase the flexibility of their structure to compensate for the 'freezing effect' of cold habitats.

Edits- "Psychrophile"

Psychrophiles or cryophiles (adj. cryophilic) are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from −20 °C to +10 °C. 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 thrive at unusually hot temperatures. Psychrophile is Greek for 'cold-loving'.

Many such organisms are bacteria or archaea, but psychrophiles also include eukaryotes such as lichens, snow algae, fungi, and wingless midges.

Survival
Psychrophiles are protected from freezing and the expansion of ice by ice-induced desiccation and vitrification (glass transition), as long as they cool slowly. Free living cells desiccate and vitrify with a glass transition between −10 °C and −26 °C. Cells of multicellular organisms may vitrify at temperatures below −50 °C. The cells may continue to have some metabolic activity in the extracellular fluid down to these temperatures, and they remain viable once restored to normal temperatures.

Preventing the stiffening of the lipid cell membrane is key, as this is important for the survival and functionality of these microorganisms. To accomplish this, psychrophiles adapt lipid membrane structures that have a high content of unsaturated fatty acids that are short. Compared to longer saturated fatty acids, incorporating this type of fatty acid allows for the lipid cell membrane to have a lower melting point. In addition, carotenoids are present in the membrane, which help modulate the fluidity of it.

Psychrophiles also create antifreeze proteins to keep their internal space liquid and protect their DNA even in temperatures below water's freezing point, by supercooling the interior fluid. These proteins allow for the microorganism to tolerate freezing conditions, instead of what was originally thought of, which was allowing the microorganism to avoid freezing conditions. A commonly accepted hypothesis for this cold adaptation is the activity-stability-flexibility relationship, suggesting that psychrophilic enzymes increase the flexibility of their structure to compensate for the 'freezing effect' of cold habitats.

Diversity
Psychrophiles use a wide variety of metabolic pathways, including photosynthesis, chemoautotrophy (also sometimes known as lithotrophy), and heterotrophy, and form robust, diverse communities. Most psychrophiles are bacteria or archaea, and psychrophily is present in widely diverse microbial lineages within those broad groups. Some groups of psychrophilic fungi live in oxygen-poor areas under alpine snowfields. A further group of eukaryotic cold-adapted organisms are snow algae, which can cause watermelon snow. Some multicellular eukaryotes can also be metabolically active at negative temperatures, such as some conifers that can still photosynthesize when it is several degrees under 0 °C (conifers are often more cold-resistant than broadleaf trees).

Habitat
The environments they inhabit are ubiquitous on Earth, as a large fraction of our planetary surface experiences temperatures lower than 15 °C. They are present in alpine and arctic soils, high-latitude and deep ocean waters, polar ice, glaciers, and snowfields. Microbial activity has been measured in soils frozen below −39 °C. In addition to their temperature limit, psychrophiles must also be able to adapt to other extreme environmental constraint that may arise, as a result of their habitat. These other environmental constraints include high pressure in the deep sea, and high salt concentration on some sea ice, all of which must be overcome.

Examples
Among the bacteria that can tolerate extreme cold are Arthrobacter sp., Psychrobacter sp. and members of the genera Halomonas, Pseudomonas, Hyphomonas, and Sphingomonas. Another example is Chryseobacterium greenlandensis, a psychrophile that was found in 120,000-year-old ice.

Some wingless insects (chironomid midges of the genus Diamesa) are still active down to −16 °C. The psychrotrophic pink yeast Rhodotorula glutinis causes food spoilage at temperatures as low as −18 °C. The lichens Umbilicaria antarctica and Xanthoria elegans have been recorded photosynthesizing at temperatures ranging down to −24 °C, and they can grow down to around −10 °C. Higher plants and invertebrates can survive down to around −70 °C but need temperatures of around −2 °C or higher to complete their life cycle.

Assignment 5 (final)
Psychrophiles or cryophiles (adj. psychrophilic or cryophilic) are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from −20 °C to +10 °C. 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. Psychrophile is Greek for 'cold-loving'.

Many such organisms are bacteria or archaea, but some eukaryotes such as lichens, snow algae, fungi, and wingless midges, are also classified as psychrophiles.

Habitat
The environments psychrophiles inhabit are ubiquitous on Earth, as a large fraction of our planetary surface experiences temperatures lower than 15 °C. They are present in permafrost, polar ice, glaciers, snowfields and deep ocean waters. These organisms can also be found in pockets of sea ice with high salinity content. Microbial activity has been measured in soils frozen below −39 °C. In addition to their temperature limit, psychrophiles must also adapt to other extreme environmental constraint that may arise, as a result of their habitat. These constraints include high pressure in the deep sea, and high salt concentration on some sea ice.

Survival
Psychrophiles are protected from freezing and the expansion of ice by ice-induced desiccation and vitrification (glass transition), as long as they cool slowly. Free living cells desiccate and vitrify between −10 °C and −26 °C. Cells of multicellular organisms may vitrify at temperatures below −50 °C. The cells may continue to have some metabolic activity in the extracellular fluid down to these temperatures, and they remain viable once restored to normal temperatures.

They must also overcome the stiffening of their lipid cell membrane, as this is important for the survival and functionality of these organisms. To accomplish this, psychrophiles adapt lipid membrane structures that have a high content of short, unsaturated fatty acids. Compared to longer saturated fatty acids, incorporating this type of fatty acid allows for the lipid cell membrane to have a lower melting point, which increases the fluidity of the membranes. In addition, carotenoids are present in the membrane, which help modulate the fluidity of it.

Antifreeze proteins are also synthesized to keep psychrophiles' internal space liquid, and to protect their DNA when temperatures drop below water's freezing point. By doing so, the protein prevents any ice formation or recrystallization process from occurring.

The enzymes of these organisms have been hypothesized to engage in a activity-stability-flexibility relationship as a method for adapting to the cold; the flexibility of their enzyme structure will increase as a way to compensate for the freezing effect of their environment.

Examples
Among the bacteria that can tolerate extreme cold are Arthrobacter sp., Psychrobacter sp. and members of the genera Halomonas, Pseudomonas, Hyphomonas, and Sphingomonas. Another example is Chryseobacterium greenlandensis, a psychrophile that was found in 120,000-year-old ice.

Umbilicaria antarctica and Xanthoria elegans are lichens that have been recorded photosynthesizing at temperatures ranging down to −24 °C, and they can grow down to around −10 °C. Some multicellular eukaryotes can also be metabolically active at sub-zero temperatures, such as some conifers; those in the Chironomidae family are still active at −16 °C.

Penicillium is a genus of fungi that is also psychrophilic.