An extremophile (from Latin extremus meaning “extreme” and Greek philia meaning “love” ).
Extremophiles are living organisms with the ability to survive and thrive in extreme environments as a result of different physiological and molecular adaptations.
These organisms thrive in extreme niches, ice, and salt solutions, as well as acid and alkaline conditions.
Some might grow in toxic waste, organic solvents, heavy metals, or in several other habitats that are considered inhospitable for life.
Most extremophiles are prokaryotic organisms with few eukaryotes.
These extremophiles are defined by the environmental conditions in which they can survive and thrive optimally.
Applications of Extremophiles
- Exremophilic enzymes have been model systems to study enzyme evolution, enzyme stability, activity, mechanism, protein structure, function, and biocatalyst under extreme conditions.
- Enzymes from these organisms such as amylase, protease, cellulases and lipases are used on an industrial scale.
- Extroenzymes like Taq polymerase from Thermus aquaticus is an ideal for use in a polymerase chain reaction as it reduces the need for adding extra polymerase during the reaction.
- Enzymes from extremophiles can also be used in bioremediation processes like toxifying wastewater and air and removing metallic waste from sewages and industries.
Types of Extremophiles
Extremophiles can be divided into two categories,
- Extremophilic organisms that require one or more extreme conditions to survive.
- Extremotolerant organisms which can tolerate extreme conditions of one or more physical parameters even though they grow optimally at neutral conditions.
- Extremophiles include members of all three domains of life; bacteria, archaea, and eukarya.
These are classified according to the conditions in which they grow –
Thermophiles – Organisms growing at high temperature.
Hyperthermophiles – Organisms growing at very high temperature.
Psychrophiles – Organisms that grow at low temperature.
Acidophiles – Organisms thriving in habitats with acidic PH.
Alkaliphiles – Organisms thriving in habitats with basic PH.
Halophiles – Organisms that grow well in an environment with NaCl.
Radoduric – Organisms that grow well in the presence of high radiation.
Barophiles – Organisms that grow best under pressure.
|Thermophiles||Submarine hydrothermal vents||80°C to 115°C|
|Hyperthermophiles||Deep-sea||110 °C to 121 °C|
|Psychrophiles||Ice||-20 °C to -25 °C|
|Acidophiles||Volcanic springs, acid mine drainage||pH -0.06 to 1.0|
|Alkaliphiles||Soda lakes||pH > 11|
|Halophiles||NaCl||>5 M NaCl|
|Radoduric||Cosmic rays, X-rays, radioactive decay||1,500 to 6,000 Gy|
|Barophiles||Mariana Trench||1,100 bar|
- Psychrophiles are nothing but cold-loving organisms.
- It is an organism that adapts to low temperature growth.
- Maximum growth temperature above 15°C and maximum growth temperature above 20°C and minimum 0°C.
- Thermophiles (literally heat lovers) are organisms that grow above temperatures (25-40 ° C) that sustain most life forms.
- In general, thermophiles show a maximum growth rate at temperatures above 45°C.
- Thermophiles are a group of heat-loving microorganisms, usually above 45°C.
- They are depleted of various ecological structures such as deep ocean hydrothermal vents, terrestrial hot springs and other extreme geological/geological sites including volcanic sites, decaying tectonically active defects as well as compost and organic deep organic landfills.
- Morrison and Tanner (1922) provoked cultures of aerobic thermophilic bacteria from water samples from the Illinois State Water Survey.
- Hyperthromophils are organisms that can withstand extremely high temperatures (above 80 ° C) and grow.
- Hypothermophiles are a type of thermophiles that can withstand even higher temperatures than other thermophiles.
- The maximum temperature of growth for hyperthermophiles is 80 ° C, but it can withstand temperatures above 100 ° C.
- Hyperthermophilic isolated from hot springs in Yellowstone National Park were first reported in 1965 by Thomas de Brick. Since then, more than 70 species have been established.
Most are able to cope with other extreme conditions such as hyperthermophiles, high pH and high pressure.
- Most hyper thrombophilic organisms are found in hot springs and boiling steam vents where even moderate thermophiles cannot survive or thrive.
- Hyperthermophilic are mostly related to the archaea group in which very few species are species of bacteria.
- The cell membrane contains high amounts of saturated fatty acids to maintain its shape at high temperatures.
- The most extreme hyperthermophiles reside on the heated walls of deep ocean hydrothermal vents, which require a temperature of at least 90 ° C to survive.
- Some of the common examples of hyperthermophilic organisms are Thermoproteus uzoniensis, Staphylothermus marinus, Pyrodictium abyssi, Pyrococcus furiosus, Hypothermus butylicus, Pryococcus woesei, Pyrodictium brockii, Pyrodictium occultum, etc.
- Acidophilus is an organism that can survive and thrive in highly acidic conditions (usually at pH 2.0).
- Acidophilic microorganisms thrive in very low pH natural and man-made environments such as acidic lakes, some hydrothermal systems, acid sulfate soils, sulfide regoliths and ores as well as metal and coal mine-affected environments.
- The high acidic atmosphere is formed by the id oxidation of metals and other sulfidic minerals formed by a series of acidophilic and acid-tolerant prokaryotic and eukaryotic life forms.
- Heterotrophic, acidophilic bacteria, often living in close proximity to chamolithotrophic primary producers, but also isolated from highly acidic environments.
- The most widely studied acidophils are prokaryotes that oxidize reduced iron and sulfur.
- They can produce oxidative dissolutions such as metal sulfide minerals such as pyrite (Phase 2), from which they rapidly acidify the environment (often with a pH less than 3) in which they thrive.
- Natural acidic environments including volcanic areas, hydrothermal sources, deep ocean vents, metal mining areas and animal stomachs.
- Archea represents the largest acidophilic group of organisms. Physically, acidophils are very diverse: aerobic and flexible anaerobic, chamolithotrophs and a variety of heterotrophic prokaryotes, phototrophic eukaryotes, predatory protozoa and others.
- Some examples of acidophilic organisms include – Lactobacillus, Thiobacillus, Sulfolobus, Bacillus acidocaldarius, Thermoplasma acidophilus, Picrophilus, Ferroplasma acidiphilum, Acidithiobacillus Leptospirillum, Acidobacterium spp., Sulfobacillus, etc.
- Alkaliphiles are a group of extreme files that can live and thrive in environments with extremely high pH values (9-13), while the best pH is 10.
- There are two types of alkalophilic organisms; Mandatory alkaloids grown only in pH environments above 9 and fatty alkaloids that can live in both neutral pH and alkaline conditions.
- Mostly those eubacteria and some archaebacteria prokaryotes.
- Alkalophiles are thought to be the oldest forms of life on Earth that originated billions of years ago in the alkaline hydrothermal vent systems of the ocean.
- Alkalophiles thrive in many geographical locations on Earth, in natural and man-made alkaline environments such as alkaline soda lakes, soda deserts and saline soda soils.
- Other natural habitats in which alkalophiles thrive include alkaline serpentine ponds, marine bodies, and alkaline hydrothermal vents.
- Some of the examples of alkaliphiles include – Bacillus alkaliphilus, Bacillus pasteurri, Bacillus halodurans, Halobacterium, Clostridium paradoxum, Halomonas pantelleriensis, Alkaliphilus hydrothermalis, etc.
- Halophiles are of two types; obligate halophiles that require a NaCl concentration of 3% or more and halotolerant that survive at both average salt concentrations and higher.
- Halophiles are a group of extremophiles that require high salt concentrations for their survival and growth.
- The general features of halophilic microorganisms are low nutritional requirements and resistance to high concentrations of salt with the capacity to balance the osmotic pressure of the environment.
- The salt requirement in halophiles is classified into three groups; low (1-3%), moderate (3-15%), and extreme (15-30%). Inhabit different ecosystems characterized by a salinity higher than seawater that range from hypersaline soils, springs, salt lakes, sabkhas to marine sediments.
- These organisms are found in all three domains of life, i.e., Archaea, Bacteria, and Eukaryota.Halophilic bacteria are more abundant in specific phylogenetic subgroups, most of which belong to Halomonadaceae, a family of Proteobacteria.
Halophiles are of two types –
- Obligate halophiles – that require NaCl concentration of 3% or more
- Halotolerant – that survive at both average salt concentrations and higher.
Some common examples of halophilic organisms in terms of their salt requirement are,
- Slightly halophilic – Erwinia, Bacillus hunanensis, Halomonas zhaodongensis, Alkalibacterium thalassium, etc.
- Moderately halophilic – Spiribacter salinus, Halobacillus sediminis, Halobacillus saliçampi, Marinobacter piscensis, Idiomarina aquatica, etc.
- Extreme halophilic – Halococcus salifodinae, Halobacterium salinarum, Limimonas halophilia, Lentibacillus kimchii, Sporohalobacter salinus, etc.
- Metallotolerant microorganisms are microorganisms that are capable of tolerating and detoxifying high levels of dissolved heavy metals.
- Most metallotolerant microorganisms tend to be acidophilic as the physiological activities of such microorganisms enable tolerance against high metal concentrations.
- As many metals are more soluble at acidic pH, acidophiles are typically exposed to high metal concentrations and can survive in 1000-fold higher amounts than neutrophilic microorganisms.
- Metallotolerant microbes belong to all bacterial groups studied, mostly among aerobic and facultative aerobic chemo-heterotrophic microorganisms. Polluted soils and waters with untreated industrial and urban wastes and samples of the natural environment with a high concentration of metals are important habitats of metallotolerant microorganisms.
- Some of the common examples of metallotolerant species include – Bacillus subtilis, Bacillus megaterium, Acidithiobacillus ferrooxidans, Acidithiobacillus caldus, Corynebacterium diptheriae, Acidiphilium rubrum, Acidiphilium multivorum, etc.
- Radiophiles are a group of extremophiles that are capable of surviving extreme forms of radiation like ionizing radiation (gamma rays) and UV radiation.
- Studies on radiophiles are quite limited as they are to be isolated from extreme environments like outer space of other planets.