Copyright © 2020-2021 C.E. by D. Jon Scott
Introduction
Extremophiles, organisms who experience optimum growth in conditions lethal to most others, and extremotolerant organisms who may not necessarily be extremophiles yet can natheless thrive in such conditions, are of extreme interest to astrobiologists.
Note: Currently all of the organisms listed here are prokaryotes. Later this area will be expanded to include eukaryotes.
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Simple Extremophiles
(And Extremotolerant Organisms)
Heat X-Philes: Thermophiles & Hyperthermotolerant, Near-Thermophilic Mesophiles
This group includes not only “simple” thermophiles, with an optimal growth temperature of anywhere from 50°C to 80°C (OGT=65°C±15°C), or 122°F to 176°F (149°F±27°F), but also hyperthermophiles, who have an optimal growth temperature over 80°C (OGT≥80°C) or 176°F (OGT≥176°F).
- Heat X-Philes: Archaea — Thermophilic Archaea & Hyperthermotolerant, Near-Thermophilic Archaeal Mesophiles
- Heat X-Philes: Bacteria — Thermophilic Bacteria & Hyperthermotolerant, Near-Thermophilic Bacterial Mesophiles
Cold X-Philes: Cryophiles & Hyperpsychrotrophic, Near-Cryophilic Mesophiles
Also known as psychrophiles, this group includes organisms with an optimal growth temperature equal to or less than ten degrees celsius (OGT≤10°C).
- Cold X-Philes: Archaea — Cryophilic Archaea & Hyperpsychrotrophic, Near-Cryophilic Archaeal Mesophiles
- Cold X-Philes: Bacteria — Cryophilic Bacteria & Hyperpsychrotrophic, Near-Cryophilic Bacterial Mesophiles
Pressure X-Philes: Barophiles & Hyperbarophilic, Near-Barophilic Mesobarophiles
Also known as piezophiles, this group includes organisms with an optimal growth pressure of 10 Mpa (~100 bar) or higher (≥98.6 atmospheres).
- Pressure X-Philes: Archaea — Barophilic Archaea & Hyperbarotolerant, Near-Barophilic Archaeal Mesobarophiles
- Pressure X-Philes: Bacteria — Barophilic Bacteria & Hyperbarotolerant, Near-Barophilic Bacterial Mesobarophiles
Vacuum X-Philes: Hypobarophiles & Hypobarotolerant, Near-Barophilic Mesobarophiles
- Vacuum X-Philes: Archaea — Hypobarophilic Archaea & Hypobarotolerant, Near-Hypobarophilic Archaeal Mesobarophiles
- Vacuum X-Philes: Bacteria — Hypobarophilic Bacteria & Hypobarotolerant, Near-Hypobarophilic Bacterial Mesobarophiles
Radio X-Philes: Radiophilic & Radioresistant Organisms
Ionizing-radiation-resistant organisms (IRROs) are organisms for whom more than 1,000 Gy (100,000 rd or CGS) are needed
- Radio X-Philes: Archaea — Radiotolerant Archaea & Archaeal Radiophiles
- Radio X-Philes: Bacteria — Radiotolerant Bacteria & Bacterial Radiophiles
Acid X-Philes: Acidophiles & Hyperacidotolerant, Near-Acidophilic Neutriphiles
This group includes organisms capable of thriving in hyperacidic conditions, most of which have an optimal growth pH of 5 or lower (OGpH≤5), although a few have an OGpH slightly above this (e.g., Nanoarchaeum equitans, OGpH=6) but can nonetheless be found flourishing in hyperacidic environments (pH=0.5-1.5).
- Acid X-Philes: Archaea — Acidophilic Archaea & Hyperacidotolerant, Near-Acidophilic Archaeal Neutriphiles
- Acid X-Philes: Bacteria — Acidophilic Bacteria & Hyperacidotolerant, Near-Acidophilic Bacterial Neutriphiles
Base X-Philes: Alkaliphiles & Hyperalkalitolerant, Near-Alkaliphilic Neutriphiles
This group includes organisms with an optimal growth pH of 10 or higher (OGpH≥10)
- Base X-Philes: Archaea — Alkaliphilic Archaea & Hyperalkalitolerant, Near-Alkaliphilic Archaeal Neutriphiles
- Base X-Philes: Bacteria — Alkaliphilic Bacteria & Hyperalkalitolerant, Near-Alkaliphilic Bacterial Neutriphiles
Salt X-Philes: Halophiles & Hyperhalotolerant, Near-Halophilic Organisms
This group includes organisms which require sodium chloride for their growth and reproduction...
- Salt X-Philes: Archaea — Halophilic Archaea
- Salt X-Philes: Bacteria — Halophilic Bacteria
Drouth X-Philes: Xerophiles and Hyperxerotolerant Organisms
This group includes organisms who can thrive and reproduce at water activity lower than that typical for most life on Earth (aw≤0.8)
- Drouth X-Philes: Archaea — Xerophilic Archaea
- Drouth X-Philes: Bacteria — Xerophilic Bacteria
Time X-Philes: Chronotolerant Organisms
This group includes organisms who can survive exceedingly long periods of time; in some cases even the passage of hundreds of millions of years. For example, Virgibacillus marismortui (formerly Bacillus marismortui and Bacillus strain 2-9-3) was revived by scientists from 250-million-year-old spores (Vreeland, 2000); for comparison, the first dinosaurs began appearing about 220 MYA — 30 million years later.
- Time X-Philes: Archaea — Chronotolerant Archaea
- Time X-Philes: Bacteria — Chronotolerant Bacteria
Polyextremophiles
(And Polyextremotolerant Organisms)
Salt & Base X-Philes: Haloalkaliphiles
This group includes polyextremophiles who are simultaneously both halophilic and alkaliphilic.
- Salt & Base X-Philes: Archaea — Haloalkaliphilic Archaea
- Salt & Base X-Philes: Bacteria — Haloalkaliphilic Bacteria
Heat & Acid X-Philes: Thermoacidophiles
This group includes polyextremophiles who are simultaneously both thermophilic and acidophilic.
- Heat & Acid X-Philes: Archaea — Thermoacidophilic Archaea
- Heat & Acid X-Philes: Bacteria — Thermoacidophilic Bacteria
Heat & Pressure X-Philes: Thermobarophiles
This group includes polyextremophiles who are simultaneously both thermophilic and barophilic.
- Heat & Pressure X-Philes: Archaea — Thermobarophilic Archaea
- Heat & Pressure X-Philes: Bacteria — Thermobarophilic Bacteria
Cold & Vacuum X-Philes: Cryohypobarophiles
This group includes polyextremophiles who are simultaneously both cryophilic and hypobarophilic.
- Cold & Vacuum X-Philes: Archaea — Cryohypobarophilic Archaea
- Cold & Vacuum X-Philes: Bacteria — Cryohypobarophilic Bacteria
Cold & Drouth X-Philes: Cryoxerophiles
This group includes polyextremophiles who are simultaneously both cryophilic and xerophilic.
- Cold & Drouth X-Philes: Archaea — Cryoxerophilic Archaea
- Cold & Drouth X-Philes: Bacteria — Cryoxerophilic Bacteria
Sporing X-Philes: Endospore-Forming Bacteria
Bacterial endospores tend to give the bacteria capable of producing them polyextremotolerance. Endospores are known for being able to survive extremely high doses of radiation, vacuum dessication, extreme heat and cold, lack of nutrients, and in some cases even the passage of hundreds of millions of years (for example, Virgibacillus marismortui (formerly Bacillus marismortui and Bacillus strain 2-9-3) was revived by scientists from 250-million-year-old spores (Vreeland, 2000); for comparison, the first dinosaurs began appearing about 220 MYA — 30 million years later).
Master Lists & Themes
Space X-Philes: Astrotolerant Organisms
This group includes polyextremophiles capable of surviving space-like extremes.
- Space X-Philes: Archaea — Astrotolerant Archaea
- Space X-Philes: Bacteria — Astrotolerant Bacteria
Planet X-Philes: Hypergeophilic & Hypergeotolerant Organisms
This group includes polyextremophiles capable of surviving extremes that are planetary in nature, being decidedly unlike conditions found in space.
- Planet X-Philes: Archaea — Hypergeophilic & hypergeotolerant Archaea
- Planet X-Philes: Bacteria — Hypergeophilic & hypergeotolerant Bacteria
