Copyright © 2020-2021 C.E. by D. Jon Scott
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.
Permissions for Use
Permission is hereby granted to show and distribute this material for educational purposes with proper attribution.
Even where fair use does not necessitate the use of proper attribution, it would be appreciated, as this project required an enormous amount of work.
Extremophiles & Extremotolerant Organisms
By Type of Extremophily and/or Extremotolerance
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
(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 & Pressure X-Philes: Cryobarophiles
This group includes polyextremophiles who are simultaneously both cryophilic and barophilic.
- Cold & Pressure X-Philes: Archaea — Cryobarophilic Archaea
- Cold & Pressure X-Philes: Bacteria — Cryobarophilic 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
Cold & Radio X-Philes: Radiocryophiles
This group includes polyextremotolerant who are simultaneously both cryophilic (or at least cryotrophic) and radiotolerant.
- Cold & Radio X-Philes: Archaea — Radiocryophilic Archaea
- Cold & Radio X-Philes: Bacteria — Radiocryophilic Bacteria
Heat & Radio X-Philes: Radiothermophiles
This group includes polyextremotolerant who are simultaneously both thermophilic (or at least cryotrophic) and radiotolerant.
- Heat & Radio X-Philes: Archaea — Radiothermophilic Archaea
- Heat & Radio X-Philes: Bacteria — Radiothermophilic 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
X-Philes: Master List
Master list of all extremotolerant prokaryotes.
- Taxonomic tree of extremophilic and extremotolerant prokaryotes
- Table of extremophilic and extremotolerant prokaryotes
- X-Philes: Archaea — Extremotolerant Archaea
- Taxonomic tree of extremophilic and extremotolerant archaea
- Alphabetic table of extremophilic and extremotolerant archaea
- X-Philes: Bacteria — Extremotolerant Bacteria
Space X-Philes: Astrotolerant Organisms
This group includes polyextremophiles capable of surviving space-like extremes.
- Taxonomic tree of astrotolerant prokaryotes
- Alphabetical table of astrotolerant prokaryotes
- Space X-Philes: Archaea — Astrotolerant Archaea
- Taxonomic tree of astrotolerant archaea
- Table of astrotolerant archaea
- Space X-Philes: Bacteria — Astrotolerant Bacteria
- Taxonomic tree of astrotolerant bacteria
- Table of 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.
- Taxonomic tree of hypergeophilic and hypergeotolerant prokaryotes
- Alphabetic table of hypergeophilic and hypergeotolerant prokaryotes
- Planet X-Philes: Archaea — Hypergeophilic & hypergeotolerant Archaea
- Taxonomic tree of hypergeophilic and hypergeotolerant archaea
- Alphabetic table of hypergeophilic and hypergeotolerant archaea
- Planet X-Philes: Bacteria — Hypergeophilic & hypergeotolerant Bacteria
- Taxonomic tree of hypergeophilic and hypergeotolerant bacteria
- Table of hypergeophilic and hypergeotolerant bacteria
Numbers Overview #1
Instances of extremophily/extremotolerance
|Extremophily/extremotolerance type||Prokaryotic subgroups||Prokarya total|
|Total instances of hypergeophily||535||148||683|
|Total instances of hypergeotolerance||535||465||1000|
|Total instances of astrotolerance (excluding hyperthermophily)||214||2240||2454|
|Total instances of astrotolerance (including hyperthermophily)||214||2557||2771|
|Total instances of extremophily||749||2388||3137|
|Total instances of extremotolerance||749||2705||3454|
Note #1: “Instances of hypergeophily” and “instances of hypergeotolerance” currently differ only in that the former includes instances of true thermophily but not hyperthermotolerance, while the latter includes instances of hyperthermotolerance.
Note #2: “Total instances of extremotolerance” was calculated here hastily as hypergeotolerance plus astrotolerance.
Numbers Overview #2
Extremophiles & extremotolerant prokaryotes
|Extremophily/extremotolerance type||Prokaryotic subgroups||Prokarya total|
|Total extremophilic/extremotolerant prokaryotes||349||788||1137|