Table 1 Classes of extremophiles with their distinguishing characters and examples
Class
Optimal growth
Examples
Alkaliphile
At or above pH 9
Alkalibacterium psychrotolerans, Bacillus
halodurans, Alkaliphilus transvaalensis
Acidophile
At or below pH 3
Picrophilus oshimae, Acidianus brierleyi,
Ferroplasma acidarmanus
Thermophile
60–80
C
Caldicellulosiruptor saccharolyticus,
Thermoanaerobacter italicus, Thermotoga
neapolitana, Methanogenium frigidum,
Colwellia psychrerythraea
Hyperthermophile Above 80
C
Pyrolobus fumarii, Pyrococcus furiosus,
Geogemma barossii
Psychrophile
At or below 15
C
Desulfotalea psychrophile
Halophile
At or above 0.5 M NaCl
Dunaliella salina, Wallemia ichthyophaga,
Halobacterium salinarum
Xerophile
Capable of growing below
water activity (Wa) of 0.8
Xeromyces bisporus, Trichosporonoides
nigrescens, Artemia salina, Methanosarcina
barkeri
Piezophile
(barophiles)
At or above 50 MPa
(obligate piezophiles)
Thermococcus piezophilus, Shewanella
benthica
Radiophile
Tolerate high levels of
radiation
Deinococcus radiodurans, Thermococcus
gammatolerans
Endolith
Rock-dwelling
Ostracoblabe implexis, Lithopythium
gangliiforme, Desulfovibrio cavernae
Metallophiles
Tolerate high concentration of heavy metals
Ralstonia metallidurans
Fig. 1 Some of the
application areas of
extremophiles
6
G. Mamo and B. Mattiasson