Journal of Biotechnology 64 (1998) 39 – 52
Review article
Hyperthermophiles and their possible potential in biotechnology
Harald Huber *, Karl O. Stetter
Lehrstuhl für Mikrobiologie und Archaeenzentrum, Uni6ersität Regensburg, 93053 Regensburg, Germany
Received 19 January 1998; accepted 9 April 1998
Abstract
To develop novel processes in microbial biotechnology organisms with outstanding properties are required.
Archaea represent a nearly unexplored third domain (‘continent’) of life, which harbours organisms living in extreme
environments such as alkaline to acidic hot springs, anaerobic sediments and highly saline environments. From high
temperature terrestrial and marine biotopes many extreme heat-loving (hyperthermophilic) Archaea and Bacteria have
been isolated, which grow at temperatures between 80 and 113°C. Within the 16S rRNA-based phylogenetic tree of
life, hyperthermophiles occupy the deepest phylogenetic branches representing more than 30 genera. In their mode to
gain energy, they exhibit a great variety: obligate chemolithoautotrophs utilizing only CO2, hydrogen, and different
sulfur compounds are primary producers in hot and anaerobic environments. Organotrophs grow on organic acids,
alcohols, sugars, amino acids, or polymers like starch or chitin. This diversity in combination with their unusual heat
resistance makes hyperthermophiles appropriate for new biotechnological applications at high temperatures. After
cloning the genes into easy cultivable mesophiles, enzymes active at temperatures up to 130°C are produced for food
industry, biochemical and molecular research, or chemical industry. In addition, cultures can be applied directly in
chemical processes like desulfurication of flue gases and in biohydrometallurgical processes. © 1998 Elsevier Science
B.V. All rights reserved.
Keywords: Archaea; Hyperthermophilic; Phylogeny; Biotechnology; Volcanism
1. Introduction
* Corresponding author. Tel.: + 49 941 9433185; fax: + 49
941 9432403; e-mail: [email protected]
Hyperthermophilic Bacteria and Archaea (former: archaebacteria) represent the organisms at
the upper temperature border of life (Stetter and
Zillig, 1985; Brock, 1986; Stetter, 1992). Hyper-
0168-1656/98/$ - see front matter © 1998 Elsevier Science B.V. All rights reserved.
PII S0168-1656(98)00102-3
40
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
thermophiles belong to phylogenetically distant
groups and may represent rather ancient adaptations to heat. As a rule, they grow fastest (optimally) between 80 and 110°C. In contrast to usual
thermophiles, hyperthermophiles are unable to
grow below 60°C. The most extreme hyperthermophile, Pyrolobus fumarii is so well adapted to
high temperatures that it does not even grow at
85°C or below (Blöchl et al., 1997). Due to their
heat adaptation there is an increasing interest for
applications in biotechnological processes.
Metallosphaera sedula survive for several months
(Table 1), a requirement to be successfully transported world-wide through the stratosphere. To
cultivate hyperthermophiles, aerobic and anaerobic
samples are taken from hot water, sediments and
rocks. In the laboratory, aerobic and anaerobic
enrichment cultures on various substrates are prepared at conditions corresponding to the original
environment. Hyperthermophilic enrichment cultures can be purified by direct cloning of single cells
by using ‘optical tweezers’ (Huber et al., 1995b).
2. Environments and enrichment of
hyperthermophiles
3. Phylogeny of hyperthermophiles
Hyperthermophiles have been isolated almost
exclusively from environments with in situ temperatures between about 80 and 115°C. Natural
biotopes of hyperthermophiles on land are watercontaining volcanic areas like solfataric fields and
hot springs, with low salinity and a wide range of
pH values (around pH 0.5 – 8.5). Marine biotopes
are shallow submarine hydrothermal systems,
abyssal hot vents (‘Black Smokers’), and active
seamounts (Huber et al., 1990a). These environments contain high concentrations of salt (around
3%) and the pHs are slightly acidic to slightly
alkaline (pH 5–8.5). In addition, smouldering coal
refuse piles and geothermal power plants are manmade further biotopes for hyperthermophiles
(Marsh and Norris, 1985; Fuchs et al., 1995).
Communities of hyperthermophiles have also been
discovered within oil-bearing deep geothermally
heated soils (Stetter et al., 1993). Due to the low
solubility of oxygen at high temperatures and the
presence of reducing gasses, biotopes of hyperthermophiles are mainly anoxic. However, air-exposed
surfaces of solfataric fields may contain reasonable
amounts of oxygen. Although unable to grow,
hyperthermophiles may survive for long times at
ambient temperature. This ability may be essential
for dissemination through the cold atmosphere and
hydrosphere. In agreement, viable hyperthermophiles could be isolated from cold Beaufort Sea
water and Pacific water neighbouring active Macdonald Sea Mount (Huber et al., 1990a; Stetter et
al., 1993). In the laboratory, air-dried cultures of
The 16S rRNA-based universal phylogenetic tree
shows a tripartite division of the living world
consisting of the domains Bacteria, Archaea and
Eucarya (Woese and Fox, 1977; Woese et al., 1990;
Fig. 1). The root is derived from phylogenetic trees
of duplicated genes of ATPase subunits and elongation factors Tu and G (Iwabe et al., 1989). Short
phylogenetic branches indicate a rather slow clock
of evolution. Deep branching points are evidence
for early separation of two groups. For example,
the separation of the Bacteria from the Eucarya–
Archaea lineage (Fig. 1) is the deepest and earliest
branching point known so far. The Archaea consist
of two major kingdoms: The Crenarchaeota (Sulfolobales – Thermoproteales – ‘Desulfurococcales’)
and the Euryarchaeota (Extreme Halophiles–
Methanogens). Recently evidence was found for
the existence of a third kingdom tentatively named
Korarchaeota (Barns et al., 1994; Burggraf et al.,
1997b).
Table 1
Survival of air-dried cultures of M. sedula grown on sulfidic ores
Storage time
Room temperature
−20°C
−70°C
1
2
1
4
+
+
−
−
+
+
+
+
+
+
+
n.d.
week
weeks
month
month
Cultures (about 107 cells) were air-dried on nitrocellulose
filters and stored at the indicated temperatures. Survival was
tested by inoculation of fresh media (Huber et al., 1989a) with
the filters after the listed periods of time.
n.d., not determined.
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
41
Fig. 1. Hyperthermophiles within the phylogenetic tree; schematically redrawn and modified from Woese et al. (1990).
Surprisingly, all the deepest and shortest lineages within the universal phylogenetic tree are
represented by hyperthermophiles, including
Aquifex and Thermotoga within the Bacteria; Pyrodictium, Pyrolobus, Pyrobaculum, Desulfurococcus, Sulfolobus, Methanopyrus, Thermococcus,
Methanothermus, Archaeoglobus within the Archaea (Fig. 1, bold lines). Based on these observations, hyperthermophiles appear to be the most
primitive organisms still existing and the last com-
mon ancestor may have been a hyperthermophile
(Stetter, 1994).
4. Taxonomy of hyperthermophiles
So far, around 65 species of hyperthermophilic
Bacteria and Archaea are known (Table 2). They
are divergent by their phylogeny and physiological properties. After a recent reclassification, they
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
42
Table 2
Taxonomy and upper growth temperatures of hyperthermophiles
Order
Genus
Species
Bacteria
Thermotogales
Thermotoga
T.
T.
T.
T.
T.
F.
F.
Archaea
Sulfolobales
90
90
84
72a
77a
80a
80a
(Huber et al., 1986)
(Jannasch et al., 1988)
(Windberger et al., 1989)
(Ravot et al., 1995)
(Huber et al., 1989c)
(Patel et al., 1985)
(Huber et al., 1990b)
Aquifex
A. pyrophilus
‘‘A. aeolicus’’ G!
95
93
(Huber et al., 1992)
Sulfolobus
S. acidocaldarius
S. solfataricus G!
S. shibatae
S. metallicus
M. sedula
M. prunae
A. infernus
A. brierleyi
A. ambi6alens
S. azoricus
85
87
86
75a
80a
80a
95
75a
95
89
(Brock et al., 1972)
(Zillig et al., 1980)
(Grogan et al., 1990)
(Huber and Stetter, 1991)
(Huber et al., 1989a)
(Fuchs et al., 1995)
(Segerer et al., 1986)
(Brierley and Brierley, 1973)
(Zillig et al., 1987a; Fuchs et al., 1996)
(Segerer et al., 1991)
Metallosphaera
Acidianus
Stygiolobus
Thermoproteales
Reference
maritima G!
neapolitana
thermarum
elfii
africanus
nodosum
islandicum
Thermosipho
Fer6idobacterium
Aquificiales
Tmax (°C)
Thermoproteus
Pyrobaculum
Thermofilum
‘‘Desulfurococcales’ Desulfurococcus
’
Staphylothermus
Sulfophobococcus
Stetteria
Aeropyrum
‘‘Igneococcus’’
Thermosphaera
‘‘Thermodiscus’’
Pyrodictium
Hyperthermus
Pyrolobus
T. tenax
T. neutrophilus
T. uzoniensis
P. islandicum
P. organotrophum
P. aerophilum G!
T. pendens
T. librum
D. mobilis
97
97
97
103
103
104
95
95
95
(Zillig et al., 1981)
(Stetter, 1986)
(Bonch-Osmolovskaya et al., 1990)
(Huber et al., 1987)
(Huber et al., 1987)
(Völkl et al., 1993)
(Zillig et al., 1983a)
(Stetter, 1986)
(Zillig et al., 1982)
D. mucosus
‘‘D. saccharo6orans’’
D. amylolyticus
S. marinus
S. zilligii
S. hydrogenophila
A. pernix
‘‘I. islandicus’’
T. aggregans
‘‘T. maritimus’’
P. occultum
P. brockii
P. abyssi
H. butylicus
P. fumarii G!
97
97
97
98
95
102
100
103
90
98
110
110
110
108
113
(Zillig et al., 1982)
(Stetter, 1986)
(Bonch-Osmolovskaya et al., 1985)
(Fiala et al., 1986)
(Hensel et al., 1997)
(Jochimsen et al., 1997)
(Sako et al., 1996)
(Burggraf et al., 1997a)
(Huber et al., 1998)
(Stetter, 1986)
(Stetter et al., 1983)
(Stetter et al., 1983)
(Pley et al., 1991)
(Zillig et al., 1990)
(Blöchl et al., 1997)
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
43
Table 2 (continued)
Order
Thermococcales
Genus
Species
Tmax (°C)
Reference
Thermococcus
T.
T.
T.
T.
T.
T.
T.
T.
P.
P.
P.
93
98
98
90
90
93
103
100
103
103
102
(Zillig et al., 1983b)
(Neuner et al., 1990)
(Miroshnichenko et al., 1989)
(Kobayashi et al., 1994)
(Keller et al., 1995)
(Huber et al., 1995a)
(Godfroy et al., 1996)
(González et al., 1995)
(Fiala and Stetter, 1986)
(Zillig et al., 1987b)
(Erauso et al., 1993)
Pyrococcus
celer
litoralis
stetteri
profundus
alcaliphilus
chitonophagus
fumicolans
peptonophilus
furiosus G!
woesei
abyssi
A. fulgidus G!
A. profundus
A. 6eneficus
F. placidus
92
92
88
95
(Stetter, 1988)
(Burggraf et al., 1990a)
(Huber et al., 1997)
(Hafenbradl et al., 1996)
Methanobacteriales Methanothermus
M. fer6idus
M. sociabilis
97
97
(Stetter et al., 1981)
(Lauerer et al., 1986)
Methanococcales
Methanococcus
M. thermolithotrophicus
M. jannaschii G!
M. igneus
70a
86
91
(Huber et al., 1982)
(Jones et al., 1983)
(Burggraf et al., 1990b)
Methanopyrales
Methanopyrus
M. kandleri
Archaeoglobales
Archaeoglobus
Ferroglobus
110
(Kurr et al., 1991)
G!, Genom sequenced or under sequencing.
a
Moderate thermophiles related to hyperthermophiles.
are grouped into 29 genera and ten orders (Table
2; Fuchs et al., 1996; Burggraf et al., 1997a).
Within the Bacteria, Aquifex pyrophilus and Thermotoga maritima exhibit the highest growth temperatures with 95 and 90°C, respectively (Table
2). Within the Archaea, the organisms with the
highest growth temperatures (between 103 and
113°C) are members of the genera Pyrolobus,
Pyrobaculum, Pyrodictium, Pyrococcus and
Methanopyrus (Table 2).
5. Physiological properties of hyperthermophiles
Hyperthermophiles are well adapted to their
biotopes, being able to grow at high temperatures
and extremes of pH, redox potential and salinity
(Tables 2 and 4). Within their habitats, they form
complex ecosystems consisting of a variety of
primary producers and decomposers of organic
matter. Primary producers are chemolithoau-
totrophs using inorganic electron donors and acceptors in their energy-yielding reactions (Table
3).
5.1. Extreme acidophiles
In terrestrial and marine solfataric fields and in
smouldering coal refuse piles extremely
acidophilic hyperthermophiles representing the
genera Sulfolobus, Metallosphaera (Fig. 2d), Acidianus and Stygiolobus are found (Brock, 1978,
1986; Stetter, 1992; Fuchs et al., 1995). They are
cocoid- to lobed-shaped and grow aerobically,
facultatively aerobically or strictly anaerobically
at acidic pH (optimum between pH 2 and 3; Table
4). Members of the genus Sulfolobus are strict
aerobes growing autotrophically by oxidation of
S0, S2 − or H2, forming sulfuric acid or water as
an end-product (Tables 3 and 4). Furthermore
ferric iron and molybdate can be reduced under
microaerobic conditions (Brierley and Brierley,
44
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
1982). In addition, Sulfolobus metallicus is able to
grow by leaching of sulfidic ores (Huber and
Stetter, 1991). Several Sulfolobus isolates are facultative or obligate heterotrophs, using sugars,
yeast extract and peptone as substrates (Brock,
1978). This includes the type strains of Sulfolobus
acidocaldarius and Sulfolobus solfataricus, which
are in contrast to their original description, unable to grow lithoautotrophically now (Huber et
al., 1989a). All Sulfolobus strains grow at low
ionic strength and in agreement with this, Sulfolobus was so far not isolated from marine solfataric fields. Both Metallosphaera species, which
differ from the Sulfolobus strains by a 7% higher
GC-content of their DNA (Table 4), are powerful
oxidizers of sulfidic ores like pyrite, chalcopyrite
and sphalerite, forming sulfuric acid and solubilizing heavy metal ions (Table 3). Members of the
genus Acidianus, similar to the Sulfolobus species,
Table 3
Energy-yielding reactions in chemolithoautotrophic hyperthermophiles
Energy-yielding reaction
Genera
4H2+CO2 “ CH4+2H2O
Methanopyrus,
Methanothermus,
Methanococcus
H2+S0 “ H2S
Pyrodictium, Thermoproteus,
Pyrobaculum, Acidianus,
Stygiolobus
4H2+H2SO4 “ H2S+4H2O Archaeoglobus
3H2+H2SO3 “ H2S+3H2O Archaeoglobus
5H2+S2O2−
Pyrolobus, Archaeoglobus,
3
Ferroglobus
“2H2S+3H2O
H2+HNO3 “ HNO2+H2O Pyrobaculum, Aquifex
4
Pyrolobus
H2+H++NO−
3
−
“NH+
4 +OH +2 H2O
H2+1/2 O2 “H2O
2S0+3O2+2H2O “H2SO4
(2FeS2+7O2+2H2O
“2FeSO4+2H2SO4)
NO−
3 +2 FeCO3+5 H2O
“NO−
2 +2 Fe(OH)3+2
+
HCO−
3 +2 H
Pyrolobus, Pyrobaculum,
Aquifex, Sulfolobus,
Acidianus, Metallosphaera
Aquifex, Sulfolobus,
Acidianus, Metallosphaera
Ferroglobus
are able to grow by oxidation of S0, sulfides (A.
brieleyi is able to grow by leaching of sulfidic
ores), H2 and organic matter. Under anaerobic
conditions they are able to reduce elemental sulfur
with H2 as an electron donor producing H2S
(Segerer et al., 1985; Table 3). Acidianus grows in
the presence of up to 4% salt. In agreement,
strains have been isolated from a marine hydrothermal system (Segerer et al., 1986). Stygiolobus is a strictly anaerobic extreme acidophile,
growing obligate chemolithoautotrophically by reduction of S0 with H2 (Segerer et al., 1991).
5.2. Neutrophiles and moderate acidophiles
Communities of neutrophilic and slightly
acidophilic hyperthermophiles are found in terrestrial solfataric fields, submarine hydrothermal systems and deep oil reservoirs (Stetter et al., 1993).
Most of them are strict anaerobes. Terrestrial
solfataric fields contain members of the genera
Thermoproteus,
Pyrobaculum,
Thermofilum,
Methanothermus, Desulfurococcus, Sulfophobococcus and Thermosphaera (Table 4). Cells of Thermoproteus, Pyrobaculum and Thermofilum are
almost rectangular rods. The diameters of Thermofilum cells are only about 0.17–0.35 mm while
those of Pyrobaculum and Thermoproteus are between 0.4 and 0.50 mm (Zillig et al., 1983a).
Spheres at the ends of around 50% of the cells,
described as ‘golf clubs’, can be seen under the
microscope, using normal microscopic slides and
cover glasses. However, only up to 2% of the cells
show ‘golf clubs’, if microslides or poly-lysine
coated glasses are used. The reason for this behaviour remains unclear at the moment (Huber et
al., unpublished). Thermoproteus neutrophilus,
Thermoproteus tenax and Pyrobaculum islandicum
are able to grow chemolithoautotrophically by
anaerobic reduction of S0 by H2 (Table 3). In
addition, T. tenax and P. islandicum are facultative heterotrophic sulfur respirers. As an exception, Pyrobaculum aerophilum is a marine
organism able to grow anaerobically by reduction
of nitrate by H2 and on H2 and O2 under microaerobic conditions (Völkl et al., 1993). Strains
of Pyrobaculum organotrophum, Thermoproteus
87
85
100
83
85
88
98
88
80
85
75
56
70
60
65
65
84
45
55
67
Thermococcus celer
Thermococcus alcaliphilus
Pyrococcus furiosus
Archaeoglobus fulgidus
Ferroglobus placidus
Methanothermus sociabilis
Methanopyrus kandleri
Methanococcus igneus
Thermotoga maritima
Aquifex pyrophilus
m, marine; t, terrestrial.
88
100
100
88
105
106
85
90
92
88
70
74
75
70
82
90
70
70
65
75
Thermoproteus tenax
Pyrobaculum islandicum
Pyrobaculum aerophilum
Thermofilum pendens
Pyrodictium occultum
Pyrolobus fumarii
Desulfurococcus mobilis
Aeropyrum pernix
Staphylothermus marinus
‘‘Thermodiscus maritimus’’
a
75
75
88
80
60
50
60
57
Sulfolobus acidocaldarius
Metallosphaera sedula
Acidianus infernus
Stygiolobus azoricus
95
90
91
110
97
95
95
93
90
105
97
103
104
95
110
113
95
100
98
98
85
80
95
89
Optimum Maximum
Temperature (°C)
Growth conditions
Minimum
Species
5.4 – 7.5
5.5 – 9
5 – 7.5
5.5 – 7
5.5 – 7.5
5.5 – 7.5
6 – 8.5
4–7
6.5 – 10.5
5–9
2.5 – 6
5–7
5.8 – 9
4 – 6.5
5–7
4–6
4.5 – 7
5–9
4.5 – 8.5
5–7
1–5
1 – 4.5
1.5 – 5
1 – 5.5
pH
ae
an
an
an
an
an
an
an
an
an
an
an
ae/an
an
an
an
an
ae
an
an
ae
ae
ae/an
an
Aerobic (ae)
Anaerobic (an)
Table 4
Growth conditions and morphological and biochemical features of hyperthermophiles
m
m
m
m
t
m
m
m
m
m
t
t
m
t
m
m
t
m
m
m
t
t
t
t
Habitata
40
46
31
60
33
46
43
57
43
38
56
46
52
57
62
53
51
67
35
49
37
45
31
38
DNA mol% G+C
Rods
Rods with sheath
Irregular cocci
Rods in chains
Rods in clusters
Irregular cocci
Irregular cocci
Cocci
Cocci
Cocci
Regular rods
Regular rods
Regular rods
Slender regular rods
Discs with fibres
Lobed cocci
Cocci
Irregular cocci
Cocci in aggregates
Discs
Lobed cocci
Cocci
Lobed cocci
Lobed cocci
Morphology
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
45
46
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
Fig. 2. Electron micrographs of hyperthermophilic microorganisms (bar: a and b: 1.0 mm; c and d: 0.5 mm). Preparation: a and c:
scanning electron micrograph; b and d: freeze etching; a: A. pyrophilus; b: P. fumarii; c: A. 6eneficus; d: M. sedula.
uzoniensis and Thermofilum are obligate heterotrophs growing on organic substrates by sulfur
respiration. Both Methanothermus species grow
chemolithoautotrophically by reduction of CO2
by H2 producing methane. So far, these rodshaped methanogens were isolated only from hot
springs in the Kerlingarfjöll mountains in Iceland.
Possibly this genus is endemic for this area (Stetter et al., 1981; Lauerer et al., 1986). The coccoid-
shaped Desulfurococcus, Sulfophobococcus and
Thermosphaera are obligate heterotrophs. While
Desulfurococcus is a sulfur respirer, Sulfophobococcus and Thermosphaera are inhibited by elemental sulfur (Hensel et al., 1997; Huber et al.,
1998).
Many terrestrial and submarine hydrothermal
fields contain members of the bacterial genus
Thermotoga which are rod-shaped cells sur-
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
rounded by a characteristic sheath-like structure
(‘Toga’) overballooning at the ends (Table 4). The
Toga contains porins and is most likely homologous to the outer membrane of gramnegative
bacteria (Rachel et al., 1990). Thermotoga ferments various carbohydrates like glucose, starch
and xylanes, forming acetate, L-lactate, H2 and
CO2 as end products (Huber et al., 1986). The
rod-shaped chemolithoautotrophic Aquifex pyrophilus (Fig. 2a) represents the deepest phylogenetic branch within the bacterial domain (Fig. 1),
achieving the highest growth temperature within
the Bacteria (Table 2; Burggraf et al., 1992).
Aquifex gains energy by oxidation of hydrogen or
sulfur under microaerobic conditions (Huber et
al., 1992). Alternatively, Aquifex is able to use
nitrate as electron acceptor (Table 3).
Many archaeal hyperthermophilic genera have
been isolated from marine environments. Pyrolobus fumarii (Fig. 2b) is the organism with the
highest growth temperature of all living organisms
known so far (113°C; Blöchl et al., 1997). It is a
facultative aerobic obligate chemolithotroph. Pyrolobus gains energy by reduction of nitrate,
S2O23 − or O2, using H2 as electron donor forming
ammonia, H2S or water, respectively (Table 3).
Members of Pyrodictium and Methanopyrus grow
at temperatures up to 110°C. Cells of Pyrodictium
are disk-shaped and are connected by a network
of ultrathin hollow tubules (‘canullae’). Strains of
Pyrodictium are usually chemolithoautotrophs
gaining energy by reduction of S0 by H2. Pyrodictium abyssi is a heterotroph growing by peptide
fermentation (Pley et al., 1991). Methanopyrus
kandleri is a rod-shaped methanogen with a pseudomurein cell wall covered by an S-layer. Representing the deepest and shortest phylogenetic
branch within the Archaea (Fig. 1), members of
Methanopyrus are strict chemolithoautotrophs
that grow optimally at 100°C with a doubling
time of 50 min (Huber et al., 1989b; Kurr et al.,
1991). In contrast to all other members of Archaea, Methanopyrus species contain 2,3-di-O-geranylgeranyl-sn-glycerol
as
the
dominating
membrane lipid (Hafenbradl et al., 1993). Further
marine methanogenic hyperthermophiles are
Methanococcus igneus and Methanococcus jan-
47
naschii (Table 2). Members of Staphylothermus
and Thermodiscus are coccoid and disk-shaped
strictly heterotrophic sulfur respirers. They gain
energy by fermentation of peptides, amino acids
and sugars, forming fatty acids, CO2 and H2.
Hydrogen is inhibitory to growth and can be
removed by gassing with N2 (Fiala et al., 1986).
Alternatively, hydrogen inhibition can be prevented by the addition of S0, where upon H2S is
formed instead of H2. In contrast, growth of a
further member of the Desulfurococcaceae, Stetteria hydrogenophila, strictly depends on the presence of hydrogen. Sulfur or thiosulfate are used as
external electron acceptors (Jochimsen et al.,
1997). Aeropyrum pernix represents the first aerobic member of the Desulfurococcaceae (Sako et
al., 1996; Burggraf et al., 1997a). It uses complex
organic substrates and growth is stimulated by the
addition of thiosulfate. Pyrococcus strains (especially Pyrococcus furiosus) grow on a great variety
of organic compounds like proteins, carbohydrates, and complex organic substrates. P. furiosus and Pyrococcus abyssi are able to ferment
pyruvate, forming acetate, H2 and CO2 (Schäfer
and Schönheit, 1992). Pyrococcus and Thermococcus species were found in oil reservoirs (Stetter et
al., 1993). Thermococcus alcaliphilus is able to
grow up to pH 10.5, while Thermococcus chitonophagus represents a novel hyperthermophilic
chitin degrader (Huber et al., 1995a; Keller et al.,
1995). Thermococcus peptonophilus and Thermococcus fumicolans require peptides as carbon
sources (González et al., 1995; Godfroy et al.,
1996). Archaeal coccoid sulfate reducers are members of Archaeoglobus. Some species occur within
hot oil reservoirs and may be responsible for the
presence of H2S (‘reservoir souring’; Stetter et al.,
1993). In the laboratory, growth is stimulated by
crude oil. Archaeoglobus fulgidus and ‘Archaeoglobus lithotrophicus’ are able to gain energy
by reduction of SO24 − by H2. In contrast, Archaeoglobus 6eneficus (Fig. 2c) is a chemolithoautotrophic sulfite reducer. It is unable to use sulfate
as electron acceptor (Huber et al., 1997). Archaeoglobus profundus is an obligate heterotroph.
A. fulgidus shares several coenzymes with
48
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
methanogens. Ferroglobus placidus (Hafenbradl et
al., 1996), which is related to Archaeoglobus, exhibits a new energy yielding reaction for Archaea,
the anaerobic iron oxidation (Table 3). Nitrate
serves as electron acceptor. In the presence of H2
as electron donor it can be replaced by
thiosulfate.
6. Biotechnological implications
As a consequence the growth temperatures of
hyperthermophiles, their enzymes are highly temperature stable, making them attractive for new
biotechnological applications. Most of the hyperthermophilic enzymes purified so far were isolated
from Thermotoga maritima, Pyrococcus furiosus
or closely related strains (Leuschner and
Antranikian, 1995). This includes extracellular enzymes like amylases, proteases, xylanases or pullulanases but also intracellular enzymes like
dehydrogenases, oxidoreductases, and DNA polymerases. Some of them show no significant loss of
activity after several hours at 100°C and are even
active at temperatures that exceed the temperature
maxima of the organism they have been isolated
from (Koch et al., 1991; Leuschner and
Antranikian, 1995). A major commercial application of a thermostable enzyme so far is the polymerase-chain-reaction (PCR) employing the DNA
polymerase of Thermus aquaticus (Saiki et al.,
1988). In the future the whole variety of hyperthermophilic isolates may serve as a source of
enzymes with very different properties. For example, the DNA polymerase of P. furiosus (Pfu) as
well as that of T. maritima (UITma™) with their
higher fidelity due to proofreading are already
commercially available now. In view of an enormous, so far uncultivated variety of hyperthermophiles (Barns et al., 1994), a further strategy to
obtain novel enzymes could be based on DNA
extraction directly from the environment, followed by gene expression, robot screening, and
cloning in production strains of (mesophilic) microorganisms (Robertson et al., 1996).
By comparison of sequences of homologous
enzymes properties can be assigned to specific
gene segments which may be important for futural
enzyme design.
In addition, cultures of viable hyperthermophiles may be used directly in technical processes. In a novel biological flue gas
desulfurization, hyperthermophilic autotrophic
sulfite reducers are used in power plants or chemical factories. In this process, sulfur dioxide is first
washed out from the flue gases. In an anaerobic
reactor, hyperthermophiles like Archaeoglobus
6eneficus (Fig. 2c) reduce SO2 to H2S, using H2 or
methanol as electron donor. Simultaneously,
heavy metals are removed from the sulfur-rich
water due to the precipitation of metal sulfides. In
a second (aerobic) reactor, H2S is oxidised to
elemental sulfur. The result is a highly pure and
valuable end product, elemental sulfur, while in
the standard process of desulfurication of flue
gases gypsum is produced. Due to the contamination with heavy metals it is a waste material and
has to be deposited.
In biohydrometallurgy representatives of Sulfolobus, Acidianus and Metallosphaera are applied
in leaching processes. This includes the treatment
of refractory gold ores (by removing the pyrite or
arsenopyrite), the leaching of low grade ores (e.g.
copper, zinc ores) or the removal of pyrite from
coal. The high turnovers, compared to mesophilic
leaching organisms (Huber et al., 1989a; Huber
and Stetter, 1991) recommend hyperthermophiles
even for reactor leaching of ore concentrates in
continuous processes. Due to self-heating during
the biologic leaching process high temperatures
arise. Within heaps temperatures up to 80°C have
been measured (Beck, 1967) and in reactor leaching the costs for cooling can be saved by using the
archaeal hyperthermophilic leaching organisms.
7. Perspectives
There is an unanticipated diversity of species of
hyperthermophiles within high temperature environments. This is evident by 16S rRNA sequence
diversity and by unusual physiologic properties.
Under the view of ecology within their biotopes,
hyperthermophiles are either primary producers
or consumers of organic matter. Energy conservation in primary producers occurs by anaerobic
and aerobic types of respiration, in which molecu-
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
lar hydrogen is mainly used as an electron donor.
Consumers gain energy either by anaerobic or
aerobic types of respiration or by fermentation.
Based on their unique properties, hyperthermophiles may play an important role in technical
processes in the future.
Acknowledgements
We wish to thank Reinhard Rachel for the
preparation of the electron micrographs. The
work presented from our laboratory was supported by grants of the Deutsche Forschungsgemeinschaft, the Bundesministerium für Forschung
und Technologie and the Fonds der Chemischen
Industrie.
References
Barns, S.M., Fundyga, R.E., Jeffries, M.W., Pace, N.R., 1994.
Remarkable archaeal diversity detected in a Yellowstone
National Park hot spring environment. Proc. Natl. Acad.
Sci. USA 91, 1609 – 1613.
Beck, J.V., 1967. The role of bacteria in copper mining operations. Biotech. Bioeng. 9, 487–497.
Blöchl, E., Rachel, R., Burggraf, S., Hafenbradl, D., Jannasch,
H.W., Stetter, K.O., 1997. Pyrolobus fumarii, gen. and sp.
nov., represents a novel group of archaea, extending the
upper temperature limit for life to 113°C. Extremophiles 1,
14– 21.
Bonch-Osmolovskaya, E.A., Slesarev, A.I., Miroshnichenko,
M.L., Svetlichnaya, T.P., Alexeyev, V.A., 1985. Characteristics of Desulfurococcus amylolyticus n. sp., a new extreme
thermophilic archaebacterium from hot volcanic vents of
Kamchatka and Kunashir. Microbiologyia 57, 78–85 (in
Russian).
Bonch-Osmolovskaya, E.A., Miroshnichenko, M.L., Kostrikina, N.A., Chernych, N.A., Zavarzin, G.A., 1990. Thermoproteus uzoniensis sp. nov., a new extremely thermophilic
archaebacterium from Kamchatka continental hot springs.
Arch. Microbiol. 154, 556–559.
Brierley, C.L., Brierley, J.A., 1973. A chemolithoautotrophic
and thermophilic microorganism isolated from an acidic
hot spring. Can. J. Microbiol. 19, 193–198.
Brierley, C.L., Brierley, J.A., 1982. Anaerobic reduction of
molybdenum Sulfolobus species. Zentralbl. Bakteriologie
Hygiene Abteilung Originale C3, 289–294.
Brock, T.D., 1978. Thermophilic Microorganisms and Life at
High Temperatures. Springer-Verlag, New York.
Brock, T.D., 1986. Thermophiles: General, Molecular and
Applied Microbiology. Wiley, New York.
49
Brock, T.D., Brock, K.M., Belly, R.T., Weiss, R.L., 1972.
Sulfolobus: a new genus of sulfur-oxidizing bacteria living
at low pH and high temperature. Arch. Microbiol. 84,
54 – 68.
Burggraf, S., Jannasch, H.W., Nicolaus, B., Stetter, K.O.,
1990a. Archaeoglobus profundus sp. nov. represents a new
species within the sulfate-reducing archaebacteria. Syst.
Appl. Microbiol. 13, 24 – 28.
Burggraf, S., Fricke, H., Neuner, A., Kristjansson, J., Rouvier,
P., Mandelco, L., Woese, C.R., Stetter, K.O., 1990b.
Methanococcus igneus sp. nov., a novel hyperthermophilic
methanogen from a shallow submarine hydrothermal system. Syst. Appl. Microbiol. 13, 263 – 269.
Burggraf, S., Olsen, G.J., Stetter, K.O., Woese, C.R., 1992. A
phylogenetic analysis of Aquifex pyrophilus. Syst. Appl.
Microbiol. 15, 352 – 356.
Burggraf, S., Huber, H., Stetter, K.O., 1997a. Reclassification
of the crenarchaeal orders and families in accordance with
16S rRNA sequence data. Int. J. Syst. Bacteriol. 47, 657 –
660.
Burggraf, S., Heyder, P., Eis, N., 1997b. A pivotal archaea
group. Nature 385, 780.
Erauso, G., Reysenbach, A.-L., Godfroy, A., Meunier, J.-R.,
Crump, B., Partensky, F., Baross, J.A., Marteinsson, V.,
Barbier, G., Pace, N.R., Prieur, D., 1993. Pyrococcus
abyssi sp. nov., a new hyperthermophilic archaeon isolated
from a deep-sea hydrothermal vent. Arch. Microbiol. 160,
338 – 349.
Fiala, G., Stetter, K.O., 1986. Pyrococcus furiosus sp. nov.
represents a novel genus of marine heterotrophic archaebacteria growing optimally at 100°C. Arch. Microbiol. 145,
56 – 61.
Fiala, G., Stetter, K.O., Jannasch, H.W., Langworthy, T.A.,
Madon, J., 1986. Staphylothermus marinus sp. nov. represents a novel genus of extremely thermophilic submarine
heterotrophic archaebacteria growing up to 98°C. Syst.
Appl. Microbiol. 8, 106 – 113.
Fuchs, T., Huber, H., Teiner, K., Burggraf, S., Stetter, K.O.,
1995. Metallosphaera prunae, sp. nov., a novel metal-mobilizing thermoacidophilic Archaeum, isolated from a uranium mine in Germany. Syst. Appl. Microbiol. 18,
560 – 566.
Fuchs, T., Huber, H., Burggraf, S., Stetter, K.O., 1996. 16S
rDNA-based phylogeny of the archaeal order Sulfolobales
and reclassification of Desulfurolobus ambi6alens as Acidianus ambi6alens comb. nov. System. Appl. Microbiol. 19,
56 – 60.
Godfroy, A., Meunier, J.-R., Guezennec, J., Lesongeur, F.,
Raguénès, G., Rimbault, A., Barbier, G., 1996. Thermococcus fumicolans sp. nov., a new hyperthermophilic archaeon isolated from a deep-sea hydrothermal vent in the
north Fiji Basin. Int. J. System. Bacteriol. 46, 1113 – 1119.
González, J.M., Kato, C., Horikoshi, K., 1995. Thermococcus
peptonophilus sp. nov., a fast-growing, extremely thermophilic archaebacterium isolated from deep-sea hydrothermal vents. Arch. Microbiol. 164, 159 – 164.
50
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
Grogan, D., Palm, P., Zillig, W., 1990. Isolate B 12, which
harbours a virus-like element, represents a new species of
the archaebacterial genus Sulfolobus, Sulfolobus shibatae,
sp. nov. Arch. Microbiol. 154, 594–599.
Hafenbradl, D., Keller, M., Thiericke, R., Stetter, K.O., 1993.
A novel unsaturated archaeal ether core lipid from the
hyperthermophile Methanopyrus kandleri. Syst. Appl. Microbiol. 16, 165 – 169.
Hafenbradl, D., Keller, M., Dirmeier, R., Rachel, R.,
Roßnagel, P., Burggraf, S., Huber, H., Stetter, K.O., 1996.
Ferroglobus placidus gen. nov., sp. nov., a novel hyperthermophilic archaeum that oxidizes Fe2 + at neutral pH under
anoxic conditions. Arch. Microbiol. 166, 308–314.
Hensel, R., Matussek, K., Michalke, K., Tacke, L., Tindall,
B.J., Kohlhoff, N., Siebers, B., Dielenschneider, J., 1997.
Sulfophobococcus zilligii gen. nov., spec. nov., a novel
hyperthermophilic archaeum isolated from hot alkaline
springs of Iceland. Syst. Appl. Microbiol. 20, 102–110.
Huber, G., Stetter, K.O., 1991. Sulfolobus metallicus, sp. nov.,
a novel strictly chemolithoautotrophic thermophilic archaeal species of metal mobilizers. Syst. Appl. Microbiol.
14, 372 – 378.
Huber, G., Spinnler, C., Gambacorta, A., Stetter, K.O., 1989a.
Metallosphaera sedula gen. and sp. nov., represents a new
genus of aerobic, metal-mobilizing, thermoacidophilic
archeabacteria. Syst. Appl. Microbiol. 12, 38–47.
Huber, H., Thomm, M., König, H., Thies, G., Stetter, K.O.,
1982. Methanococcus thermolithotrophicus, a novel thermophilic lithotrophic methanogen. Arch. Microbiol. 132,
47– 50.
Huber, H., Jannasch, H., Rachel, R., Fuchs, T., Stetter, K.O.,
1997. Archaeoglobus 6eneficus sp. nov., a novel facultative
chemolithoautotrophic hyperthermophilic sufite reducer,
isolated from a abyssal black smoker. Syst. Appl. Microbiol. 20, 374 – 380.
Huber, R., Langworthy, T.A., König, H., Thomm, M., Woese,
C.R., Sleytr, U.B., Stetter, K.O., 1986. Thermotoga maritima sp. nov. represents a new genus of unique extremely
thermophilic eubacteria growing up to 90°C. Arch. Microbiol. 144, 324 – 333.
Huber, R., Kristjansson, J.K., Stetter, K.O., 1987. Pyrobaculum
gen. nov. a new genus of neutrophilic, rod-shaped archaebacteria from continental solfataras growing optimally at
100°C. Arch. Microbiol. 149, 95–101.
Huber, R., Kurr, M., Jannasch, H.W., Stetter, K.O., 1989b. A
novel group of abyssal methanogenic archaebacteria
(Methanopyrus) growing at 110°C. Nature 342, 833–834.
Huber, R., Woese, C.R., Langworthy, T.A., Fricke, H., Stetter,
K.O., 1989c. Thermosipho africanus gen. nov., represents a
new genus of thermophilic eubacteria within the ‘‘Thermotogales’’. Syst. Appl. Microbiol. 12, 32–37.
Huber, R., Stoffers, P., Cheminee, J.L., Richnow, H.H., Stetter,
K.O., 1990a. Hyperthermophilic archaebacteria within the
crater and open-sea plume of erupting Macdonald
Seamount. Nature 345, 179–182.
Huber, R., Woese, C.R., Langworthy, T.A., Kristjansson, J.K.,
Stetter, K.O., 1990b. Fer6idobacterium islandicum sp. nov.,
a new extremely thermophilic eubacterium belonging to the
‘‘Thermotogales’’. Arch. Microbiol. 154, 105 – 111.
Huber, R., Wilharm, T., Huber, D., Trincone, A., Burggraf, S.,
König, H., Rachel, R., Rockinger, I., Fricke, H., Stetter,
K.O., 1992. Aquifex pyrophilus gen. nov. sp. nov., represents
a novel group of marine hyperthermophilic hydrogen-oxidizing bacteria. Syst. Appl. Microbiol. 15, 340 – 351.
Huber, R., Stöhr, J., Hohenhaus, S., Rachel, R., Burggraf, S.,
Jannasch, H.W., Stetter, K.O., 1995a. Thermococcus chitonophagus sp. nov., a novel, chitin-degrading, hyperthermophilic archaeum from a deep-sea hydrothermal vent
environment. Arch. Microbiol. 164, 255 – 264.
Huber, R., Burggraf, S., Mayer, T., Barns, S.M., Roßnagel, P.,
Stetter, K.O., 1995b. Isolation of a hyperthermophilic archaeum predicted by in situ RNA analysis. Nature 376,
57 – 58.
Huber, R., Dyba, D., Huber, H., Burggraf, S., Rachel, R., 1998.
Characterization of the sulfur-inhibited Thermosphaera aggregans sp. nov., a new genus of hyperthermophilic archaea
isolated after its prediction from environmentally derived
16S rRNA sequences. Int. J. Syst. Bacteriol 48, 31 – 38.
Iwabe, N., Kuma, K., Hasegawa, M., Osawa, S., Miyata, T.,
1989. Evolutionary relationship of archaebacteria, eubacteria and eucaryotes inferred from phylogenetic trees of
duplicated genes. Proc. Natl. Acad. Sci. USA 86, 9355 –
9359.
Jannasch, H.W., Huber, R., Belkin, S., Stetter, K.O., 1988.
Thermotoga neapolitana, sp. nov. of the extremely thermophilic, eubacterial genus Thermotoga. Arch. Microbiol.
150, 103 – 104.
Jochimsen, B., Peinemann-Simon, S., Völker, H., Stüben, D.,
Botz, R., Stoffers, P., Dando, P.R., Thomm, M., 1997.
Stetteria hydrogenophila, gen. nov. and sp. nov., a novel
mixotrophic sulfur-dependent Crenarchaeote isolated from
Milos, Greece. Extremophiles 1, 67 – 73.
Jones, W.J., Leigh, J.A., Mayer, F., Woese, C.R., Wolfe, R.S.,
1983. Methanococcus jannaschii sp. nov., an extremely thermophilic methanogen from a submarine hydrothermal vent.
Arch. Microbiol. 136, 254 – 261.
Keller, M., Braun, F.-J., Dirmeier, R., Hafenbradl, D.,
Burggraf, S., Rachel, R., Stetter, K.O., 1995. Thermococcus
alcaliphilus sp. nov., a new hyperthermophilic archaeum,
rowing on polysulfide at alkaline pH. Arch. Microbiol. 164,
390 – 395.
Kobayashi, T., Kwak, Y.S., Akiba, T., Kudo, T., Horikoshi,
K., 1994. Thermococcus profundus sp. nov., a new hyperthermophilic archaeon isolated from a deep-sea hydrothermal vent. Syst. Appl. Microbiol. 17, 232 – 236.
Koch, R., Spreinat, A., Lemke, K., Antranikian, G., 1991.
Purification and properties of a hyperthermoactive a-amylase from the archaebacterium Pyrococcus woesei. Arch.
Microbiol. 155, 572 – 578.
Kurr, M., Huber, R., König, H., Jannasch, H.W., Fricke, H.,
Trincone, A., Kristjansson, J.K., Stetter, K.O., 1991.
Methanopyrus kandleri gen. and sp. nov., represents a novel
group of hyperthermophilic methanogens, growing at
110°C. Arch. Microbiol. 156, 239 – 247.
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
Lauerer, G., Kristjansson, J.K., Langworthy, T.A., König, H.,
Stetter, K.O., 1986. Methanothermus sociabilis sp. nov., a
second species within the Methanothermaceae growing at
97°C. Syst. Appl. Microbiol. 8, 100–105.
Leuschner, C., Antranikian, G., 1995. Heat-stable enzymes
from extremely thermophilic and hyperthermophilic microorganisms. World J. Microbiol. Biotechnol. 11, 95–114.
Marsh, R.M., Norris, P.R., 1985. The isolation of some thermophilic, autotrophic iron- and sulfur-oxidizing bacteria.
FEMS Microbiol. Lett. 17, 311–315.
Miroshnichenko, M.L., Bonch-Osmoslovskaya, E.A., Neuner,
A., Kostrikina, N.A., Chernych, N.A., Alexeyev, V.A.,
1989. Thermococcus stetteri sp. nov. a new extremely thermophilic marine sulfur-metabolizing archaebacterium.
Syst. Appl. Microbiol. 12, 257–262.
Neuner, A., Jannasch, H.W., Belkin, S., Stetter, K.O., 1990.
Thermococcus litoralis sp. nov. a new species of extremely
thermophilic marine archaebacteria. Arch. Microbiol. 153,
205 – 207.
Patel, B.K.C., Morgan, H.W., Daniel, R.M., 1985. Fer6idobacterium nodosum gen. nov. and spec. nov., a new
chemoorganotrophic, caldoactive, anaerobic bacterium.
Arch. Microbiol. 141, 63–69.
Pley, U., Schipka, J., Gambacorta, A., Jannasch, J.W., Fricke,
H., Rachel, R., Stetter, K.O., 1991. Pyrodictium abyssi sp.
nov. represents a novel heterotrophic marine archaeal hyperthermophile growing at 110°C. Syst. Appl. Microbiol.
14, 245 – 253.
Rachel, R., Engel, A.M., Huber, R., Stetter, K.O., Baumeister,
W., 1990. A porin-type protein is the main constituent of
the cell envelope of the ancestral eubacterium Thermotoga
maritima. FEBS Lett. 262, 64–68.
Ravot, G., Magot, M., Fardeau, M.-L., Patel, B.K.C., Prensier, G., Egan, A., Garcia, J.-L., Ollivier, B., 1995. Thermotoga elfii sp. nov., a novel thermophile bacterium from
an African oil-producing well. Int. J. Syst. Bacteriol. 45,
308 – 314.
Robertson, D.E., Mather, E.J., Swanson, R.V., Marrs, B.L.,
Short, J.M., 1996. The discovery of new biocatalysts from
microbial diversity. Soc. Ind. Microbiol. News 46, 3–8.
Saiki, R.K., Gelfand, D.H., Stoffel, S., Scharf, S.J., Higuchi,
R., Horn, G.T., Mullis, K.B., Erlich, H.A., 1988. Primerdirected enzymatic amplification of DNA with thermostable DNA polymerase. Science 239, 487–491.
Sako, Y., Nomura, N., Uchida, A., Ishida, Y., Morii, H.,
Koga, Y., Hoaki, T., Maruyama, T., 1996. Aeropyrum
pernix gen. nov., sp. nov., a novel aerobic hyperthermophilic archaeon growing at temperatures up to 100°C.
Int. J. Syst. Bacteriol. 10, 1070–1077.
Schäfer, T., Schönheit, P., 1992. Maltose fermentation to
acetate, CO2 and H2 in the anaerobic hyperthermophilic
archaeon Pyrococcus furiosus: evidence for the operation
of a novel sugar fermentation pathway. Arch. Microbiol.
158, 188 – 202.
Segerer, A., Stetter, K.O., Klink, F., 1985. Two contrary
modes of chemolithoautotrophy in the same archaebacterium. Nature 313, 787–789.
51
Segerer, A., Neuner, A., Kristjansson, J.K., Stetter, K.O.,
1986. Acidianus infernus gen. nov., sp. nov., and Acidianus
brierleyi comb. nov.: facultatively aerobic, extremely
acidophilic thermophilic sulfur-metabolizing archaebacteria. J. Bacteriol. 36, 559 – 564.
Segerer, A.H., Trincone, A., Gahrtz, M., Stetter, K.O., 1991.
Stygiolobus azoricus gen. and sp. nov., represents a novel
genus of anaerobic, extremely thermoacidophilic archaea
of the order Sulfolobales. J. Bacteriol. 41, 495 – 501.
Stetter, K.O., 1986. Diversity of extremely thermophilic archaebacteria. In: Brock, T.D. (Ed.), Thermophiles: General, Molecular, and Applied Microbiology. Wiley, New
York, pp. 40 – 74.
Stetter, K.O., 1988. Archaeoglobus fulgidus gen. nov., sp. nov.:
a new taxon of extremely thermophilic archaebacteria.
Syst. Appl. Microbiol. 10, 172 – 173.
Stetter, K.O., 1992. Life at the upper temperature border. In:
Tran Thanh Van, J., Tran Thanh Van, K., Mounolou,
J.C., Schneider, J., McKay, C. (Eds.), Frontiers of Life.
Gif-sur-Yvette: Editions Frontières France, pp. 195 – 219.
Stetter, K.O., 1994. The lesson of Archaebacteria. In: Bengtson, S. (Ed.), Nobel Symposium, vol. 84. Columbia University Press, New York, pp. 143 – 151.
Stetter, K.O., Zillig, W., 1985. Thermoplasma and the thermophilic sulfur-dependent archaebacteria. In: Wolfe, R.S.,
Woese, C.R. (Eds.), The Bacteria, vol. 8. Academic Press,
New York, pp. 85 – 170.
Stetter, K.O., Thomm, M., Winter, J., Wildgruber, G., Huber,
H., Zillig, W., Janecovic, D., König, H., Palm, P., Wunderl, S., 1981. Methanothermus fer6idus, sp. nov., a novel
extremely thermophilic methanogen isolated from an Icelandic hot spring. Zentralbl. für Bakteriologie und Hygiene
I. Abteilung Originale C2, 166 – 178.
Stetter, K.O., König, H., Stackebrandt, E., 1983. Pyrodictium
gen. nov., a new genus of submarine disc-shaped sulfur
reducing archaebacteria growing optimally at 105°C. Syst.
Appl. Microbiol. 4, 535 – 551.
Stetter, K.O., Huber, R., Blöchl, E., Kurr, M., Eden, R.D.,
Fiedler, M., Cash, H., Vance, I., 1993. Hyperthermophilic
archaea are thriving in deep North Sea and Alaskan oil
reservoirs. Nature 300, 743 – 745.
Völkl, P., Huber, R., Drobner, E., Rachel, R., Burggraf, S.,
Trincone, A., Stetter, K.O., 1993. Pyrobaculum aerophilum
sp. nov., a novel nitrate-reducing hyperthermophilic archaeum. Appl. Environ. Microbiol. 59, 2918 – 2926.
Windberger, E., Huber, R., Trincone, A., Fricke, H., Stetter,
K.O., 1989. Thermotoga thermarum sp. nov. and Thermotoga neapolitana occuring in African continental solfataric
springs. Arch. Microbiol. 151, 506 – 512.
Woese, C.R., Fox, G.E., 1977. Phylogenic structure of the
prokaryotic domain: the primary kingdoms. Proc. Natl.
Acad. Sci. USA 74, 5088 – 5090.
Woese, C.R., Kandler, O., Wheelis, M.L., 1990. Towards a
natural system of organisms. Proposal for the domains
Archaea, Bacteria, and Eucarya. Proc. Natl. Acad. Sci.
USA 87, 4576 – 4579.
52
H. Huber, K.O. Stetter / Journal of Biotechnology 64 (1998) 39–52
Zillig, W., Stetter, K.O., Wunderl, S., Schulz, W., Priess, H.,
Scholz, I., 1980. The Sulfolobus– Caldariella group: taxonomy on the basis of the structure of DNA-dependent
RNA polymerases. Arch. Microbiol. 125, 259–269.
Zillig, W., Stetter, K.O., Schäfer, W., Janecovic, D., Wunderl, S., Holz, I., Palm, P., 1981. Thermoproteales: a
novel type of extremely thermoacidophilic anaerobic archaebacteria isolated from Icelandic solfataras. Zentralbl.
für Bakteriologie und Hygiene I. Abteilung Originale C2,
205 – 227.
Zillig, W., Stetter, K.O., Prangishvilli, C., Schäfer, W., Wunderl, S., Janecovic, D., Holz, I., Palm, P., 1982. Desulfurococcaceae, the second family of the extremely
thermophilic, anaerobic, sulfur-respiring Thermoproteales.
Zentralbl. für Bakteriologie und Hygiene I. Abteilung
Originale C3, 304 – 317.
Zillig, W., Gierl, A., Schreiber, G., Wunderl, S., Janecovic,
D., Stetter, K.O., Klenk, H.P., 1983a. The archaebacterium Thermofilum pendens represents a novel genus of
.
thermophilic, anaerobic sulfur-respiring Thermoproteales.
Syst. Appl. Microbiol. 4, 79 – 87.
Zillig, W., Holz, I., Janecovic, D., Schäfer, W., Reiter,
W.D., 1983b. The archaebacterium Thermococcus celer
represents a novel genus within the thermophilic branch
of the archaebacteria. Syst. Appl. Microbiol. 4, 88 – 94.
Zillig, W., Yeates, S., Holz, I., Böck, A., Gropp, F., Simon,
G., 1987a. Desulfurolobus ambi6alens, gen. nov. sp. nov.,
an autotrophic archaebacterium facultatively oxidizing or
reducing sulfur. Syst. Appl. Microbiol. 8, 197 – 203.
Zillig, W., Holz, I., Klenk, H.P., Trent, J., Wunderl, S.,
Janekovic, D., Imsel, E., Haas, B., 1987b. Pyrococcus
woesei sp. nov., an ultra-thermophilic marine archaebacterium, represents a novel order, Thermococcales. Syst.
Appl. Microbiol. 9, 62 – 70.
Zillig, W., Holz, I., Janecovic, D., Klenk, H.P., Imsel, E.,
Trent, J., Wunderl, S., Forjatz, V.H., Coutinho, R., Ferreira, T., 1990. Hyperthermus butylicus, a hyperthermophilic sulfur-reducing archaebacterium that ferments
peptides. J. Bacteriol. 172, 3959 – 3965.