F E M S Microbiology Reviews 75 (1990) 117-124
Published by Elsevier
F E M S R E 00133
Hyperthermophilic microorganisms
K . O . Steuer, G . F i a l a , G . H u b e r , R . H u b e r a n d A . Segerer
Lehrstuhl für Mikrobiologie, Universität Regensburg, Regensburg, F.R.G.
K e y words: Hyperthermophiles; T a x o n o m y
1. I N T R O D U C T I O N
T h e most extremely t h e r m o p h i l i c l i v i n g beings
k n o w n to date are bacteria g r o w i n g at temperatures between 80 a n d 110 ° C [ 1 - 3 ] . S o m e o f them
are so well adapted to the high temperatures that
they d o not even g r o w b e l o w 80 ° C [4]. A s a rule,
n o n o f these h y p e r t h e r m o p h i l i c bacteria are able
to g r o w at 60 ° C o r b e l o w . H y p e r t h e r m o p h i l e s are
o c c u r r i n g m a i n l y w i t h i n the archaebacterial k i n g d o m [5]; some o f them are also present w i t h i n the
eubacteria [6,7]. D u e to their existence w i t h i n
phylogenetically h i g h l y divergent groups, the lack
of closely related mesophiles, a n d their biotopes
existing already since the A r c h e a n age, hypertherm o p h i l e s m a y have adapted to the hot e n v i r o n ment already b i l l i o n s o f years ago.
2. B I O T O P E S
T h e h y p e r t h e r m o p h i l i c bacteria k n o w n at pre-
7 to 9) rich i n N a C l . A l s o m a n - m a d e hot e n v i r o n ments such as the b o i l i n g o u t f l o w s o f geothermal
power plants are suitable e n v i r o n m e n t s for hyperthermophiles [9]. S u b m a r i n e h y d r o t h e r m a l systems
are slightly a c i d i c to a l k a l i n e ( p H 5 to 8.5) a n d
n o r m a l l y c o n t a i n h i g h a m o u n t s o f N a C l a n d SO4 ~
due to the presence o f sea water ( T a b l e 1). D u e to
the l o w s o l u b i l i t y o f oxygen at h i g h temperatures
a n d the presence o f r e d u c i n g gases, most b i o t o p e s
of hyperthermophiles are anaerobic. W i t h i n c o n tinental solfataric fields, o x y g e n is o n l y present
w i t h i n the upper a c i d i c layer w h i c h appears
ochre-coloured due to the existence o f ferric i r o n
[8].
A l t h o u g h n o t g r o w i n g b e l o w 60 ° C , hyperthermophiles are able to survive at l o w temperatures
at least for years. S o m e o f the a n a e r o b i c hyperthermophiles are able to tolerate o x y g e n m u c h
better at l o w (non-growth) temperatures than at
high (growth) temperatures. T h i s p r o p e r t y m a y be
essential for dispersal o f these organisms t h r o u g h
oxygen-rich low-temperature areas.
sent have been isolated from s u b m a r i n e h y d r o thermal areas a n d from c o n t i n e n t a l solfataras. T h e
surface of the solfataras is u s u a l l y rich i n sulfate
3. T A X O N O M Y
a n d exhibits a n a c i d i c p H (0.5 to 6; [1,2]). I n the
BACTERIA
d e p t h , solfataras are less a c i d i c or even neutral
U p to n o w , about 35 different species o f hypert h e r m o p h i l i c bacteria are k n o w n . T h e y b e l o n g to
different taxa w i t h i n the eu- a n d archaebacteria
( T a b l e 2). W i t h i n the eubacteria, h y p e r t h e r m o philes are w i t h i n the T h e r m o t o g a l e s order, w h i c h
is the deepest phylogenetic b r a n c h - o f f based o n
16S r R N A sequences w i t h i n this k i n g d o m [7]. T h e
phylogenetic tree w i t h i n the archaebacterial k i n g -
( p H 5 to 7; [8]). Sometimes, solfataric fields m a y
also c o n t a i n some w e a k l y a l k a l i n e hot springs ( p H
Correspondence to: K . O . Steuer, Lehrstuhl für Mikrobiologie,
Institute for Biochemistry, Genetics and Microbiology, University of Regensburg, Universitätsstr. 31, P.O. Box 397, D-8400
Regensburg, F.R.G.
0168-6445/90/S03.50 © 1990 Federation of European Microbiological Societies
OF HYPERTHERMOPHILIC
dorn exhibits two m a i n branches: the b r a n c h c o n t a i n i n g methanogens
a n d halophiles a n d
the
b r a n c h of the sulfur m e t a b o l i z i n g archaebacteria
[7]. T h e latter consists almost exclusively of hyperthermophiles [3,7] w h i l e there are o n l y a few groups
of hyperthermophiles w i t h i n the other b r a n c h
(Archaeoglobales, Thermococcales, Methanothermaceae, Mc. jannaschii).
W i t h i n the sulfur
metabolizers, a c i d o p h i l i c (e.g. Sulfolobus,
Metallosphaera, Acidianus)
a n d n e u t r o p h i l i c (e.g. Pyrodictium, Desulfurococcus,
Staphylothermus,
Thermococcus) genera were discovered d u r i n g the last
years. Therefore, the o l d designation " T h e r m o a c i d o p h i l e s " w h i c h was p r i m a r i l y used to characterize the genera Sulfolobus a n d
Thermoplasma
[1] is not suitable a n y m o r e for the designation of
this b r a n c h .
3.1. Extremely
acidophilic
2
S ° and S " , f o r m i n g sulfuric a c i d ( T a b l e 3, 4).
M a n y Sulfolobus
isolates are facultative heterotrophs a n d a few, still u n n a m e d , are even strict
heterotrophs
(Stetter, u n p u b l i s h e d ) . T h e type
strain of Sulfolobus
acidocaldarius
( D S M 639)
shows excellent g r o w t h o n o r g a n i c matter [11].
A u t o t r o p h i c a l l y c u l t u r e d o n S ~ a n d S ° , however,
this strain shows o n l y extremely weak g r o w t h a n d
sulfuric acid f o r m a t i o n [ 1 2 - 1 4 ] . S o m e members of
the Sulfolobales like Metallosphaera
sedula
are
able to o x i d i z e sulfidic ores like pyrite, c h a l c o p y r i t e and sphalerite, f o r m i n g sulfuric a c i d and
s o l u b i l i z i n g the heavy metal ions ( T a b l e 3,4; [15]).
U n d e r m i c r o a e r o p h i l i c c o n d i t i o n s , Sulfolobus
is
able to reduce ferric i r o n a n d m o l y b d a t e , w h i c h
therefore act as electron acceptors u n d e r these
c o n d i t i o n s [16,17]. M e m b e r s o f the genus Sulfolobus grow o n l y at very l o w i o n i c strength a n d were
therefore not f o u n d w i t h i n the m a r i n e e n v i r o n ment ([11]; Segerer a n d Stetter, u n p u b l i s h e d ) .
M e m b e r s of the genus Acidianus
s i m i l a r to
Sulfolobus
are able to g r o w b y o x i d a t i o n of S ° ,
f o r m i n g sulfuric acid [18,19]. S o m e strains grow
also on sulfidic ores, but m u c h less efficient than
Metallosphaera
( T a b l e 4; [14]). In a d d i t i o n , m e m bers of Acidianus are able to g r o w b y anaerobic
o x i d a t i o n of H , using S ° as electron d o n o r ( T a b l e
4; [18]). A t h e r m o a c i d o p h i l i c isolate, w h i c h had
been tentatively n a m e d "Sulfolobus
ambiualens"
[20] was later described as Desulfurolobus
ambivafens,
representing a new genus [21]. B y
D N A : D N A h y b r i d i z a t i o n , however,
Desulfurolobus ambivalens shows a close r e l a t i o n s h i p to the
2
hyperthermophiles
E x t r e m e l y a c i d o p h i l i c hyperthermophiles
were
found up to n o w exclusively w i t h i n c o n t i n e n t a l
solfataric fields. T h e organisms are coccoid-shaped
strict a n d facultative aerobes. T h e y are
extreme
acidophiles due to their requirement of a c i d i c p H
(opt. a p p r o x . p H 3). Phylogenetically, they b e l o n g
to the archaebacterial genera
losphaera,
Acidianus,
Sulfolobus,
Metal-
a n d Desulfurolobus.
T h e less
extremely t h e r m o p h i l i c archaebacterium
plasma
2
Thermo-
is an extreme a c i d o p h i l e , too. It is a facul-
tative anaerobe o c c u r r i n g both i n s m o l d e r i n g c o a l
refuse piles a n d c o n t i n e n t a l solfataric fields [1,10].
M e m b e r s o f the
genus Sulfolobus
are
strict
aerobes g r o w i n g a u t o t r o p h i c a l l y b y o x i d a t i o n o f
Table 1
Biotopes of hyperthermophilic bacteria
Characteristics
Sites
Temperatures
pH
Presence of 0
Major gases and
sulfur compounds
2
Type of thermal area
Solfataric fields
Submarine hydrothermal systems
Steam-heated mud holes.
soils and surface waters;
deep hot springs; geothermal power plants
Up to 1 0 0 ° C
0.5 to 9
Surface oxic; depth anoxic
C 0 , CO, C H , S 0 , N H
Hot sediments and vents
2 _
2
4
4
+
4
Up to about 374 ° C
5 to 8.5
Anoxic
H , H S,S°,S0 2
2
2
3
Taxonomy of hyperthermophilic archaebäcteria
Order
Genus
Species
I. Eubacteria! kingdom
Thermotogales
Thermotoga
T. maritima
8
Thermosipho
Fervidobacterium
8
T. neapolitana
T. thermarum
T. africanus
F. nodosum
F. islandicum
II. Archaebacterial kingdom
Sulfolobales
Sulfolobus
S. acidocaldarius
S. solfataricus
Metallosphaera
M. sedula
Acidianus
A. infernus
A. brierleyi
Desulfurolobus
D. ambiualens
Thermoproteales
Thermoproteus
T. tenax
T. neutrophifus
Pyrobaculum
P. islandicum
P. organotrophum
Thermofilum
T. pendens
T. librum
Desulfurococcus
D. mobilis
D. mucosus
D. saccharovorans
Staphylothermus • S. marinus
Pyrodictialcs
Pyrodictium
P. occultum
P. brockii
P. abyssum
Tliermodiscus
T. maritimus
Thermococcales
Thermococcus
T. celer
T. stetteri
Fyrococcus
P. furiosus
P. woésii
Archaeoglobales
Archaeoglobus
A. fulgidus
A. profundus
Thermoplasmales
Thermoplasma
T. acidophilum
T. volcanium
Methanobacteriales Methanothermus
M. fervidus
M. sociabilis
Methanococcales
Methanococcus
M. thermolithotrap hi cus
M. jannaschii
8
8
b
b
8
' Growth only up to about 7 0 ° C mentioned due to their close
relationship to hyperthermophiles
Contain also mesophilic species.
f
b
type species o f Acidianus, Acidianus infernus [22].
M e m b e r s o f the genus Acidianus are able to grow
in the presence o f up to 4% salt. In agreement w i t h
this result, they also have been isolated (rarely)
from a m a r i n e h y d r o t h e r m a l system [19].
3.2. Slightly acidophilic and neutrophilic
hyperthermophiles
Slightly a c i d o p h i l i c a n d n e u t r o p h i l i c hyperthermophiles were found b o t h i n c o n t i n e n t a l solfataric
fields and i n s u b m a r i n e h y d r o t h e r m a l systems a n d
they show specific adaptations to their e n v i r o n ments. A l l of them are strict anaerobes. S o l f a t a r i c
fields c o n t a i n members o f the genera
Thermoproteus, Pyrobaculum,
Thermofilum,
Desulfurococcus,
a n d Methanothermus
( T a b l e 3; [9,23-26]). C e l l s o f
members of the genera Thermoproteus,
Pyrobaculum, and Thermofilum
are characteristically stiff
rods w i t h p r o t r u d i n g spheres ( " g o l f c l u b s " ) m a i n l y
at their ends, p o s s i b l y due to a m o d e o f b u d d i n g .
C e l l s of Thermofilum
are o n l y about 0.17 to 0.35
/ i m i n w i d t h a n d are therefore different from
Thermoproteus
and Pyrobaculum.
Thermoproteus
tenax, Thermoproteus
neutrophilus
and
Pyrobaculum islandicum are able to g r o w a u t o t r o p h i c a l l y b y
anaerobic r e d u c t i o n of S ° w i t h H
as electron
d o n o r [9,27]. Strains of Thermofilum
a n d Pyro2
baculum organotrophum
are obligate heterotrophs.
T h e y are g r o w i n g b y sulfur r e s p i r a t i o n , u s i n g different organic substrates ( T a b l e 4).
Thermofilum
pendens shows an obligate requirement for a l i p i d
fraction o f Thermoproteus
tenax.
Thermoproteus
tenax and Pyrobaculum islandicum are also able to
grow h e t e r o t r o p h i c a l l y b y sulfur r e s p i r a t i o n ( T a ble 4). A l s o i n solfataric fields c o c c o i d heterot r o p h i c organisms o c c u r w h i c h g a i n energy b y
respiring organic material u s i n g sulfur as electron
acceptor. T h e y b e l o n g to the genus
Desulfurococcus [25]. F r o m solfataras i n the southwest o f Icel a n d , rod-shaped methanogens g r o w i n g at temperatures up to 97 ° C ( T a b l e 3) were isolated [26,28].
T w o species are k n o w n : Methanothermus
fervidus
and Methanothermus
sociabilis, cells o f the latter
g r o w i n g i n clusters u p to 3 m m . B o t h species are
strict autotrophs, g a i n i n g energy b y r e d u c t i o n o f
C 0 b y H ( T a b l e 4). W i t h i n neutral c o n t i n e n t a l
hot springs i n D j i b o u t i , A f r i c a , the extremely therm o p h i l i c eubacterial species Thermotoga
thermarum was found, w h i c h grows o n l y at l o w i o n i c
strength ( T a b l e 3,4; [29]). M e m b e r s o f this g r o u p
are strictly anaerobic heterotrophs, g r o w i n g b y
fermentation o f carbohydrates. M o s t o f them are
found w i t h i n the m a r i n e biotopes, however.
2
Many
2
hyperthermophiles are a d a p t e d
to
the
Growth conditions and morphological and biochemical features of hyperthermophiles
Species
Growth conditions
Temperature ( ° C)
pH
Aerobic (ae)
Habitat
anaerobic (an) (marine (m)/
solfataric (s))
Minimum Optimum Maximum
Sulfo/obus acidocaldarius
Metallosphaera sedula
Acidianus infernus
D N A Morphology
(mol%
G-f C)
60
50
60
80
75
88
85
80
95
1 -5
ae
1 -4.5 ae
1.5-5
ae/an
s
s
s
37
45
31
Lobed cocci
Cocci
Lobed cocci
Thermoplasma uolcanium 33
60
67
1 -4
ae/an
s
38
Irregular cocci
Thermoproteus tenax
70
88
97
2.5-6
an
s
56
Pyrobaculum islandicum
74
100
103
5 -7
an
s
46
Pyrobaculum organotrophum
78
Thermofilum pendens
70
100
88
102
95
5 -7
an
4 -6.5 an
s
s
46
57
Desulfurococcus mobilis
Staphyhthermus marin us
70
65
85
92
95
98
4.5-7
an
4.5-8.5 an
s
m
51
35
Rods with terminally
protruding spheres
Rods with terminally
protruding spheres
Rods with terminally
protruding spheres
Slender rods with
terminal spheres
Cocci
Cocci in aggregates
Pyrodictium occultum
Pyrodictium abyssum
Thermodiscus maritimus
82
80
75
105
100
88
110
110
98
5 -7
an
4.7-7.5 an
5 -7
an
m
m
m
62
60
49
Discs with fibres
Discs with fibres
Discs
Thermococcus celer
Pyrococcus furiosus
75
70
87
100
97
103
4 -7
an
an
m
m
57
38
Cocci
Cocci
Archaeoglobus fulgidus
60
83
95
5.5-7.5 an
m
46
Irregular cocci
Methanothermus sociabiiis 65
88
97
5.5-7.5 an
s
33
Rods in clusters
Methanococcus jannaschii 50
85
86
5.5-6.5 an
m
31
Irregular cocci
Thermotoga maritima
Thermotoga therma rum
80
70
90
84
5.5-9
6 -9
m
s
46
40
Rods with sheath
Rods with sheath
55
55
5
m a r i n e thermal environments ( T a b l e 3). T h e y are
represented b y the genera Staphyhthermus,
Pyrodictium, Thermodiscus,
Thermococcus,
Pyrococcus,
Archaeoglobus,
a n d b y members o f the genera
Methanococcus
a n d Thermotoga
( T a b l e 3;
[3,4,6,30-34]). T h e organisms w i t h the highest
g r o w t h temperatures k n o w n are members o f the
genus Pyrodictium,
g r o w i n g u p to 1 1 0 ° C [4,35].
C e l l s o f Pyrodictium
are so well-adapted to h i g h
temperatures that they d o not even grow b e l o w
80 ° C ( T a b l e 3). C u l t u r e s o f Pyrodictium
grow i n
floes. Cells are disc-shaped a n d are connected b y a
network o f very t h i n h o l l o w fibres.
Pyrodictium
occultum a n d Pyrodictium brockii are able to g r o w
a u t o t r o p h i c a l l y , g a i n i n g energy b y reduction o f S °
-9
an
an
by H . A l t e r n a t i v e l y , these species are able to
grow m i x o t r o p h i c a l l y o n H a n d thiosulfate i n the
presence o f cell extracts ( T a b l e 4). I n contrast,
Pyrodictium
abyssum is a n obligate heterotroph,
g a i n i n g its energy from a n u p to n o w u n k n o w n
type o f fermentation. E l e m e n t a l sulfur stimulates
g r o w t h , b u t is not essential ( T a b l e 4). A g r o u p o f
coccoid
hyperthermophilic
sulfate-reducing
archaebacteria is represented b y
Archaeglobus
fulgidus [33,36]. It is a facultative a u t o t r o p h . D u r i n g a u t o t r o p h i c growth, Archaeoglobus
fulgidus
gains its energy b y r e d u c t i o n o f thiosulfate b y H
( T a b l e 4). O n l y very little g r o w t h is o b t a i n e d w h e n
thiosulfate is replaced b y sulfate u n d e r autot r o p h i c c o n d i t i o n s . D u r i n g heterotrophic g r o w t h ,
2
2
2
Metabolism of hyperthermophiles
Species
Autotrophic
growth *
Substrates
Electron acceptors
End products
Sulfolobus acidocaldarius
Metallosphaera sedula
Acidianus infernus
f
f
o
S°; H S; cell extracts; sugars
S°; sulfidic ores; cell extracts
S°; sulfidic ores; H
o
o
0 ; S°
H S0 ; ?
H S0 ; ?
H S0 ; H S
Thermoplasma volcanium
_
Yeast extract; cell extracts
0 ; S°
Acetate, C 0 ;
H S; ?
2
2
2
2
2
2
4
2
4
2
4
2
2
2
2
f
Thermoproteus tenax
Pyrobaculum islandicum
f
Pyrobaculum organotrophum
Thermofilum pendens
Pyrodictium occultum
Pyrodictium abyssum
f
Thermodiscus maritimus
Thermococcus celer
Pyrococcus furiosus
b
f
H S
?
Yeast extract; (cell extracts 4- H )
S°; unknown respiration?
H S; ?
Tryptone; yeast extract; casein
Yeast extract; casein; starch;
maltose
H ; formate; lactate; sugars;
proteins
S°; fermentation?
S°; fermentation?
H S; ?
H S; H ; C 0 ; ?
c
co
2
CH
4
C0
2
CH
4
Methanothermus sociabilis
o
H
2
Methanococcus jannaschii
0
H
2
Thermotoga maritima
_
Thermotoga (hermarum
-
Yeast extract; sugars; starch;
cellulose
Yeast extract; (yeast extract +
carbohydrates)
2 _
3
2 -
; cystine
; cystine
2
2
2
2
H S; ?
H S ; acetate;
isovalerate
S°
S°
2
2
2
2
2
3
2
2
2
-
Archaeoglobus fulgidus
S°; ( S 0 - )
Fermentative? ( S ° )
2
-
S;?
S; ?
S;?
S; ?
H ( H +cell extract)
Yeast extract; gelatine; starch;
formate
2
2
-
H
H
H
H
2 -
S°; S 0 "; S O
S°; S ^ - ; S 0
S°; SjO*""; S O
S°
2
-
Desulfurococcus mobilis
Staphylothermus marinus
2
H ; yeast extract; cell extracts
H ; yeast extract; cell extracts
Yeast extract; cell extracts
Yeast extract; tryptone; -f lipid
fraction
Yeast extract; tryptone; casein
Yeast extract; peptone; meat
extract
2
3
SO4 -; S 0 -; S 0
2
2
2
2
2
3
2
2
2
H S ; traces
of C H
2 _
2
3
4
L-Lactate; acetate; H ; C 0
n.d.
Fermentative
2
Fermentative
2
* o * obligately autotrophic; f = facultatively autotrophic; - = heterotrophic.
Autotrophic growth only with S° as electron acceptor.
Autotrophic growth only with S 0 ~ as electron acceptor,
n.d. = not determined.
b
c
2
3
v a r i o u s substrates l i k e lactate, formate,
glucose,
starch
electron
and
proteins
acceptors, sulfate,
can
be
thiosulfate,
used.
As
a n d sulfite c a n
be
s i o n o f factor 420 [36]. D u e to its u n i q u e type o f
RNA
polymerase
Archaeoglobus
used h e t e r o t r o p h i c a l l y . S ° is i n h i b i t o r y d u r i n g a u -
branch
totrophic and heterotrophic growth. In
metabolizers
addition,
situated
traces o f m e t h a n e (up to 0.1 / i m o l / m l ) are f o r m e d
further
via
represented
an
unknown
pathway
[36].
methanogens, cells o f Archaeoglobus
green fluorescence
Similar
to
the
show a blue-
at 420 n m d u e to the posses-
and
forms
16S
the
autotrophic
rRNA
separate
b e t w e e n the
and
by
its
a
sequence,
phylogenetic
thermophilic
sulfur
m e t h a n o g e n s [33,36,37].
marine
Methanococcus
hyperthermophile
jannaschii,
h a d been i s o l a t e d u p to n o w o n l y f r o m
deep sea vents (34). Methanococcus
A
is
which
submarine
jannaschii
is a
strictly a u t o t r o p h i c methanogen
g r o w i n g at tem-
g r o w i n g at temperatures up to 90 ° C ( T a b l e 3;
peratures up to 86 ° C ( T a b l e 3, 4).
[6,39]). T h e y are u s i n g v a r i o u s carbohydrates
T h e marine thermal e n v i r o n m e n t contains also
a variety o f strictly heterotrophic
hyperthermo-
philes. M e m b e r s o f the genus Staphyhthermus
obligate sulfur respirers. C e l l s o f
marinus
as
energy source. A s e n d p r o d u c t s , L-lactate, acetate,
H
and C 0
2
are formed ( T a b l e 4). H y d r o g e n is
2
are
i n h i b i t o r y to growth a n d has to be r e m o v e d d u r i n g
Staphyhthermus
c u l t i v a t i o n . In the presence o f S ° , H S is formed
2
and H
are c o c c o i d a n d grow i n grape-like ag-
2
i n h i b i t i o n is overcome [6].
gregates a n d form giant cells under special n u t r i tional c o n d i t i o n s [30]. C e l l s o f isolates o f the genus
Thermodiscus
dictium,
are disc-shaped. I n contrast to Pyro-
they d o not f o r m fibres, g r o w o n l y up to
4. C O N C L U S I O N S
9 8 ° C and show a m u c h lower G C - c o n t e n t of their
D N A ( T a b l e 3, 4). G r o w t h occurs b y sulfur respir a t i o n o n yeast- a n d cell extracts a n d is stimulated
by H . G o o d
g r o w t h is also obtained
2
without
T h e i s o l a t i o n of various groups of
hyperther-
m o p h i l i c bacteria f r o m geothermally a n d h y d r o thermally heated e n v i r o n m e n t s
demonstrates an
sulfur p o s s i b l y due to an u n k n o w n respiration of
unexpected c o m p l e x i t y of these u p to n o w almost
fermentation. T h e genera Thermococcus
unexplored
and
Pyro-
ecosystems.
Within
these,
primary
coccus are b e l o n g i n g to the T h e r m o c o c c a l e s , w h i c h
p r o d u c t i o n a n d c o n s u m p t i o n o f o r g a n i c matter is
represent up to n o w the deepest branch-off w i t h i n
g o i n g o n at temperatures a r o u n d 100 ° C . T h e en-
the phylogenetic archaebacterial
ergy-yielding reactions of p r i m a r y p r o d u c t i o n is
tree [7,31,32,38].
T h e cells are c o c c o i d shaped ( T a b l e 3).
coccus celer
Thermo-
utilizes tryptone, yeast extract
and
based o n reduction or o x i d a t i o n o f i n o r g a n i c sulfur
compounds by H
2
or 0 , or i n the case o f meth2
protein as c a r b o n sources. G r o w t h is stimulated
anogens o n r e d u c t i o n o f C 0
by sucrose. I n closed culture vessels,
C0
Thermococcus
2
2
by H . Since H ,
2
a n d S ° are formed w i t h i n the
2
environment,
celer grows o p t i m a l l y i n the presence o f sulfur a n d
anaerobic autotrophs u s i n g these c o m p o u n d s
about 1.5 m o l of H S are formed per m o l e of C 0
completely
2
[31]. Thermococcus
2
c a n also grow w i t h o u t sulfur.
independent
of
sunlight.
are
The
con-
sumers of organic matter are most l i k e l y u s i n g cell
U n d e r o p t i m a l c o n d i t i o n s , the generation time of
components
Thermococcus
M o s t of them are g r o w i n g b y sulfur respiration or
furiosus
celer is close to 50 m i n .
Pyrococcus
grows at temperatures up to 1 0 3 ° C a n d
shows a m u c h lower G C content than
Thermococ-
of the d e c a y i n g p r i m a r y
b y u n k n o w n types o f respiration a n d
producers.
fermenta-
tion. A great deal of the a u t o t r o p h s are o p p o r t u n -
cus celer ( T a b l e 3). A t 1 0 0 ° C , the d o u b l i n g time is
istic' heterotrophs, too. T h i s p r o p e r t y m a y be i m -
o n l y 37 m i n [32]. C e l l s o f Pyrococcus
furiosus
portant for effective c o m p e t i t i o n w i t h i n the ex-
highly
polytrichous
motile
flagellation,
due
to
monopolar
are
T h e y grow o n yeast extract, fieptone,
treme environment.
T h e upper
temperature b o r d e r of life is still
casein, starch a n d maltose a n d possess a powerful
u n k n o w n . T h e existence of Pyrodictium
protease a n d amylase. A s m e t a b o l i c products i n
hyperthermophiles
demonstrates that still
unre-
the absence o f sulfur C 0
cognized t h e r m o s t a b i l i z i n g p r i n c i p l e s must
exist.
2
a n d HU were found, the
a n d other
latter b e i n g i n h i b i t o r y to g r o w t h . H y d r o g e n i n -
Since stability of b i o m o l e c u l e s at
h i b i t i o n c a n be prevented b y the a d d i t i o n o f S ° ,
above 100 ° C decreases r a p i d l y [ 4 0 - 4 2 ] , the m a x i -
temperatures
whereupon H S is formed i n a d d i t i o n . T h e m o d e
m a l growth temperature at w h i c h m i c r o b i a l life
of fermentation o f Pyrococcus
2
is still
unclear.
fields c o n t a i n
Many
and
Thermococcus
c a n exist m a y be p o s s i b l y f o u n d between 110 a n d
submarine
hydrothermal
150 ° C . W i t h i n this temperature range, heat-sensi-
also members o f the
genus Thermotoga
eúbacterial
w h i c h are t h r i v i n g together w i t h
h y p e r t h e r m o p h i l i c archaebacteria i n the same env i r o n m e n t . Thermotoga
neapolitana
are
maritima
fermentative
and
tive biomolecules c o u l d p o s s i b l y still be resynthesized
at
biologically
feasible
rates. B e y o n d
interesting questions i n basic research,
the
hyperther-
Thermotoga
mophiles m a y be well suited for the d e v e l o p m e n t
hyperthermophiles
of novel b i o t e c h n o l o g i c a l processes due to their
Torma, A., Eds.), pp. 71-81. Associazione Mineraria
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[13J Huber, G . , Huber, H . and Stetter, K.O. (1986) Isolation
and characterization of new mclal-mobilizing bacteria.
Biotechn. Bioeng. Symp. 16, 239-251.
[14] Huber, G . (1988) Isolierung, Charakterisierung und
ACKNOWLEDGEMENTS
taxonomische Einordnung neuer thermophiler, metallmobilisierender Archaebaklerien. Thesis, University of
W e w o u l d like to thank C h . Stadler for t y p i n g
Regensburg, Regensburg.
the manuscript.
[15] Huber, G., Spinnler, C , Gambacorta, A. and Stetter, K.O.
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