10.3.3.1 Bacteria Domain
In the domain Bacteria, thermophilic representatives belong
to several lineages with some of them having both
mesophilic and thermophilic species. Two lineages located
at the root of the bacterial phylogenetic tree are constituted
by only thermophilic and hyperthermophilic species.
Within the Cyanobacteria, some thermophilic species
were described: the most thermophiles are members of the
genus Chloroflexus and Synechococcus. They are moderate
thermophilic phototrophs and were retrieved from terrestrial
thermal systems.
Within Gram-positive bacteria, numbers of thermophilic
species belonging to the Firmicutes were described; they are
species belonging to the genera Thermoanaerobacterium,
Carboxydibrachium, Caminicella, and Tepidibacter and are
sporulating anaerobes fermentative bacteria.
Also species from the Thermus-Deinococcus group belonging to the genera Thermus, Marinithermus, Rhabdothermus,
Meiothermus, Vulcanithermus, and Oceanithermus were
isolated from both continental or marine hot ecosystems.
They are nonsporulating aerobic (while some of them can
grow under anaerobic conditions) chemoorganotrophs.
More recently, thermophilic species belonging to the
Epsilon division of the Proteobacteria were isolated from
marine hydrothermal ecosystems; they belong to the genera
Caminibacter, Nautilia, and Lebetimonas and are autotrophic anaerobic sulfur reducers. Other bacterial lineages as
Alpha- and Deltaproteobacteria, Bacteroidetes, and
Deferribacteres have some thermophilic members.
Three bacterial lineages located at the root of the bacterial
phylogenetic tree (Aquificales, Desulfurobacteriales, and
Thermodesulfobacteria) are constituted by one or more
genera including only thermophiles and hyperthermophiles.
Species of the genera Thermodesulfobacterium and
Thermodesulfatator are thermophilic sulfate reducers (optimal temperature around 70
C) while the newly described
species Thermosulfurimonas dismutans mediate elemental
sulfur disproportionation. They are autotrophs and form a
separate lineage between Aquificales and Thermotogales.
Microorganisms from the genera Aquifex, Persephonella
and Desulfurobacterium, Balnearium, and Thermovibrio
are chemolithotrophs. Some species from the Aquificales
use H 2 as electron donor (hydrogenotrophic species) but
can also use S
or S 2 O 3 and O 2 and NO 3 as electron
acceptors; they can grow at temperatures up to 95
C and
tolerate only low dioxygen concentration; they are (with
some archaeal species) the rare known aerobic (more specifically microaerophilic) hyperthermophiles.
Thermocrinis ruber is an organism closely related to
Aquifex that grows in the outflow from some hot spring
from Yellowstone National Park. It forms pink streamers
consisting of a filamentous form of the cells attached to
siliceous sinter. This hyperthermophilic organism (optimal
growth at 80
C) is chemolithotroph being able to oxidize
H 2 , S
, or thiosulfate with O 2 as terminal electron acceptor.
The Thermotogales that also deeply branched in the bacterial phylogenetic tree include more than 20 species
isolated from a great diversity of hot ecosystems. First
described as being composed only by thermophilic species,
this order was recently shown to include mesophilic species
of the genera Mesotoga (Ben Hania et al. 2011). Some
Thermotoga and related species are thermophilic fermentative chemoorganotrophic bacteria; their optimal temperature
for growth is between 60 and 80
C. They were isolated from
terrestrial hot spring (Thermotoga, Fervidobacterium) as
well as from either coastal or deep marine hot springs
(Thermotoga, Thermosipho, Marinitoga) but also from
petroleum reservoirs (Geotoga, Petrotoga). They have in
common the unique characteristic of having an extern
sheet-like envelope called the “Toga” (Fig. 6.10e).
10.3.3.2 Archaea Domain
Numerous thermophilic and hyperthermophilic species
belong to the two main branches of the archaeal domain:
the Euryarchaeota and the Crenarchaeota (Fig. 10.7).
These two lineages also include nonthermophilic species
as extremes halophiles, mesophilic methanogens
(Euryarchaeota), and species mainly uncultivated today
belonging to the Crenarchaeota and the newly described
domain Thaumarchaeota (Brochier-Armanet et al. 2008).
Within the Crenarchaeota, hyperthermophilic species
cluster at the basis of the tree and gather a majority of
organisms that are mainly chemolithotrophs, autotrophs,
and some chemoorganotrophs. Euryarchaeota gather
hyperthermophiles as diverse as the methane-producing
methanoarchaea and chemoorganotrophic species.
10.3.3.3 Hyperthermophilic Euryarchaeota
Most of hyperthermophilic methanoarchaea (methanogenic
species) belong to the order Methanococcales which
includes four hydrogenotrophic genera Methanococcus,
Methanocaldococcus,
Methanothermococcus,
and
Methanotorris. These species were isolated from both submarine and terrestrial hydrothermal systems. Species
belonging to the Methanosarcinales, which are acetoclastic
species, were also described. While not being isolated yet,
thermophilic anaerobic methane oxidation (AOM) mediated
by ANME Methanoarchaea was reported from hot environment (Biddle et al. 2012).
Methanopyrus kandleri has a specific phylogenetic position far from other methanoarchaea and is a
hydrogenotrophic methanogen isolated from hydrothermal
chimneys and sediments. This species exhibits rapid growth
rate at 100
C and is the most thermophilic described
methanogen (up to 110
C) so far.
364
J.-L. Cayol et al.
In the domain Bacteria, thermophilic representatives belong
to several lineages with some of them having both
mesophilic and thermophilic species. Two lineages located
at the root of the bacterial phylogenetic tree are constituted
by only thermophilic and hyperthermophilic species.
Within the Cyanobacteria, some thermophilic species
were described: the most thermophiles are members of the
genus Chloroflexus and Synechococcus. They are moderate
thermophilic phototrophs and were retrieved from terrestrial
thermal systems.
Within Gram-positive bacteria, numbers of thermophilic
species belonging to the Firmicutes were described; they are
species belonging to the genera Thermoanaerobacterium,
Carboxydibrachium, Caminicella, and Tepidibacter and are
sporulating anaerobes fermentative bacteria.
Also species from the Thermus-Deinococcus group belonging to the genera Thermus, Marinithermus, Rhabdothermus,
Meiothermus, Vulcanithermus, and Oceanithermus were
isolated from both continental or marine hot ecosystems.
They are nonsporulating aerobic (while some of them can
grow under anaerobic conditions) chemoorganotrophs.
More recently, thermophilic species belonging to the
Epsilon division of the Proteobacteria were isolated from
marine hydrothermal ecosystems; they belong to the genera
Caminibacter, Nautilia, and Lebetimonas and are autotrophic anaerobic sulfur reducers. Other bacterial lineages as
Alpha- and Deltaproteobacteria, Bacteroidetes, and
Deferribacteres have some thermophilic members.
Three bacterial lineages located at the root of the bacterial
phylogenetic tree (Aquificales, Desulfurobacteriales, and
Thermodesulfobacteria) are constituted by one or more
genera including only thermophiles and hyperthermophiles.
Species of the genera Thermodesulfobacterium and
Thermodesulfatator are thermophilic sulfate reducers (optimal temperature around 70
C) while the newly described
species Thermosulfurimonas dismutans mediate elemental
sulfur disproportionation. They are autotrophs and form a
separate lineage between Aquificales and Thermotogales.
Microorganisms from the genera Aquifex, Persephonella
and Desulfurobacterium, Balnearium, and Thermovibrio
are chemolithotrophs. Some species from the Aquificales
use H 2 as electron donor (hydrogenotrophic species) but
can also use S
or S 2 O 3 and O 2 and NO 3 as electron
acceptors; they can grow at temperatures up to 95
C and
tolerate only low dioxygen concentration; they are (with
some archaeal species) the rare known aerobic (more specifically microaerophilic) hyperthermophiles.
Thermocrinis ruber is an organism closely related to
Aquifex that grows in the outflow from some hot spring
from Yellowstone National Park. It forms pink streamers
consisting of a filamentous form of the cells attached to
siliceous sinter. This hyperthermophilic organism (optimal
growth at 80
C) is chemolithotroph being able to oxidize
H 2 , S
, or thiosulfate with O 2 as terminal electron acceptor.
The Thermotogales that also deeply branched in the bacterial phylogenetic tree include more than 20 species
isolated from a great diversity of hot ecosystems. First
described as being composed only by thermophilic species,
this order was recently shown to include mesophilic species
of the genera Mesotoga (Ben Hania et al. 2011). Some
Thermotoga and related species are thermophilic fermentative chemoorganotrophic bacteria; their optimal temperature
for growth is between 60 and 80
C. They were isolated from
terrestrial hot spring (Thermotoga, Fervidobacterium) as
well as from either coastal or deep marine hot springs
(Thermotoga, Thermosipho, Marinitoga) but also from
petroleum reservoirs (Geotoga, Petrotoga). They have in
common the unique characteristic of having an extern
sheet-like envelope called the “Toga” (Fig. 6.10e).
10.3.3.2 Archaea Domain
Numerous thermophilic and hyperthermophilic species
belong to the two main branches of the archaeal domain:
the Euryarchaeota and the Crenarchaeota (Fig. 10.7).
These two lineages also include nonthermophilic species
as extremes halophiles, mesophilic methanogens
(Euryarchaeota), and species mainly uncultivated today
belonging to the Crenarchaeota and the newly described
domain Thaumarchaeota (Brochier-Armanet et al. 2008).
Within the Crenarchaeota, hyperthermophilic species
cluster at the basis of the tree and gather a majority of
organisms that are mainly chemolithotrophs, autotrophs,
and some chemoorganotrophs. Euryarchaeota gather
hyperthermophiles as diverse as the methane-producing
methanoarchaea and chemoorganotrophic species.
10.3.3.3 Hyperthermophilic Euryarchaeota
Most of hyperthermophilic methanoarchaea (methanogenic
species) belong to the order Methanococcales which
includes four hydrogenotrophic genera Methanococcus,
Methanocaldococcus,
Methanothermococcus,
and
Methanotorris. These species were isolated from both submarine and terrestrial hydrothermal systems. Species
belonging to the Methanosarcinales, which are acetoclastic
species, were also described. While not being isolated yet,
thermophilic anaerobic methane oxidation (AOM) mediated
by ANME Methanoarchaea was reported from hot environment (Biddle et al. 2012).
Methanopyrus kandleri has a specific phylogenetic position far from other methanoarchaea and is a
hydrogenotrophic methanogen isolated from hydrothermal
chimneys and sediments. This species exhibits rapid growth
rate at 100
C and is the most thermophilic described
methanogen (up to 110
C) so far.
364
J.-L. Cayol et al.