into cells by co-transportation with other substrates. In Na
+
-
dependent transport systems, protons are exchanged with Na
+
by an H
+
/Na
+ antiporter, generating a sodium-motive force
which transports the substrates with Na
+ ions into the cells.
The specific requirement of alkaliphilic bacteria for Na
+ is
dependant of an efficient pathway of Na
+ ions reintroduction
into the cell, thus allowing the antiporter to operate. At least
two mechanisms are important, the Na
+
/solute symporters and
the sodium channels. The precise functioning of these processes remains an interesting aspect of the work to be
conducted with alkaliphilic bacteria (cf. Sect. 9.6.3).
10.7.5 Biotechnological Applications of
Alkaliphiles
Microbial communities of natural environments such as alkaline soda lakes have for a long time attracted the attention of
industry because of the many possible uses of their enzymes
or metabolites in industrial processes (Horikoshi 2011).
Alkaliphiles have a great commercial interest in the production of enzymes such as alkaline proteases commonly used in
biological washing powders and in the leather industry. Starch
industry uses alkaline cyclodextrin glycotransferases in order
to obtain cyclodextrins from starch for use in the cosmetics,
pharmacology, chemistry, and food industry. Alkaline
amylases and xylanases have also many applications in the
paper industry. Studies of alkaline enzymes mainly focused
on the most commonly observed microorganisms in natural
environments for which isolation is easy. So, many
alkaliphilic Bacillus species have been isolated through the
work of Horikoshi (2011).
The biotechnological potential of some archaea in particular was also evaluated as they contain lipids with a
stereochemical configuration very different from that of
bacteria. The archaeal haloalkaliphilic Natronococcus
strain Ah-36 synthesizes an extracellular amylase which
allows the production of maltotriose. The gene for this
enzyme was cloned and expressed in Haloferax volcanii.
The majority of haloalkaliphiles contain pigments involved
in the translocation of ions across the cell membrane.
Bacteriorhodopsin, as a light-driven proton pump, and the
halorhodopsin, as a pump of chlorides for entering the cell,
open large biotechnological perspectives. They may be
used in diverse applications such as holography and information storage. The production of Spirulina biomass as a
source of proteins is still used in Africa and in other parts of
the world. The European Space Agency is considering its
use for organic matter recycling in long-duration space
flights.
Despite harsh settled conditions existing (extreme pH
values, most often coupled to high salinity), in soda lakes,
these environments are inhabited by a wide range of
microorganisms that include the major phylogenetic and
trophic groups of bacteria and archaea including fermentative, nitrate- and sulfate-reducing bacteria, methanoarchaea,
and haloarchaea. The functioning of basic carbon, nitrogen,
and sulfur cycles is particularly active in soda lakes. Although
alkaline environments have been intensively studied during
the last years, microbial diversity and community structure
that develop and the role played by some alkaliphiles are not
fully understood. Subsequently our knowledge of the distribution and taxonomic diversity of such extremophiles will
undoubtedly improve, thanks to the help of (1) microbiologists
with isolation and characterization of novel microorganisms
and (2) genome sequencing programs and total DNA
sequencing directly from alkaliphilic environment.
10.8 Conclusion
10.8.1 Extremophiles and Exobiology
The term “exobiology” (now astrobiology for Englishspeaking authors) was first used by the Nobel Prize winner
Joshua Lederberf to name the science devoted with life, its
origin, evolution, and distribution in the universe. Such a
topic probably exists (although unnamed) since the beginning of humanity. This topic is very complex because those
who study it (human beings) have no reference on life for
comparison, with the exception of their own references as
inhabitants of Earth.
There is no doubt that planet Earth, formed by accretion
more than 4.5 billion years ago, was more hostile at its
origin, than today. Particularly, temperature was too much
more elevated to keep water liquid. Now, liquid water is
obligatory required for life (such as we know). 100–200 million years later, liquid water existed on Earth, temperature
was still rather high, volcanism was very active, and huge
meteorites frequently hit the surface of Earth (the impact of
an object with about the size of Mars was at the origin of the
Moon) up to 3.8 billion years ago.
One billion years after accretion, it seems that life had
arose, as suggested by analysis of ancients rocks where
fossils assigned to ancient life forms, presumably anaerobes,
were reported. About one billion years later, dioxygen is
present in the atmosphere; one billion years more and the
first Eukaryotes appeared (cf. Chap. 4).
The discovery of extremophiles and particularly the
hyperthermophiles has deeply changed our vision of life on
Earth. Life is not only installed in environments suitable for
human beings, animals, and plants: life abounds (essentially
via microscopic and prokaryotic forms) in places of Earth
where humans cannot venture without a protection or using
complex technologies.
10 The Extreme Conditions of Life on the Planet and Exobiology
391
+
-
dependent transport systems, protons are exchanged with Na
+
by an H
+
/Na
+ antiporter, generating a sodium-motive force
which transports the substrates with Na
+ ions into the cells.
The specific requirement of alkaliphilic bacteria for Na
+ is
dependant of an efficient pathway of Na
+ ions reintroduction
into the cell, thus allowing the antiporter to operate. At least
two mechanisms are important, the Na
+
/solute symporters and
the sodium channels. The precise functioning of these processes remains an interesting aspect of the work to be
conducted with alkaliphilic bacteria (cf. Sect. 9.6.3).
10.7.5 Biotechnological Applications of
Alkaliphiles
Microbial communities of natural environments such as alkaline soda lakes have for a long time attracted the attention of
industry because of the many possible uses of their enzymes
or metabolites in industrial processes (Horikoshi 2011).
Alkaliphiles have a great commercial interest in the production of enzymes such as alkaline proteases commonly used in
biological washing powders and in the leather industry. Starch
industry uses alkaline cyclodextrin glycotransferases in order
to obtain cyclodextrins from starch for use in the cosmetics,
pharmacology, chemistry, and food industry. Alkaline
amylases and xylanases have also many applications in the
paper industry. Studies of alkaline enzymes mainly focused
on the most commonly observed microorganisms in natural
environments for which isolation is easy. So, many
alkaliphilic Bacillus species have been isolated through the
work of Horikoshi (2011).
The biotechnological potential of some archaea in particular was also evaluated as they contain lipids with a
stereochemical configuration very different from that of
bacteria. The archaeal haloalkaliphilic Natronococcus
strain Ah-36 synthesizes an extracellular amylase which
allows the production of maltotriose. The gene for this
enzyme was cloned and expressed in Haloferax volcanii.
The majority of haloalkaliphiles contain pigments involved
in the translocation of ions across the cell membrane.
Bacteriorhodopsin, as a light-driven proton pump, and the
halorhodopsin, as a pump of chlorides for entering the cell,
open large biotechnological perspectives. They may be
used in diverse applications such as holography and information storage. The production of Spirulina biomass as a
source of proteins is still used in Africa and in other parts of
the world. The European Space Agency is considering its
use for organic matter recycling in long-duration space
flights.
Despite harsh settled conditions existing (extreme pH
values, most often coupled to high salinity), in soda lakes,
these environments are inhabited by a wide range of
microorganisms that include the major phylogenetic and
trophic groups of bacteria and archaea including fermentative, nitrate- and sulfate-reducing bacteria, methanoarchaea,
and haloarchaea. The functioning of basic carbon, nitrogen,
and sulfur cycles is particularly active in soda lakes. Although
alkaline environments have been intensively studied during
the last years, microbial diversity and community structure
that develop and the role played by some alkaliphiles are not
fully understood. Subsequently our knowledge of the distribution and taxonomic diversity of such extremophiles will
undoubtedly improve, thanks to the help of (1) microbiologists
with isolation and characterization of novel microorganisms
and (2) genome sequencing programs and total DNA
sequencing directly from alkaliphilic environment.
10.8 Conclusion
10.8.1 Extremophiles and Exobiology
The term “exobiology” (now astrobiology for Englishspeaking authors) was first used by the Nobel Prize winner
Joshua Lederberf to name the science devoted with life, its
origin, evolution, and distribution in the universe. Such a
topic probably exists (although unnamed) since the beginning of humanity. This topic is very complex because those
who study it (human beings) have no reference on life for
comparison, with the exception of their own references as
inhabitants of Earth.
There is no doubt that planet Earth, formed by accretion
more than 4.5 billion years ago, was more hostile at its
origin, than today. Particularly, temperature was too much
more elevated to keep water liquid. Now, liquid water is
obligatory required for life (such as we know). 100–200 million years later, liquid water existed on Earth, temperature
was still rather high, volcanism was very active, and huge
meteorites frequently hit the surface of Earth (the impact of
an object with about the size of Mars was at the origin of the
Moon) up to 3.8 billion years ago.
One billion years after accretion, it seems that life had
arose, as suggested by analysis of ancients rocks where
fossils assigned to ancient life forms, presumably anaerobes,
were reported. About one billion years later, dioxygen is
present in the atmosphere; one billion years more and the
first Eukaryotes appeared (cf. Chap. 4).
The discovery of extremophiles and particularly the
hyperthermophiles has deeply changed our vision of life on
Earth. Life is not only installed in environments suitable for
human beings, animals, and plants: life abounds (essentially
via microscopic and prokaryotic forms) in places of Earth
where humans cannot venture without a protection or using
complex technologies.
10 The Extreme Conditions of Life on the Planet and Exobiology
391