environments which once have been considered too extreme to host life are found
inhabited by richly diverse group of organisms. The discovery of these organisms
dwelling in extreme environments not only heralds a new dawn in biotechnology but
also brought a substantial change in human perception regarding the limits of
habitable environments. Although the limits of extreme conditions at which organisms can survive and thrive are not exactly known, the results of these studies
support the notion that no matter what the condition may be, there could be life at
least where there is liquid water. Indeed, this contributed to the dramatic expansion
of human knowledge on adaptability of life, which flourishes from environments of
frozen water of around À20
C [8] to hydrothermal vents which are above 120
C [9],
and in extreme pH values as low as pH 0 [6] and as high as pH 13.5 [4], and in many
other extreme conditions such as high salinity, high level of radiation, and high
pressure [10]. The organisms adapted to these extreme environments are often
referred to as extremophiles and are known to have immense biotechnological
application potentials.
2 Extremophiles
Extremophiles are organisms evolved to exist in a variety of extreme environments
which could be natural, manmade, temporary, or permanent. Extreme environments
are ubiquitous and differ according to their characterizing condition(s) such as
acidic, alkaline, cold, or saline. The organisms adapted to these habitats also vary
as the nature of the extreme condition. Thus, the categorization of these organisms in
one group, extremophiles, is just for simplicity but does not reflect any biological
commonality. As shown in Table 1, extremophiles are named according to the nature
of their habitats or conditions that they are adapted to and fall into several classes.
Taxonomical studies on organisms dwelling in extreme habitats revealed that
extremophiles are diverse, and the great majority belongs to the domains of Archaea
and Eubacteria [11–14]. However, a variety of unicellular and multicellular eukaryotic organisms have also been reported [15–17].
Extremophiles evolved ingenious structural and functional adaptations which
allow them not only to survive but also thrive in their specific extreme environments.
These adaptations are of great importance in biotechnology and can be harnessed for
various applications (Fig. 1).
The use of enzymes in industrial processes has many advantages including
shorter processing time, low energy consumption, process cost minimization, safe
to use, high selectivity, and environmentally friendly [18]. However, most industrial
processes involve harsh conditions which are tough for most enzymes to cope with.
Thus, there has always been the interest for robust enzymes that are amenable to
industrial conditions. Extremophiles are proven sources of fascinating enzymes
(which are also known as extremozymes) that function under extreme conditions
in which biocatalysts from their mesophilic counterparts could neither be active nor
stable. Due to their desirable properties, several extremozymes have made their ways
into various industrial processes (Table 2).
Alkaliphiles: The Versatile Tools in Biotechnology
5
inhabited by richly diverse group of organisms. The discovery of these organisms
dwelling in extreme environments not only heralds a new dawn in biotechnology but
also brought a substantial change in human perception regarding the limits of
habitable environments. Although the limits of extreme conditions at which organisms can survive and thrive are not exactly known, the results of these studies
support the notion that no matter what the condition may be, there could be life at
least where there is liquid water. Indeed, this contributed to the dramatic expansion
of human knowledge on adaptability of life, which flourishes from environments of
frozen water of around À20
C [8] to hydrothermal vents which are above 120
C [9],
and in extreme pH values as low as pH 0 [6] and as high as pH 13.5 [4], and in many
other extreme conditions such as high salinity, high level of radiation, and high
pressure [10]. The organisms adapted to these extreme environments are often
referred to as extremophiles and are known to have immense biotechnological
application potentials.
2 Extremophiles
Extremophiles are organisms evolved to exist in a variety of extreme environments
which could be natural, manmade, temporary, or permanent. Extreme environments
are ubiquitous and differ according to their characterizing condition(s) such as
acidic, alkaline, cold, or saline. The organisms adapted to these habitats also vary
as the nature of the extreme condition. Thus, the categorization of these organisms in
one group, extremophiles, is just for simplicity but does not reflect any biological
commonality. As shown in Table 1, extremophiles are named according to the nature
of their habitats or conditions that they are adapted to and fall into several classes.
Taxonomical studies on organisms dwelling in extreme habitats revealed that
extremophiles are diverse, and the great majority belongs to the domains of Archaea
and Eubacteria [11–14]. However, a variety of unicellular and multicellular eukaryotic organisms have also been reported [15–17].
Extremophiles evolved ingenious structural and functional adaptations which
allow them not only to survive but also thrive in their specific extreme environments.
These adaptations are of great importance in biotechnology and can be harnessed for
various applications (Fig. 1).
The use of enzymes in industrial processes has many advantages including
shorter processing time, low energy consumption, process cost minimization, safe
to use, high selectivity, and environmentally friendly [18]. However, most industrial
processes involve harsh conditions which are tough for most enzymes to cope with.
Thus, there has always been the interest for robust enzymes that are amenable to
industrial conditions. Extremophiles are proven sources of fascinating enzymes
(which are also known as extremozymes) that function under extreme conditions
in which biocatalysts from their mesophilic counterparts could neither be active nor
stable. Due to their desirable properties, several extremozymes have made their ways
into various industrial processes (Table 2).
Alkaliphiles: The Versatile Tools in Biotechnology
5