12.3 Extremophiles in Extreme Environments
Extremophiles include members of all three domains of life—bacteria, archaea and
eukarya. Most of the extremophilic microorganisms are archaea, but this group also
includes eukaryotes such as protists (algae, fungi and protozoa) and multicellular
organisms. Culture-dependent and culture-independent (molecular) methods have
been employed for understanding the diversity of microbes in extreme environments. Archaea is the main group to thrive in extreme environments. They are quite
skilled in adapting to different extreme conditions. Most of acidophilic, halophilic
and hyperthermophillic microorganisms belong to the archaea group. These organisms have evolved several structural and chemical adaptations, which allow them to
survive and grow in extreme environments (Satyanarayana et al. 2005). Among
bacteria, cyanobacteria is the best adapted group to various extreme conditions such
as formation of microbial mats with other bacteria from Antarctic ice to continental
hot springs. Among eukaryotes, fungi are the most versatile and ecological successful phylogenetic lineage. The phylogenetic diversity of extremophiles is high and
very complex to study. Some extremophiles are adapted to the same extreme
conditions, even though dispersed broadly in the phylogenetic tree of life. Some
genera or orders contain only extremophiles, whereas other genera or orders contain
both mesophiles and extremophiles.
Specific biological functions and metabolic processes of these microorganisms
are mediated by proteins and enzymes known as extremozymes which are responsible for unusual properties of extremophiles. Extremophiles are capable of surviving in extreme environments due to extremozymes having unique feature because of
extreme thermal stability and resistance against chemical denaturants such as detergents, chaotropic agents, organic solvents and extreme of pH (Gaur et al. 2010;
Karan et al. 2011). The discovery of new extremophilic microorganisms and their
extremozymes has a great impact on the field of biocatalysis and hold tremendous
potential as industrial biocatalysts to work under harsh conditions.
The extreme environments are so unique that the organisms are highly specialized
with specific protein adaptations such as chaperone systems or enzymes
(extremozymes) capable of functioning in the environment without denaturing.
These enzymes or proteins are capable of functioning under such conditions in
which mesophilic proteins or enzymes may not work. Extremophiles have found
use as part of bioremediation of contaminated environments due to their unique
metabolic activities and tolerance to certain conditions. A number of proteins or
extremozymes sourced from extremophiles have already been utilized in industry for
the purpose as diverse as molecular biology reagents or as common place as laundry
detergents. The removal and detoxification of contaminants and wastes can be
achieved by means of extremozymes such as oxidoreductase (da Fonseca et al.
2015), laccase (Fang et al. 2012), dioxygenase (Saito et al. 2000), alkane hydroxylase (Wang et al. 2010b), haloalkane dehalogenase (Zhang et al. 2013; Nikolaivits
et al. 2017). Usefulness of extremophiles in various industrial and other applications
such as bioremediation is due to their wide spectrum of unique properties such as
stability to elevated temperature, extremes pH, organic solvents and high ionic
12 Potential of Extremophiles for Bioremediation
301
Extremophiles include members of all three domains of life—bacteria, archaea and
eukarya. Most of the extremophilic microorganisms are archaea, but this group also
includes eukaryotes such as protists (algae, fungi and protozoa) and multicellular
organisms. Culture-dependent and culture-independent (molecular) methods have
been employed for understanding the diversity of microbes in extreme environments. Archaea is the main group to thrive in extreme environments. They are quite
skilled in adapting to different extreme conditions. Most of acidophilic, halophilic
and hyperthermophillic microorganisms belong to the archaea group. These organisms have evolved several structural and chemical adaptations, which allow them to
survive and grow in extreme environments (Satyanarayana et al. 2005). Among
bacteria, cyanobacteria is the best adapted group to various extreme conditions such
as formation of microbial mats with other bacteria from Antarctic ice to continental
hot springs. Among eukaryotes, fungi are the most versatile and ecological successful phylogenetic lineage. The phylogenetic diversity of extremophiles is high and
very complex to study. Some extremophiles are adapted to the same extreme
conditions, even though dispersed broadly in the phylogenetic tree of life. Some
genera or orders contain only extremophiles, whereas other genera or orders contain
both mesophiles and extremophiles.
Specific biological functions and metabolic processes of these microorganisms
are mediated by proteins and enzymes known as extremozymes which are responsible for unusual properties of extremophiles. Extremophiles are capable of surviving in extreme environments due to extremozymes having unique feature because of
extreme thermal stability and resistance against chemical denaturants such as detergents, chaotropic agents, organic solvents and extreme of pH (Gaur et al. 2010;
Karan et al. 2011). The discovery of new extremophilic microorganisms and their
extremozymes has a great impact on the field of biocatalysis and hold tremendous
potential as industrial biocatalysts to work under harsh conditions.
The extreme environments are so unique that the organisms are highly specialized
with specific protein adaptations such as chaperone systems or enzymes
(extremozymes) capable of functioning in the environment without denaturing.
These enzymes or proteins are capable of functioning under such conditions in
which mesophilic proteins or enzymes may not work. Extremophiles have found
use as part of bioremediation of contaminated environments due to their unique
metabolic activities and tolerance to certain conditions. A number of proteins or
extremozymes sourced from extremophiles have already been utilized in industry for
the purpose as diverse as molecular biology reagents or as common place as laundry
detergents. The removal and detoxification of contaminants and wastes can be
achieved by means of extremozymes such as oxidoreductase (da Fonseca et al.
2015), laccase (Fang et al. 2012), dioxygenase (Saito et al. 2000), alkane hydroxylase (Wang et al. 2010b), haloalkane dehalogenase (Zhang et al. 2013; Nikolaivits
et al. 2017). Usefulness of extremophiles in various industrial and other applications
such as bioremediation is due to their wide spectrum of unique properties such as
stability to elevated temperature, extremes pH, organic solvents and high ionic
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301