1 Introduction
Enzymes catalyze reactions with great specificity and rate enhancements. These
catalytic properties, together with their environmentally benign and easy disposal
nature, provide tremendous opportunities for industries. Often, industrial applications demand extreme conditions like high or low pH, elevated temperature, high
solvent concentration, etc. On the other hand, nature provides, with some notable
exceptions, enzymes that operate best under rather mild conditions. In industrial
processes, the use of robust enzymes that directly mediate the catalysis without any
pre-adjustment(s) such as cooling and neutralization has enormous economic and
technical advantages over the use of enzymes which are labile to the industrial
application conditions. Thus, there has always been interest in finding enzymes
that are compatible with industrial application conditions. This impetus forged
with the basic research interest geared for the exploration of life that can serve as
sources of enzymes that are amenable to industrial applications. The major search
target for such robust enzymes has been extremophiles, organisms that thrive in
extreme environments. The assumption is that those who dwell in extreme habitats
evolved enzymes that are operationally stable in the extreme environments in which
they are thriving. Thus, it seems ideal to look for thermostable enzymes from thermophiles, acid active enzymes from acidophiles, alkaline active enzymes from alkaliphiles,
cold active enzymes from psychrophiles, and so on. Indeed, it has been proven that
extremophiles produce fascinating enzymes which are able to mediate reactions under
extreme conditions at which biocatalysts from their mesophilic counterparts are often
neither active nor stable. Over the years, a range of enzymes has been reported from
extremophiles. Characterization studies of these enzymes revealed the suitability of
some of these enzymes in industrial applications. The discovery of industrially amenable enzymes of extremophiles not only substitutes some of the toxic and hazardous
industrial processes but also paved the way to envision new industrial processes. This
has significantly contributed to the expansion of industrial biocatalysis.
Plant biomass modifying enzymes are among the extremozymes that attracted
a great deal of interest from researchers, industrialists, and environmentalists.
Enzymes which act on various constituents of plant biomass have got applications
such as in food, pulp, detergent, textile, and bioethanol industries [1–4]. In addition,
there is a recent global trend toward greener and sustainable processes which is
driven by the growing concern of economic, environmental, and health issues related
to heavy use of petroleum and its derivatives [5, 6]. Huge amount of lignocellulosic
materials is generated from agricultural and agroindustry processes each year. This
biomass can potentially serve as renewable feedstock to produce chemicals, materials, and energy carriers that may be of substitute to petroleum and its derivatives
[7–9]. The valorization of the biomass to these entities involves hydrolysis which
can be done either by chemical or biotechnological approaches. However, the
biotechnological route is preferable due to its greener, clean, specific, and benign
nature. Moreover, it is free from undesirable products such as fermentation inhibitors. Thus, the robust extremozymes can be instrumental in valorization of plant
biomass to various products. In this regard, the emergence and expansion of the
248
G. Mamo
Enzymes catalyze reactions with great specificity and rate enhancements. These
catalytic properties, together with their environmentally benign and easy disposal
nature, provide tremendous opportunities for industries. Often, industrial applications demand extreme conditions like high or low pH, elevated temperature, high
solvent concentration, etc. On the other hand, nature provides, with some notable
exceptions, enzymes that operate best under rather mild conditions. In industrial
processes, the use of robust enzymes that directly mediate the catalysis without any
pre-adjustment(s) such as cooling and neutralization has enormous economic and
technical advantages over the use of enzymes which are labile to the industrial
application conditions. Thus, there has always been interest in finding enzymes
that are compatible with industrial application conditions. This impetus forged
with the basic research interest geared for the exploration of life that can serve as
sources of enzymes that are amenable to industrial applications. The major search
target for such robust enzymes has been extremophiles, organisms that thrive in
extreme environments. The assumption is that those who dwell in extreme habitats
evolved enzymes that are operationally stable in the extreme environments in which
they are thriving. Thus, it seems ideal to look for thermostable enzymes from thermophiles, acid active enzymes from acidophiles, alkaline active enzymes from alkaliphiles,
cold active enzymes from psychrophiles, and so on. Indeed, it has been proven that
extremophiles produce fascinating enzymes which are able to mediate reactions under
extreme conditions at which biocatalysts from their mesophilic counterparts are often
neither active nor stable. Over the years, a range of enzymes has been reported from
extremophiles. Characterization studies of these enzymes revealed the suitability of
some of these enzymes in industrial applications. The discovery of industrially amenable enzymes of extremophiles not only substitutes some of the toxic and hazardous
industrial processes but also paved the way to envision new industrial processes. This
has significantly contributed to the expansion of industrial biocatalysis.
Plant biomass modifying enzymes are among the extremozymes that attracted
a great deal of interest from researchers, industrialists, and environmentalists.
Enzymes which act on various constituents of plant biomass have got applications
such as in food, pulp, detergent, textile, and bioethanol industries [1–4]. In addition,
there is a recent global trend toward greener and sustainable processes which is
driven by the growing concern of economic, environmental, and health issues related
to heavy use of petroleum and its derivatives [5, 6]. Huge amount of lignocellulosic
materials is generated from agricultural and agroindustry processes each year. This
biomass can potentially serve as renewable feedstock to produce chemicals, materials, and energy carriers that may be of substitute to petroleum and its derivatives
[7–9]. The valorization of the biomass to these entities involves hydrolysis which
can be done either by chemical or biotechnological approaches. However, the
biotechnological route is preferable due to its greener, clean, specific, and benign
nature. Moreover, it is free from undesirable products such as fermentation inhibitors. Thus, the robust extremozymes can be instrumental in valorization of plant
biomass to various products. In this regard, the emergence and expansion of the
248
G. Mamo