31-07-2013, 04:20 PM
Microbial cellulases Production, applications and challenges
[attachment=56890]
ABSTRACT
Microbial cellulases find applications in various industries and constitute a major group of the industrial enzymes.
Recently, there is resurgence in utilization of biomass for fuel production employing cellulases and hence forth in obtaining
better yields and novel activities. Improving the economics of such processes will involve cost reduction in cellulase
production which may be achieved by better bioprocesses and genetic improvement of cellulase producers to yield more of
the enzyme. The review discusses the current knowledge on cellulase production by microorganisms and the genetic
controls exercised on it. It discusses the industrial applications of cellulases and the challenges in cellulase research
especially in the direction of improving the process economics of enzyme production.
Introduction
Cellulose is the most common organic polymer,
representing about 1.5 × 1012 tons of the total annual
biomass production through photosynthesis especially
in the tropics, and is considered to be an almost
inexhaustible source of raw material for different
products1. It is the most abundant and renewable
biopolymer on earth and the dominating waste
material from agriculture2. A promising strategy for
efficient utilization of this renewable resource is the
microbial hydrolysis of lignocellulosic waste and
fermentation of the resultant reducing sugars for
production of desired metabolites or biofuel.
Microorganisms producing Cellulases
Cellulolytic microbes are primarily carbohydrate
degraders and are generally unable to use proteins or
lipids as energy sources for growth8. Cellulolytic
microbes notably the bacteria Cellulomonas and
Cytophaga and most fungi can utilize a variety of
other carbohydrates in addition to cellulose31-32, while
the anaerobic celluloytic species have a restricted
carbohydrate range, limited to cellulose and or its
hydrolytic products33-34. The ability to secrete large
amounts of extracellular protein is characteristic of
certain fungi and such strains are most suited for
production of higher levels of extracellular cellulases.
One of the most extensively studied fungi is
Trichoderma reesei, which converts native as well as
derived cellulose to glucose. Most commonly studied
cellulolytic organisms include: Fungal species-
Trichoderma, Humicola, Penicillium, Aspergillus;
Bacteria-Bacilli, Pseudomonads, Cellulomonas; and
Actinomycetes-Streptomyces, Actinomucor, and
Streptomyces.
Applications of Cellulases
Cellulases were initially investigated several
decades back for the bioconversion of biomass which
gave way to research in the industrial applications of
the enzyme in animal feed, food, textiles and
detergents and in the paper industry123. With the
shortage of fossil fuels and the arising need to find
alternative source for renewable energy and fuels,
there is a renewal of interest in the bioconversion of
lignocellulosic biomass using cellulases and other
enzymes. In the other fields, however, the
technologies and products using cellulases have
reached the stage where these enzymes have become
indispensable.
Concluding Remarks
The biological aspects of processing of cellulosic
biomass become the crux of future researches
involving cellulases and cellulolytic microorganisms.
The problems which warrants attention is not limited
to cellulase production alone, but a concerted effort in
understanding the basic physiology of cellulolytic
microbes and the utilization of this knowledge
coupled with engineering principles to achieve a
better processing and utilization of this most abundant
natural resource. The aspects open to consideration
include technologies for pre-treatment of cellulosic
materials for a better microbial attack, processes for
cost effective production of cellulases, treatment of
biomass for production of hydrolytic products, which
can then serve as substrates for downstream
fermentative production of valuable metabolites,
organism development by metabolic engineering, and
finally protein engineering to improve the properties
of enzymes to increase their specific activities,
process tolerance and stability.
[attachment=56890]
ABSTRACT
Microbial cellulases find applications in various industries and constitute a major group of the industrial enzymes.
Recently, there is resurgence in utilization of biomass for fuel production employing cellulases and hence forth in obtaining
better yields and novel activities. Improving the economics of such processes will involve cost reduction in cellulase
production which may be achieved by better bioprocesses and genetic improvement of cellulase producers to yield more of
the enzyme. The review discusses the current knowledge on cellulase production by microorganisms and the genetic
controls exercised on it. It discusses the industrial applications of cellulases and the challenges in cellulase research
especially in the direction of improving the process economics of enzyme production.
Introduction
Cellulose is the most common organic polymer,
representing about 1.5 × 1012 tons of the total annual
biomass production through photosynthesis especially
in the tropics, and is considered to be an almost
inexhaustible source of raw material for different
products1. It is the most abundant and renewable
biopolymer on earth and the dominating waste
material from agriculture2. A promising strategy for
efficient utilization of this renewable resource is the
microbial hydrolysis of lignocellulosic waste and
fermentation of the resultant reducing sugars for
production of desired metabolites or biofuel.
Microorganisms producing Cellulases
Cellulolytic microbes are primarily carbohydrate
degraders and are generally unable to use proteins or
lipids as energy sources for growth8. Cellulolytic
microbes notably the bacteria Cellulomonas and
Cytophaga and most fungi can utilize a variety of
other carbohydrates in addition to cellulose31-32, while
the anaerobic celluloytic species have a restricted
carbohydrate range, limited to cellulose and or its
hydrolytic products33-34. The ability to secrete large
amounts of extracellular protein is characteristic of
certain fungi and such strains are most suited for
production of higher levels of extracellular cellulases.
One of the most extensively studied fungi is
Trichoderma reesei, which converts native as well as
derived cellulose to glucose. Most commonly studied
cellulolytic organisms include: Fungal species-
Trichoderma, Humicola, Penicillium, Aspergillus;
Bacteria-Bacilli, Pseudomonads, Cellulomonas; and
Actinomycetes-Streptomyces, Actinomucor, and
Streptomyces.
Applications of Cellulases
Cellulases were initially investigated several
decades back for the bioconversion of biomass which
gave way to research in the industrial applications of
the enzyme in animal feed, food, textiles and
detergents and in the paper industry123. With the
shortage of fossil fuels and the arising need to find
alternative source for renewable energy and fuels,
there is a renewal of interest in the bioconversion of
lignocellulosic biomass using cellulases and other
enzymes. In the other fields, however, the
technologies and products using cellulases have
reached the stage where these enzymes have become
indispensable.
Concluding Remarks
The biological aspects of processing of cellulosic
biomass become the crux of future researches
involving cellulases and cellulolytic microorganisms.
The problems which warrants attention is not limited
to cellulase production alone, but a concerted effort in
understanding the basic physiology of cellulolytic
microbes and the utilization of this knowledge
coupled with engineering principles to achieve a
better processing and utilization of this most abundant
natural resource. The aspects open to consideration
include technologies for pre-treatment of cellulosic
materials for a better microbial attack, processes for
cost effective production of cellulases, treatment of
biomass for production of hydrolytic products, which
can then serve as substrates for downstream
fermentative production of valuable metabolites,
organism development by metabolic engineering, and
finally protein engineering to improve the properties
of enzymes to increase their specific activities,
process tolerance and stability.