produce alkaline active xylanases that are optimally active at pH 9 and
10, respectively.
5.1 Properties
In general, the properties of enzymes are known to dictate their application potential.
Thus, enzyme studies often involve characterization which reveal their properties.
Studies have shown that alkaline active hemicellulases of a certain group (e.g.,
xylanases) exhibit astonishingly diverse properties. Probably, the only property
that is shared among alkaline active hemicellulases such as xylanases could be
their significant activity and stability in the alkaline pH range. The degree of
substrate specificity, the actual pH profile for activity and stability, the effect of
temperature on the activity and stability, molecular weight, end-product profile, etc.
vary from source to source. Some of the relevant properties of xylanases and
mannanases are discussed below.
5.1.1 Xylanases
Probably, xylanases are the most studied alkaline active hemicellulases. This may be
primarily driven by the application potential in pulp and paper industry. Since the
first xylanase from an alkaliphilic strain, Bacillus sp. C-59-2, was reported in 1973
[67], numerous alkaline active xylanases have been reported from alkaliphilic
organisms. This includes the xylanases produced by the alkaliphilic strains of
Bacillus [68–70], Micrococcus [71], Streptomyces [72], Alkalitalea [73],
Arthrobacter [74], Staphylococcus [75], Enterobacter [76], etc. Alkaline active
xylanases have also been reported from alkaliphilic fungal strains such as Aspergillus nidulans KK-99 [77] and Penicillium citrinum [78]. Alkaliphiles isolated from
soda lake and soil samples have been the major sources of alkaline active xylanases.
However, such xylanases have also been reported from insect gut microbes [68, 79]
and from metagenome libraries [80, 81].
Several xylanases from alkaliphilic strains have been purified and characterized.
Some of these enzymes are found to be optimally active around neutrality, and few
of them are even in the acidic range (Table 2). However, these enzymes, although
they are optimally active at neutral to acidic conditions, often exhibit reasonably
high activity at alkaline condition. Thus, these xylanases are active in a wide range of
pH. For instance, the alkaliphilic strain Bacillus firms K-1 produces a xylanase that is
optimally active at pH 5 but displays activity in the pH range of 3–12 [85]. Surprisingly, only few xylanases are known to be optimally active above pH 9 when
assayed at >50
C. These include Actinomadura Cpt20 [66], XylB from Bacillus
sp. AR-009 [87], and Bacillus halodurans xylanases [69, 98]. The most alkaline
active xylanase ever reported is the one from Streptomyces sp. CS802 which is
optimally active at pH 12 and stable even at pH 13 [72]. Although it is assayed at
258
G. Mamo
10, respectively.
5.1 Properties
In general, the properties of enzymes are known to dictate their application potential.
Thus, enzyme studies often involve characterization which reveal their properties.
Studies have shown that alkaline active hemicellulases of a certain group (e.g.,
xylanases) exhibit astonishingly diverse properties. Probably, the only property
that is shared among alkaline active hemicellulases such as xylanases could be
their significant activity and stability in the alkaline pH range. The degree of
substrate specificity, the actual pH profile for activity and stability, the effect of
temperature on the activity and stability, molecular weight, end-product profile, etc.
vary from source to source. Some of the relevant properties of xylanases and
mannanases are discussed below.
5.1.1 Xylanases
Probably, xylanases are the most studied alkaline active hemicellulases. This may be
primarily driven by the application potential in pulp and paper industry. Since the
first xylanase from an alkaliphilic strain, Bacillus sp. C-59-2, was reported in 1973
[67], numerous alkaline active xylanases have been reported from alkaliphilic
organisms. This includes the xylanases produced by the alkaliphilic strains of
Bacillus [68–70], Micrococcus [71], Streptomyces [72], Alkalitalea [73],
Arthrobacter [74], Staphylococcus [75], Enterobacter [76], etc. Alkaline active
xylanases have also been reported from alkaliphilic fungal strains such as Aspergillus nidulans KK-99 [77] and Penicillium citrinum [78]. Alkaliphiles isolated from
soda lake and soil samples have been the major sources of alkaline active xylanases.
However, such xylanases have also been reported from insect gut microbes [68, 79]
and from metagenome libraries [80, 81].
Several xylanases from alkaliphilic strains have been purified and characterized.
Some of these enzymes are found to be optimally active around neutrality, and few
of them are even in the acidic range (Table 2). However, these enzymes, although
they are optimally active at neutral to acidic conditions, often exhibit reasonably
high activity at alkaline condition. Thus, these xylanases are active in a wide range of
pH. For instance, the alkaliphilic strain Bacillus firms K-1 produces a xylanase that is
optimally active at pH 5 but displays activity in the pH range of 3–12 [85]. Surprisingly, only few xylanases are known to be optimally active above pH 9 when
assayed at >50
C. These include Actinomadura Cpt20 [66], XylB from Bacillus
sp. AR-009 [87], and Bacillus halodurans xylanases [69, 98]. The most alkaline
active xylanase ever reported is the one from Streptomyces sp. CS802 which is
optimally active at pH 12 and stable even at pH 13 [72]. Although it is assayed at
258
G. Mamo