Bacterial xylanases: biology to biotechnology
3 Biotech (2016) 6:150
DOI 10.1007/s13205-016-0457-z
REVIEW ARTICLE
Bacterial xylanases: biology to biotechnology
Hillol Chakdar1 • Murugan Kumar1 • Kuppusamy Pandiyan1 • Arjun Singh1 •
Karthikeyan Nanjappan1 • Prem Lal Kashyap1,2 • Alok Kumar Srivastava1
Received: 16 March 2016 / Accepted: 10 June 2016 / Published online: 30 June 2016
Ó The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract In this review, a comprehensive discussion
exclusively on bacterial xylanases; their gene organization;
different factors and conditions affecting enzyme yield and
activity; and their commercial application have been
deliberated in the light of recent research findings and
extensive information mining. Improved understanding of
biological properties and genetics of bacterial xylanase will
enable exploitation of these enzymes for many more
ingenious biotechnological and industrial applications.
Keywords Bacteria Xylanase Thermostability
Alkali stability Biotechnology
& Hillol Chakdar
Murugan Kumar
Kuppusamy Pandiyan
Arjun Singh
Karthikeyan Nanjappan
Prem Lal Kashyap
Alok Kumar Srivastava
1
ICAR-National Bureau of Agriculturally Important
Microorganisms (NBAIM), Kushmaur, Mau,
Uttar Pradesh 275103, India
2
ICAR-Indian Institute of Wheat and Barley Research
(IIWBR), Karnal, Haryana, India
Introduction
Xylan is the second most abundant polysaccharide in
nature present in both hard woods and annual plants. This
homopolysaccharide is as abundant as cellulose accounting for approximately one-third of the renewable organic
carbon sources on the earth (Kamble and Jadhav 2012).
Structure of xylan varies among different plant species and
its homopolymer backbone chain can be substituted with
different side chain groups at various positions (Wang
et al. 2014). Owing to its heterogeneity and complexity,
complete hydrolysis of xylan requires variety of cooperatively acting enzymes collectively known as xylanases.
Among various groups of microorganisms, bacteria and
fungi are endowed with powerful xylanolytic machinaries.
Xylanolytic microorganisms have been reported from
various extreme environments, such as thermal springs
(Bouacem et al. 2014), marines (Annamalai et al. 2009),
Antarctic environments (Bradner et al. 1999), and soda
lakes (Huang et al. 2015). Xylanases have wide range of
industrial and biotechnological applications. Their commercial exploitation in the area of food (Harris and
Ramalingam 2010), feed, and paper and pulp industries
(Polizeli et al. 2005) are well documented. Recently,
xylanases are also being used to increase the sugar
recovery from agricultural residues for biofuel production
(Gonçalves et al. 2015).
Due to huge industrial applications, a significant
research effort has been devoted towards mining and
characterization of xylanases. Initial focus had been on the
fungal xylanases due to their high activity, but constraints
faced during mass production and industrial applications,
placed bacterial xylanases as a tough competitor in the
industrial arena. Distribution, properties, genetics, and
application of the bacterial xylanases have been discussed
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in this review to highlight their real potential as a
promising source.
Xylan and xylanases
Structurally xylan is a homopolymer of D-xylopyranose
residues in b (1 ? 4) linkages with a degree of polymerization ranging from 150 to 200. This backbone is substituted by some of the sugars and organic acids, such as
arabinose, glucuronic acid, ferulic acid, etc. Xylans are
broadly categorized into four major groups based on its
substituents, viz., homoxylan, arabinoxylan, glucuronoxylan, and glucuronoarabinoxylan. Homoxylans contain
xylose residues only, and can be either linear or branched
(Sun et al. 2011). Arabinoxylans consist of a (1 ? 4)-bxylan main chain, but is substituted with a-arabinosyl
residues. The b-(1 ? 4)-linked D-xylopyranosyl residues
are substituted with one a-(1 ? 2)-linked 4-O-methyl-Dglucuronic acid in the case of glucuronoxylan; while in
glucuronoarabinoxylans, the same backbone is linked to
arabinofuranose and uronic acid (Gröndahl et al. 2003;
Bergmans et al. 1996). The side chains determine the solubility, physical conformation, and reactivity of xylan
molecule with other hemicellulosic components, and,
hence, greatly influence the mode and extent of enzymatic
cleavage.
Due to complexity in its structure, xylan needs different
enzymes collectively termed as xylanases for its complete
hydrolysis. Xylanases basically belong to hydrolase group
of enzymes, precisely to glycoside hydrolases. Sequencebased glycoside hydrolase classification has placed xylanase in two families GH10 and GH11, but xylanases are
also found in other glycoside hydrolase families, such as
GH5, 7, 8, and 43. Plant, fungal, and bacterial enzymes
comprise GH10 family, whereas GH11 family which is
structurally unrelated includes only fungal and bacterial
enzymes (Lafond et al. 2014). At least ten subfamilies of
xylanases, some of which are restricted to fungi (xylanases
Ia, Ib, Ic, II, IIIa, IIIb, and IV), and others to bacteria (A, B,
C). GH10 family is composed of both endo-1,4-b-xylanases and endo-1,3-b-xylanases, but the majority being
endo-1,4-b-xylanases with few endo-1,3-b-xylanases. They
have greater catalytic versatility and can catalyze hydrolysis of even cellulose and aryl b-D-cellobiosides. In mixed
linkage xylan, GH10 xylanases can attack on b-1,4-linkages that precede a b-1,3-linkage, but not the ones that
immediately follow b-1,3-linkages. GH10 xylanases can
attack b-1,3-linkages flanked on both sides by b-1,4-linkages. This family of xylanases can also tolerate replacement of one or two consecutive xylose residues by glucose
residues in the substrate. Members of this family are capable of hydrolyzing the aryl b-glycosides of xylobiose and
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xylotriose at the aglyconic bond. Furthermore, these
enzymes are highly active on short xylooligosaccharides,
thereby indicating small substrate-binding sites (Pollet
et al. 2010). Analyses of crystal structure, kinetic activity
on xylooligosaccharides, and end products have indicated
that family 10 xylanases typically have four-to-five substrate-binding sites. Most of the GH 10 xylanases typically
have high molecular mass, low pI, and (a/b)8-barrel fold
conformation (Teplitsky et al. 2000). GH11 members are
monospecific, as they consist exclusively of true endo-b1,4-xylanases that cleave internal b-1,4-xylosidic bonds.
Their catalytic versatility is lower than GH10 members,
and the products of their action can be further hydrolyzed
by the family 10 enzymes. These are considered as ‘‘true
xylanases’’, because of their exclusive action on D-xylose
containing substrates. Members of this family have low
molecular mass, high pI, and a wide range of pH optima
varying from 2 to 11. Like GH10 xylanases, these enzymes
can hydrolyze the aryl b-glycosides of xylobiose and
xy (...truncated)
