regulated (Abdelaziz et al. 2016). Among the several lignin-degrading microbes
studied so far, ortho or β-KA cleavage pathway was found to be dominant pathway
(Bugg et al. 2011b).
4.5
Bacterial Enzymes Responsible for Funneling Lignin and
Its Degradation Intermediates
The major lignin-degrading or modifying enzymes responsible for utilization of
lignin or its degradation intermediates are detailed in the following sections.
4.5.1 DyP-Type Peroxidases
DyP-type peroxidases (DyPs) are heme-containing new class of peroxidase recently
identified and are predominantly present in bacteria. This enzyme is also present in
fungi, first discovered from Bjerkandera adusta and named so by studying their
activity on anthraquinone and azo-dyes (Sugano et al. 2007). Bacterial DyPs have
low redox potential than fungal DyPs, but they showed activity toward phenolic as
well as nonphenolic compounds. They can perform catalysis by utilizing H 2 O 2 and
without H 2 O 2 as oxygenase or hydrolase. The first extracellular lignin-degrading
peroxidase from bacteria has been reported in S. viridosporus T7A, and after
genomic analysis it was assumed to be DyP (Ramachandra et al. 1988). Several
other peroxidases have been reported from this strain responsible for degradation of
β-aryl bonds, the most predominant bond in lignin. DyPs were characterized from
Rhodococcus jostii RHA1, Pseudomonas fluorescens Pf-5, Amycolatopsis sp.
75iv2ATCC, Bacillus subtilis KCTC2023, Pseudomonas putida MET94,
Saccharomonospora viridis DSM 43017, Thermobifida fusca. Their broad substrate
range (synthetic dyes, Kraft lignin, lignin model compounds, monophenolic
compounds, veratryl alcohol, carotenes, Mn
+2 ) and mechanism of action have also
been discussed (de Gonzalo et al. 2016;Priyadarshinee et al. 2016; Bugg et al. 2016).
The reaction catalyzed by DyPs has been shown in Fig. 4.5.
4.5.2 Laccase (Benzenediol: Oxygen Oxidoreductases; EC
1.10.3.2; AA1)
Laccases are multicopper oxidase that oxidizes various aromatic compounds
(phenolics) with reduction of oxygen molecule to water as byproduct. These are
extensively distributed among plants, fungi, insects, and bacteria (Riva 2006; Munk
et al. 2015). Laccase mostly contains three structural domains, but one or two
domains may be lacking in some laccases. Laccase have 4 copper atoms, and
these are classified into three groups (type) based on spectral and paramagnetic
properties. The type1 (T1) gives blue color (λmax. 600 nm), and it is the main site
where oxidation of substrate takes place, Type 2 (T2) contains one copper (EPR
94
M. Kumar et al.
studied so far, ortho or β-KA cleavage pathway was found to be dominant pathway
(Bugg et al. 2011b).
4.5
Bacterial Enzymes Responsible for Funneling Lignin and
Its Degradation Intermediates
The major lignin-degrading or modifying enzymes responsible for utilization of
lignin or its degradation intermediates are detailed in the following sections.
4.5.1 DyP-Type Peroxidases
DyP-type peroxidases (DyPs) are heme-containing new class of peroxidase recently
identified and are predominantly present in bacteria. This enzyme is also present in
fungi, first discovered from Bjerkandera adusta and named so by studying their
activity on anthraquinone and azo-dyes (Sugano et al. 2007). Bacterial DyPs have
low redox potential than fungal DyPs, but they showed activity toward phenolic as
well as nonphenolic compounds. They can perform catalysis by utilizing H 2 O 2 and
without H 2 O 2 as oxygenase or hydrolase. The first extracellular lignin-degrading
peroxidase from bacteria has been reported in S. viridosporus T7A, and after
genomic analysis it was assumed to be DyP (Ramachandra et al. 1988). Several
other peroxidases have been reported from this strain responsible for degradation of
β-aryl bonds, the most predominant bond in lignin. DyPs were characterized from
Rhodococcus jostii RHA1, Pseudomonas fluorescens Pf-5, Amycolatopsis sp.
75iv2ATCC, Bacillus subtilis KCTC2023, Pseudomonas putida MET94,
Saccharomonospora viridis DSM 43017, Thermobifida fusca. Their broad substrate
range (synthetic dyes, Kraft lignin, lignin model compounds, monophenolic
compounds, veratryl alcohol, carotenes, Mn
+2 ) and mechanism of action have also
been discussed (de Gonzalo et al. 2016;Priyadarshinee et al. 2016; Bugg et al. 2016).
The reaction catalyzed by DyPs has been shown in Fig. 4.5.
4.5.2 Laccase (Benzenediol: Oxygen Oxidoreductases; EC
1.10.3.2; AA1)
Laccases are multicopper oxidase that oxidizes various aromatic compounds
(phenolics) with reduction of oxygen molecule to water as byproduct. These are
extensively distributed among plants, fungi, insects, and bacteria (Riva 2006; Munk
et al. 2015). Laccase mostly contains three structural domains, but one or two
domains may be lacking in some laccases. Laccase have 4 copper atoms, and
these are classified into three groups (type) based on spectral and paramagnetic
properties. The type1 (T1) gives blue color (λmax. 600 nm), and it is the main site
where oxidation of substrate takes place, Type 2 (T2) contains one copper (EPR
94
M. Kumar et al.