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Special Issue "Biocatalytic Lignin Modification"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Molecular Diversity".

Deadline for manuscript submissions: closed (15 July 2015)

Special Issue Editor

Guest Editor
Prof. Anne S. Meyer

Center for BioProcess Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
Website | E-Mail
Interests: bioprocess enzyme technology

Special Issue Information

Dear Colleagues,

Biological modification of lignin has recently become revitalized as an important research object because degradation of lignin forms an important aspect of sustainable lignocellulosic plant biomass re-fining and lignin utilization. Lignin is a hydrophobic polymeric cell wall component that acts as a waterproof shield in plant cells, and lignin typically makes up 20%–30% of lignocellulosic biomass. Lignin is the only renewable plant polymer exclusively composed of aromatic structures – being made up of polymerized (dehydrogenated) p-hydroxycinnamyl alcohols. In Nature, white-rot fungi can degrade lignin, and research continues to reveal the enzymology of this process and to engineer biocatalysis of lignin by enzymes of fungal or bacterial origin – including heterologously expressed and improved enzymes. Recently, enzymatic modifications of lignin and improved enzymes for this process have come into focus paving the way for specific lignin modifications. From a chemical and analytical point of view, the analysis of biocatalytic lignin modification is challenging because lignin is insoluble in water and appears to lack steric regularity. In addition, lignins from various types of plant material are highly variable. This Special Issue will focus on disseminating the latest information in the fields of biocatalytic lignin modification and enzymology to foster cross-fertilization of knowledge and engineering aspects to provide progress in this field. It welcomes original research papers dealing with biological and biocatalytic lignin degradation and modification, chemistry, analysis, enzymology, enzyme discovery, and novel experimental approaches and technologies to examine and promote biocatalytic lignin modification and degradation.

Dr. Anne S. Meyer
Guest Editor

Manuscript Submission Information

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Keywords

  • lignin degradation
  • white-rot fungi
  • basidiomycetes
  • lignocellulose decay
  • laccase
  • lignin peroxidase
  • manganese peroxidase
  • enzyme discovery
  • analysis

Published Papers (5 papers)

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Research

Open AccessArticle Water-Soluble Lignins from Different Bioenergy Crops Stimulate the Early Development of Maize (Zea mays, L.)
Molecules 2015, 20(11), 19958-19970; doi:10.3390/molecules201119671
Received: 5 August 2015 / Revised: 19 October 2015 / Accepted: 23 October 2015 / Published: 5 November 2015
Cited by 6 | PDF Full-text (2273 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The molecular composition of water-soluble lignins isolated from four non-food bioenergy crops (cardoon CAR, eucalyptus EUC, and two black poplars RIP and LIM) was characterized in detail, and their potential bioactivity towards maize germination and early growth evaluated. Lignins were found to not
[...] Read more.
The molecular composition of water-soluble lignins isolated from four non-food bioenergy crops (cardoon CAR, eucalyptus EUC, and two black poplars RIP and LIM) was characterized in detail, and their potential bioactivity towards maize germination and early growth evaluated. Lignins were found to not affect seed germination rates, but stimulated the maize seedling development, though to a different extent. RIP promoted root elongation, while CAR only stimulated the length of lateral seminal roots and coleoptile, and LIM improved only the coleoptile development. The most significant bioactivity of CAR was related to its large content of aliphatic OH groups, C-O carbons and lowest hydrophobicity, as assessed by 31P-NMR and 13C-CPMAS-NMR spectroscopies. Less bioactive RIP and LIM lignins were similar in composition, but their stimulation of maize seedling was different. This was accounted to their diverse content of aliphatic OH groups and S- and G-type molecules. The poorest bioactivity of the EUC lignin was attributed to its smallest content of aliphatic OH groups and largest hydrophobicity. Both these features may be conducive of a EUC conformational structure tight enough to prevent its alteration by organic acids exuded from vegetal tissues. Conversely the more labile conformational arrangements of the other more hydrophilic lignin extracts promoted their bioactivity by releasing biologically active molecules upon the action of exuded organic acids. Our findings indicate that water-soluble lignins from non-food crops may be effectively used as plant biostimulants, thus contributing to increase the economic and ecological liability of bio-based industries. Full article
(This article belongs to the Special Issue Biocatalytic Lignin Modification)
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Open AccessArticle Glucuronoyl Esterase Screening and Characterization Assays Utilizing Commercially Available Benzyl Glucuronic Acid Ester
Molecules 2015, 20(10), 17807-17817; doi:10.3390/molecules201017807
Received: 15 July 2015 / Revised: 10 September 2015 / Accepted: 17 September 2015 / Published: 25 September 2015
Cited by 5 | PDF Full-text (1833 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Research on glucuronoyl esterases (GEs) has been hampered by the lack of enzyme assays based on easily obtainable substrates. While benzyl d-glucuronic acid ester (BnGlcA) is a commercially available substrate that can be used for GE assays, several considerations regarding substrate instability, limited
[...] Read more.
Research on glucuronoyl esterases (GEs) has been hampered by the lack of enzyme assays based on easily obtainable substrates. While benzyl d-glucuronic acid ester (BnGlcA) is a commercially available substrate that can be used for GE assays, several considerations regarding substrate instability, limited solubility and low apparent affinities should be made. In this work we discuss the factors that are important when using BnGlcA for assaying GE activity and show how these can be applied when designing BnGlcA-based GE assays for different applications: a thin-layer chromatography assay for qualitative activity detection, a coupled-enzyme spectrophotometric assay that can be used for high-throughput screening or general activity determinations and a HPLC-based detection method allowing kinetic determinations. The three-level experimental procedure not merely facilitates routine, fast and simple biochemical characterizations but it can also give rise to the discovery of different GEs through an extensive screening of heterologous Genomic and Metagenomic expression libraries. Full article
(This article belongs to the Special Issue Biocatalytic Lignin Modification)
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Open AccessArticle Enzymatic Transesterification of Kraft Lignin with Long Acyl Chains in Ionic Liquids
Molecules 2015, 20(9), 16334-16353; doi:10.3390/molecules200916334
Received: 7 July 2015 / Revised: 31 August 2015 / Accepted: 2 September 2015 / Published: 9 September 2015
Cited by 3 | PDF Full-text (3055 KB) | HTML Full-text | XML Full-text
Abstract
Valorization of lignin is essential for the economic viability of the biorefinery concept. For example, the enhancement of lignin hydrophobicity by chemical esterification is known to improve its miscibility in apolar polyolefin matrices, thereby helping the production of bio-based composites. To this end
[...] Read more.
Valorization of lignin is essential for the economic viability of the biorefinery concept. For example, the enhancement of lignin hydrophobicity by chemical esterification is known to improve its miscibility in apolar polyolefin matrices, thereby helping the production of bio-based composites. To this end and due to its many reactive hydroxyl groups, lignin is a challenging macromolecular substrate for biocatalyzed esterification in non-conventional media. The present work describes for the first time the lipase-catalyzed transesterification of Kraft lignin in ionic liquids (ILs). Three lipases, three 1-butyl-3-methylimidazolium based ILs and ethyl oleate as long chain acyl donor were selected. Best results were obtained with a hydrophilic/hydrophobic binary IL system (1-butyl-3-methylimidazolium trifluoromethanesulfonate/1-butyl-3-methylimidazolium hexafluoro- phosphate, 1/1 v/v) and the immobilized lipase B from Candida antarctica (CALB) that afforded a promising transesterification yield (ca. 30%). Similar performances were achieved by using 1-butyl-3-methylimidazolium hexafluorophosphate as a coating agent for CALB rather than as a co-solvent in 1-butyl-3-methylimidazolium trifluoromethane-sulfonate thus limiting the use of hydrophobic IL. Structural characterization of lignin oleate was performed by spectroscopic studies (FTIR and 1H-NMR). The synthesized lignin oleate exhibited interesting thermal and textural properties, different from those of the original Kraft lignin. Full article
(This article belongs to the Special Issue Biocatalytic Lignin Modification)
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Open AccessArticle Exploring the Oxidation of Lignin-Derived Phenols by a Library of Laccase Mutants
Molecules 2015, 20(9), 15929-15943; doi:10.3390/molecules200915929
Received: 15 July 2015 / Revised: 18 August 2015 / Accepted: 26 August 2015 / Published: 2 September 2015
Cited by 3 | PDF Full-text (1092 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Saturation mutagenesis was performed over six residues delimiting the substrate binding pocket of a fungal laccase previously engineered in the lab. Mutant libraries were screened using sinapic acid as a model substrate, and those mutants presenting increased activity were selected for exploring the
[...] Read more.
Saturation mutagenesis was performed over six residues delimiting the substrate binding pocket of a fungal laccase previously engineered in the lab. Mutant libraries were screened using sinapic acid as a model substrate, and those mutants presenting increased activity were selected for exploring the oxidation of lignin-derived phenols. The latter comprised a battery of phenolic compounds of interest due to their use as redox mediators or precursors of added-value products and their biological activity. The new laccase variants were investigated in a multi-screening assay and the structural determinants, at both the substrate and the protein level, for the oxidation of the different phenols are discussed. Laccase activity greatly varied only by changing one or two residues of the enzyme pocket. Our results suggest that once the redox potential threshold is surpassed, the contribution of the residues of the enzymatic pocket for substrate recognition and binding strongly influence the overall rate of the catalytic reaction. Full article
(This article belongs to the Special Issue Biocatalytic Lignin Modification)
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Open AccessArticle Laccase Gene Expression and Vinasse Biodegradation by Trametes hirsuta Strain Bm-2
Molecules 2015, 20(8), 15147-15157; doi:10.3390/molecules200815147
Received: 17 June 2015 / Revised: 11 August 2015 / Accepted: 13 August 2015 / Published: 19 August 2015
Cited by 1 | PDF Full-text (1116 KB) | HTML Full-text | XML Full-text
Abstract
Vinasse is the dark-colored wastewater that is generated by bioethanol distilleries from feedstock molasses. The vinasse that is generated from molasses contains high amounts of pollutants, including phenolic compounds and melanoindin. The goal of this work was to study the expression of laccase
[...] Read more.
Vinasse is the dark-colored wastewater that is generated by bioethanol distilleries from feedstock molasses. The vinasse that is generated from molasses contains high amounts of pollutants, including phenolic compounds and melanoindin. The goal of this work was to study the expression of laccase genes in the Trametes hirsuta strain Bm-2, isolated in Yucatan, Mexico, in the presence of phenolic compounds, as well as its effectiveness in removing colorants from vinasse. In the presence of all phenolic compounds tested (guaiacol, ferulic acid, and vanillic acid), increased levels of laccase-encoding mRNA were observed. Transcript levels in the presence of guaiacol were 40 times higher than those in the control. The lcc1 and lcc2 genes of T. hirsuta were differentially expressed; guaiacol and vanillin induced the expression of both genes, whereas ferulic acid only induced the expression of lcc2. The discoloration of vinasse was concomitant with the increase in laccase activity. The highest value of enzyme activity (2543.7 U/mL) was obtained in 10% (v/v) vinasse, which corresponded to a 69.2% increase in discoloration. This study demonstrates the potential of the Bm-2 strain of T. hirsuta for the biodegradation of vinasse. Full article
(This article belongs to the Special Issue Biocatalytic Lignin Modification)
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