Upgrading of an industrial lignin by using laccase produced by Fusarium proliferatum and different laccase-mediator systems

Laccase/Mediator Systems: Their Reactivity toward Phenolic Lignin Structures

Laccase-mediator systems (LMS) have been widely studied for their capacity to oxidize the nonphenolic subunits of lignin (70-90% of the polymer). The phenolic subunits (10-30% of the polymer), which can also be oxidized without mediators, have received considerably less attention. Consequently, it remains unclear to what extent the presence of a mediator influences the reactions of the phenolic subunits of lignin. To get more insight in this, UHPLC-MS was used to study the reactions of a phenolic lignin dimer (GBG), initiated by a laccase from Trametes versicolor, alone or in combination with the mediators HBT and ABTS. The role of HBT was negligible, as its oxidation by laccase occurred slowly in comparison to that of GBG. Laccase and laccase/HBT oxidized GBG at a comparable rate, resulting in extensive polymerization of GBG. In contrast, laccase/ABTS converted GBG at a higher rate, as GBG was oxidized both directly by laccase but also by ABTS radical cations, which were rapidly formed by laccase. The laccase/ABTS system resulted in Cα oxidation of GBG and coupling of ABTS to GBG, rather than polymerization of GBG. Based on these results, we propose reaction pathways of phenolic lignin model compounds with laccase/HBT and laccase/ABTS.

Spectroscopic analyses of the biofuels-critical phytochemical coniferyl alcohol and its enzyme-catalyzed oxidation products

Lignin composition (monolignol types of coniferyl, sinapyl or p-coumaryl alcohol) is causally related to biomass recalcitrance. We describe multiwavelength (220, 228, 240, 250, 260, 290, 295, 300, 310 or 320 nm) absorption spectroscopy of coniferyl alcohol and its laccase- or peroxidase-catalyzed products during real time kinetic, pseudo-kinetic and endpoint analyses, in optical turn on or turn off modes, under acidic or basic conditions. Reactions in microwell plates and 100 μL volumes demonstrated assay miniaturization and high throughput screening capabilities. Bathochromic and hypsochromic shifts along with hyperchromicity or hypochromicity accompanied enzymatic oxidations by laccase or peroxidase. The limits of detection and quantitation of coniferyl alcohol averaged 2.4 and 7.1 μM respectively, with linear trend lines over 3 to 4 orders of magnitude. Coniferyl alcohol oxidation was evident within 10 minutes or with 0.01 μg/mL laccase and 2 minutes or 0.001 μg/mL peroxidase. Detection limit improved to 1.0 μM coniferyl alcohol with Km of 978.7 ± 150.7 μM when examined at 260 nm following 30 minutes oxidation with 1.0 μg/mL laccase. Our assays utilized the intrinsic spectroscopic properties of coniferyl alcohol or its oxidation products for enabling detection, without requiring chemical synthesis or modification of the substrate or product(s). These studies facilitate lignin compositional analyses and augment pretreatment strategies for reducing biomass recalcitrance.

On the diversity of the laccase gene: a phylogenetic perspective from Botryosphaeria rhodina (Ascomycota: Fungi) and other related taxa

The present study is the first describing the sequencing of a fragment of the copper-oxidase domain of a laccase gene in the family Botryosphaeriaceae. The aim of this work was to assess the degree of genetic and evolutionary relationships of a laccase gene from Botryosphaeria rhodina MAMB-05 with other ascomycete and basidiomycete laccase genes. The 193-amino acid sequences of the copper-oxidase domain from several different fungi, insects, a plant, and a bacterial species were retrieved from GenBank and aligned. Phylogenetic analyses were performed using neighbor-joining, maximum parsimony, and Bayesian inference methods. The organisms studied clustered into five gene clades: fungi (ascomycetes and basidiomycetes), insects, plants, and bacteria. Also, the topologies showed that fungal laccases of the ascomycetes and basidiomycetes are clearly separated into two distinct clusters. This evidence indicated that B. rhodina MAMB-05 and other closely related ascomycetes are a new biological resource given the biotechnological potential of their laccase genes.

Laccase-HBT bleaching of eucalyptus kraft pulp: influence of the operating conditions

Different operating conditions (viz. pulp consistency, oxygen pressure and treatment time) in the biobleaching of eucalyptus kraft pulp with the laccase-HBT system was tested in order to describe their effect and normalize a biobleaching protocol. A high O(2) pressure (0.6MPa) was found to result in improved laccase-assisted delignification of the pulp. Also, a high pulp consistency (10%) and a short treatment time (2h) proved the best choices with a view to obtaining good pulp properties (kappa number and ISO brightness) under essentially mild conditions. The laccase-HBT treatment was found to result in slight delignification (in the form of a 20-27% decrease in kappa number); however, an alkaline extraction stage raised delignification to 41-45%, a much higher level than those obtained in the control tests (16-23%). Also, the use of hydrogen peroxide in the extraction stage resulted in improved brightness (14-19%), but in scarcely improved delignification (4-7%). Treating the pulp with the laccase-HBT system reduced the amount of hydrogen peroxide required for subsequent alkaline bleaching by a factor of 3-4 relative to control tests.

Comparative study of the efficiency of synthetic and natural mediators in laccase-assisted bleaching of eucalyptus kraft pulp

The natural phenolic compounds syringaldehyde and vanillin were compared to the synthetic mediators 1-hydroxybenzotriazole, violuric acid and promazine in terms of boosting efficiency in a laccase-assisted biobleaching of eucalyptus kraft pulp. Violuric acid and 1-hydroxybenzotriazole revealed to be the most effective mediators of the bioprocess. Nevertheless, laccase-syringaldehyde system also improved the final pulp properties (28% delignification and 63.5% ISO brightness) compared to the process without mediator (23% and 61.5% respectively), in addition to insignificant denaturation effect over laccase. The efficiency of the biobleaching process was further related to changes in non-conventionally used optical and chromatic parameters of pulp, such as (L*), chroma (C*) and dye removal index (DRI) showing good correlation. Adverse coupling reactions of the natural phenolic mediators on pulp lignin were predicted by electrochemical studies, demonstrating the complexity of the laccase-mediator reaction on pulp.

An alkali-stable enzyme with laccase activity from entophytic fungus and the enzymatic modification of alkali lignin

Mycelia Sterilia YY-5, an entophytic fungus, was isolated from Rhus chinensis Mill and its extracellular enzyme had a higher laccase activity (MS-Lac). After been purified by anion exchange and gel filtration chromatography, MS-Lac, which had a molecular mass of 45 kDa, was found to be an alkali-stable enzyme with an optimum pH of 10.0 and capable of retaining 80% activity after incubation for 72 h with syringaldazine as substrate. It was also found that syringaldazine had a higher affinity than 2,2'-azino-bis-(3-ethylbenzothiazoline)-6-sulphonate (ABTS) as substrate for MS-Lac, which was determined in sodium phosphate buffer (pH 6.0, 0.1M) at 30 degrees C. Meanwhile, the lignin modification, catalyzed by MS-Lac, indicated that it could oxidize the phenolic hydroxyl, side chain substituent or carbonyl group of spruce alkali lignin in cetyltrimethylammonium bromide (CTAB) reversed micelles (20 mM, pH 6.0, W/O=40) and steam-exploded wheat straw alkali lignin in NaOH solution (20 mM, pH 10.0).

Early attack and subsequent changes produced in an industrial lignin by a fungal laccase and a laccase-mediator system: an analytical approach

An industrial kraft pine lignin (Indulin AT, KL) was characterized and treated in both aqueous-buffered media and dioxane to water, either with a partially purified laccase from Fusarium proliferatum or with the laccase plus 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic-acid (ABTS) as mediator. The changes in the lignin after different incubation periods were analyzed through the application of high performance liquid chromatography (HPLC), UV-visible (Vis) spectroscopy and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). At the onset of incubation, laccase-treated samples showed a slight polymerization and strong modifications in UV-Vis spectra. Through Py-GC/MS, a decrease in phenolic and methoxy-bearing pyrolysis products was observed, in contrast to an increase in the more oxidized products. After longer incubation periods (48 h) a substantial polymerization was detected by HPLC, along with a decrease in the guaiacyl (G) units. In contrast, the analysis by HPLC of the samples recovered from the laccase-ABTS system (LMS) showed an intense depolymerization, accompanied by a sizeable loss in G units and a decrease in the methyl and ethyl side-chain phenolic compounds. These results provide conclusive evidence of a rapid initial attack of the industrial lignin by laccase and notable modifications in the KL after longer incubation periods with laccase or LMS.