María E. Arias

Advanced oxidation of benzene, toluene, ethylbenzene and xylene isomers (BTEX) by Trametes versicolor

Advanced oxidation of benzene, toluene, ethylbenzene, and o-, m-, and p-xylene (BTEX) by the extracellular hydroxyl radicals (*OH) generated by the white-rot fungus Trametes versicolor is for the first time demonstrated. The production of *OH was induced by incubating the fungus with 2,6-dimethoxy-1,4-benzoquinone (DBQ) and Fe3+-EDTA. Under these conditions, *OH were generated through DBQ redox cycling catalyzed by quinone reductase and laccase. The capability of T. versicolor growing in malt extract medium to produce *OH by this mechanism was shown during primary and secondary metabolism, and was quantitatively modulated by the replacement of EDTA by oxalate and Mn2+ addition to DBQ incubations. Oxidation of BTEX was observed only under *OH induction conditions. *OH involvement was inferred from the high correlation observed between the rates at which they were produced under different DBQ redox cycling conditions and those of benzene removal, and the production of phenol as a typical hydroxylation product of *OH attack on benzene. All the BTEX compounds (500 microM) were oxidized at a similar rate, reaching an average of 71% degradation in 6 h samples. After this time oxidation stopped due to O2 depletion in the closed vials used in the incubations.

Chemical characterization by pyrolysis/gas chromatography/mass spectrometry of acid-precipitable polymeric lignin (APPL) from wheat straw transformed by selected streptomyces strains

Abstract The possible differential biodegradation of wheat straw performed by different Streptomyces strains was investigated on solid-state fermentation conditions. The modified lignin polymer named acid-precipitable polymeric lignin (APPL), harvested with NaOH or water, from wheat straw transformed by selected Streptomyces strains was tentatively characterized by pyrolysis-gas chromatography-mass spectrometry (PY/GC/MS). For comparative analyzes, lignin-carbohydrate-protein complexes obtained from uninoculated wheat straw were used as controls. Significant differences in the p-hydroxyphenyl: guaiacyl: syringyl(H: G: S) and in the syringyl guaiacyl ( S G ) ratios of the APPLs extracted with water from wheat straw transformed by the strains Streptomyces UAH 23, Streptomyces UAH 52 and Streptomyces viridosporus T7 A were detected compared with the control. While S. UAH 23 produced a preferential degradation of the non-condensed Slignin units, a decrease in the condensed G-units was produced byS. UAH 52 and S. viridosporus T7 A. From the results obtained it can be concluded that PY/GC/MS is a suitable technique to establish differences in the composition of the main product of solubilization of lignocellulose by different Streptomyces strains. Nevertheless for chemical characterization of this polymer, it is important to select the method to be used to extract the APPL from degraded residues in order to prevent chemical modifications of the substrate as occurred when NaOH was used which make difficult to attribute the changes observed to the microbial activity.

Production and partial characterization of extracellular peroxidases produced bystreptomyces avermitilis UAH30

The effect of a number of environmental parameters (pH, temperature, carbon and nitrogen ratio of nutrient) on the production of extracellular peroxidase enzymes byStreptomyces avermitilis UAH30 was examined. Maximum specific peroxidase activity (0.12 U/mg of protein) was obtained after 72 hours of 1 incubation at 45‡C in a minimal salt medium (pH 7.5) containing 0.6% (w/v) yeast extract and 0.6% (w/v) xylan corresponding to a C:N ratio of 4 to 1. A study of the effect of incubation on peroxidase activity showed that the enzyme was stable and active for at least one hour after incubation at 50‡C while at higher temperatures the stability and activity of the peroxidase was reduced such that at 60‡C the peroxidase activity has a half life of 20 min while at 80‡C the half life was reduced to 5 min. The activation energy for deactivation as a result of thermal denaturation of the enzyme was calculated to be 80 ±7 kJ/mol. The optimum pH for the activity occurred between a pH range of 6.5–8.5 with pKa1 and pKa2 of 5.1 ±0.1 and 9.7 ±0.1, respectively. The Km and Vmax for the peroxidase activity were determined to be 1.45 mM and 0.31 unit per mg protein respectively using 2,4dicholorophenol (2,4-DCP) as a substrate. Characterization of the peroxidase activity revealed activity against L,3–4 dihydroxyphenylalanine and guaiacol, while no inhibition of peroxidase activity could be detected with the haem inhibitors such as potassium cyanide and sodium azide, suggesting the lack of haem component in the tertiary structure. Aspects of using the crude peroxidase preparation in the pulp and paper industry are discussed.

Analysis of alkali-lignin in a paper mill effluent decolourised with two Streptomyces strains by gas chromatography–mass spectrometry after cupric oxide degradation

Alkali-lignin samples obtained from an untreated paper mill effluent and from the effluent decolourised by the strains Streptomyces avermitilis CECT 3339 and Streptomyces scabies UAH 51 were analysed by gas chromatography-mass spectrometry (GC-MS) after cupric oxide degradation. The analysis of the depolymerisation products of the alkali-lignin from the decolourised effluents showed a strain specific modification of the aromatic moiety of the alkali-lignin. Moreover, both strains were able to breakdown the aryl-alkyl ether linkages between the cinnamic acids and the lignin. Finally, GC-MS analysis showed that both strains oxidised the alkali-lignin regardless of its initial degree of oxidation.

Degradation of alkali-lignin residues from solid-state fermentation of wheat straw by streptomycetes

The ability of three Streptomyces strains to degradealkali-lignin, produced from the treatment of wheat straw by the same organisms, was examined. Decolourisation and loss of alkali-lignin was only detected in cultures supplemented with ammonium as an inorganic N source. The pH of cultures supplemented with inorganic N reached lower pH than in those supplemented with yeast extract. From FT-IR spectra corresponding to the alkali-lignin obtained from the same cultures, a degradation of carbohydrate component concomitant with a modification in the aromatic moiety of lignin could be inferred. The results indicate that streptomycetes are suitable for use in the treatment of alkali-lignin effluents from the biological treatment of wheat straw by the same organisms and therefore support the role for these organisms in the development of clean technologies in pulp and paper industry.

Comparison of the efficiency of bacterial and fungal laccases in delignification and detoxification of steam-pretreated lignocellulosic biomass for bioethanol production

This study evaluates the potential of a bacterial laccase from Streptomyces ipomoeae (SilA) for delignification and detoxification of steam-exploded wheat straw, in comparison with a commercial fungal laccase from Trametes villosa. When alkali extraction followed by SilA laccase treatment was applied to the water insoluble solids fraction, a slight reduction in lignin content was detected, and after a saccharification step, an increase in both glucose and xylose production (16 and 6%, respectively) was observed. These effects were not produced with T. villosa laccase. Concerning to the fermentation process, the treatment of the steam-exploded whole slurry with both laccases produced a decrease in the phenol content by up to 35 and 71% with bacterial and fungal laccases, respectively. The phenols reduction resulted in an improved performance of Saccharomyces cerevisiae during a simultaneous saccharification and fermentation (SSF) process, improving ethanol production rate. This enhancement was more marked with a presaccharification step prior to the SSF process.

Influence of process variables on the properties of laccase biobleached pulps

A laccase stage can be used as a pre-treatment of a standard chemical bleaching sequence to reduce environmental concerns associated to this process. The importance of each independent variable and its influence on the properties of the bleached pulp have been studied in depth in this work, using an adaptive network-based fuzzy inference system (ANFIS) with four independent variables (laccase, buffer, mediator and oxygen) as input. Eucalyptus globulus kraft pulp was biobleached using a laccase from Pycnoporus sanguineus and a natural mediator (acetosyringone). Later, an alkaline extraction and a hydrogen peroxide treatment were applied. Most biobleaching processes showed a decrease in kappa number and an increase in brightness with no significant impact on the viscosity values, compared with the control. Oxygen was the variable with the smallest influence on the final pulp properties while the laccase and buffer solution showed a significant influence.

Decolorization and detoxification of textile dyes using a versatile Streptomyces laccase-natural mediator system

Currently, there is increasing interest in assessing the potential of bacterial laccases for industrial and environmental applications especially in harsh conditions. The environmental impact of the textile industry requires novel and effective technologies to mitigate the presence of dyes in wastewaters before discharging into the environment. Dyes usually remain stable in the presence of a variety of chemicals, light and are recalcitrant to microbial degradation. Among available technologies the biological treatments offer environmentally friendly strategies for decolorizing and detoxifying these compounds. The recent discovery of versatile laccases in streptomycetes opens up new opportunities for their commercial application. The aim of this study is to assess the potential of a novel bacterial laccase SilA produced by Streptomyces ipomoeae CECT 3341 active over wide temperature and pH ranges for use as an eco-friendly, biological treatment for the degradation of textile dyes. Insights into the enhancement of the oxidative action of this enzyme through the use of natural redox mediators are presented together with an assessment of the potential toxicity of the degradation products. Our results confirm that the combination of the laccase and natural mediators such as acetosyringone and methyl syringate enhanced the decolorization and detoxification of a variety of textile dyes up to sixfold and 20-fold, respectively. Mediator concentration was found to have a significant effect (p < 0.05) on dye decolorization at 60 °C; thus, the decolorization of Acid Orange 63 increased from 6 to 70-fold when the mediator concentration was increased from 0.1 to 0.5 mM. Further, the toxicity of tartrazine decreased 36-fold when the SilA-MeS system was used to decolorize the dye. The thermal properties of the SilA coupled with the stability of SilA at high pH suggest a potential commercial application for use in the decolorization of textile wastewaters which generally are performed at high temperature (>55 °C) and salinity and neutral pH, conditions which are unfavourable for conventional fungal laccases.