Juana Rodríguez

Pyrolysis/gas chromatography/mass spectrometry as a useful technique to evaluate the ligninolytic action of streptomycetes on wheat straw

Abstract Pyrolysis/gas chromatography/mass spectrometry (Py/GC/MS) was used to elucidate whether the chemical modifications produced by streptomycetes on wheat straw are related with the lignocellulose degrading enzymes produced by the microorganism on such substrate. Thus, Streptomyces sp. UAH 47 was grown on wheat straw under solid-state fermentation and periodically the major solubilisation product of this substrate (lignin–carbohydrate complex) and the residual wheat straw were pyrolysed. In parallel, different enzyme activities related with lignocellulose degradation were evaluated. The characteristic pyrolysis products detected by GC/MS from both solubilised lignocarbohydrate complex and residual wheat straw demonstrated an oxidative action of the microorganism on the lignin. Either oxidation or oxidation followed by cleavage of the C3 alkyl chain, from S and G units, mainly at the Cα and Cβ position could be detected. A correlation between the oxidation degree of lignin and both l -3,4-dihydroxyphenylalanine and 2,6-dimethoxyphenol peroxidases produced by the strain can be inferred. Moreover, a liberation of ferulic and p -coumaric acids from the substrate was detected by HPLC, which probably involves the action of ferulic and coumaric acid esterases secreted by the microorganism. These enzymes could be partially responsible for the different pattern in the relative area of 4-vinylguaiacol and 4-vinylphenol detected in all samples along the incubation time. At last, the pyrolysis data suggest a straight correlation between the relative area of the compounds derived from carbohydrates and the pattern of hemicellulolytic and cellulolytic enzymes produced by the strain.

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.

13C NMR cross polarization and magic angle spinning (CPMAS) and gas chromatography/mass spectrometry analysis of the products from a soda pulp mill effluent decolourised by two Streptomyces strains

Abstract Two Streptomyces strains, UAH 30 and UAH 51, have been shown to decolourise a paper-mill effluent obtained after semichemical alkaline pulping of wheat straw. Fractionation of the effluent decolourised by strains UAH 30 and UAH 51 showed that 60% and 80% respectively of the alkali-lignin fraction have been removed from the effluent after 7 days of growth. 13C NMR cross polarization and magic angle spinning (CPMAS) spectra of the alkali-lignin remaining in the effluent after decolourisation revealed a decrease in the relative amount of aromatic lignin units compared to that obtained from the untreated effluent along with a reduction in the ratio of syringyl:guaiacyl units. Gas chromatography/mass spectrometry analysis of the low-molecular-mass compounds extracted from the decolourised effluent revealed the presence of new aromatic lignin-related compounds that were not present in the untreated control effluent. This was linked to a general depolymerization of larger lignin molecules occurring during decolourisation by the two Streptomyces strains. Identification of low-molecular-mass aromatic compounds extracted from the decolourised effluent revealed only the presence of p-hydroxyphenyl units in effluents decolourised by the strain UAH 30 while p-hydroxyphenyl, guaiacyl and syringyl units were detected in effluents decolourised by Streptomyces strain UAH 51. The study indicates that, while decolourisation is a common feature of the two Streptomyces strains, the mechanisms involved in the degradation of the lignin fractions may be different and strain-specific.

Characterization by Pyrolysis/Gas Chromatography/Mass Spectrometry of the Alkalilignin Obtained from Wheat Straw Soda-cooking Effluents After Treatment withStreptomycesStrains

Alkalilignin samples obtained from untreated paper-mill effluent and effluent decolorized by Streptomyces UAH 30 and Streptomyces UAH 51 were analyzed by pyrolysis/gas chromatography/mass spectrometry. The molecular composition of the samples and the chemical modifications occurring in the lignin units were studied in order to know the mechanism of decolorization carried out by these microorganisms. The pyrolysis data showed a notable reduction in the lignin pyrolysis products of alkalilignins in effluent decolorized by Streptomyces strains. Moreover, chemical modifications, such as oxidation and shortening of the side chain of the phenyl–propyl moieties of lignin were also detected.

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.