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.