Lignocarbohydrate Solubilization from Straw by Actinomycetes

Abstract

Actinomycetes grown on wheat straw solubilized a lignocarbohydrate fraction which could be recovered by acid precipitation. Further characterization of this product (APPL) during growth of Streptomyces sp. strain EC1 revealed an increase in carboxylic acid and phenolic hydroxyl content, suggesting progressive modification. This was also observed in dioxane-extracted lignin fractions of degraded straw, and some similarity was further suggested by comparative infrared spectroscopy. However, the molecular weight profile of APPL was relatively constant during growth of Streptomyces sp. strain EC1 on straw, while analysis of the dioxane-extracted lignin fractions appeared to show fragmentation followed by repolymerization. Lignocarbohydrate solubilization could be monitored in all cultures by routine assay of APPL-associated protein, which accounted for up to 20% of the extracellular culture protein in some cases. Interestingly, this protein fraction was found to include active hydrolytic and oxidative enzymes involved in the degradation of lignocellulose, and specific enzyme activities were often increased in the acid-insoluble fractions of culture supernatants. This was particularly important for peroxidase and veratryl oxidase activities, which could be readily detected in the acid-precipitable lignocarbohydrate complex but were virtually undetectable in untreated culture supernatants.