Degradation of lignosulfonated compounds by Streptomyces viridosporus: effect of the culture medium and the nature of the lignosulfonate molecule

Abstract

Lignosulfonated compounds are by-products of the sulfite pulping of wood and have a higher level of biological resistance than lignin. Degradation of lignosulfonated compounds by Streptomyces viridosporus strain T7A growing on nutritive or chemically defined culture media was quantified. Two lignosulfonated compounds, differing in their molecular mass distribution and chemical structure, were used: lignosulfonate (1–80 kDa) and vanisperse, a sulfonated oxylignin (1–20 kDa). The use of nutritive culture medium (containing Biosoyase) allowed both the growth of S. viridosporus and the production of lignin peroxidase (LiP) leading to in vitro lignocellulose solubilization, but no lignosulfonate degradation was observed. Twenty per cent of the lignosulfonate underwent a molecular transformation, producing non-biodegradable acid precipitable polymeric lignin (lignosulfonate-APPL). When a defined culture medium (containing glycerol as additional organic carbon source) was used, LiP production was growth-associated. Under these conditions with periodic addition of glycerol, 21% of the lignosulfonate was degraded after 21 d of incubation. An inhibitory effect of lignosulfonate on biomass growth was suspected. When using vanisperse with the defined culture medium, a degradation yield of 35% was obtained after 20 d of incubation. S. viridosporus was unable to degrade a large amount of either lignosulfonated compound though significant modifications of the molecular mass distributions were observed by gel permeation chromatography.