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

Lignosulfonated compounds are by-products of the sulfite pulping of wood an d have a higher level of biological resistance than lignin. Degradation of lignosulfonated compounds by Streptomyces viridosporus strain T7A growing o n nutritive or chemically defined culture media was quantified. Two lignosu lfonated compounds, differing in their molecular mass distribution and chem ical structure, were used: lignosulfonate (1-80 kDa) and vanisperse, a sulf onated oxylignin (1-20 kDa). The use of nutritive culture medium (containin g Biosoyase) allowed both the growth of S. viridosporus and the production of lignin peroxidase (LiP) leading to in vitro lignocellulose solubilizatio n, but no lignosulfonate degradation was observed. Twenty per cent of the l ignosulfonate underwent a molecular transformation, producing non-biodegrad able acid precipitable polymeric lignin (lignosulfonate-APPL). When a defin ed culture medium (containing glycerol as additional organic carbon source) was used, LiP production was growth-associated. Under these conditions wit h periodic addition of glycerol, 21% of the lignosulfonate was degraded aft er 21 d of incubation. An inhibitory effect of lignosulfonate on biomass gr owth was suspected. When using vanisperse with the defined culture medium, a degradation yield of 35% was obtained after 20 d of incubation. S. virido sporus was unable to degrade a large amount of either lignosulfonated compo und though significant modifications of the molecular mass distributions we re observed by gel permeation chromatography. (C) 1999 Elsevier Science Ltd . All rights reserved.