Transcriptomic analysis of lignocellulose degradation by Streptomyces coelicolor A3(2) and elicitation of secondary metabolites production.

Streptomyces coelicolor A3(2) is considered as the model strain among the Streptomyces and has the capacity to produce several natural molecules. Our hypothesis was that cultivation of the strain onto a complex carbon source such as wheat bran (WB) would induce the production of various secondary metabolites due to the presence of complex polysaccharides. A multiapproach has been performed in order to investigate: (1) whether that strain could degrade lignocellulose; (2) which enzymatic and metabolic pathways secondary were over-expressed when grown on WB. The transcriptomic approach showed the expression of several CAZymes significantly expressed when grown on WB such as endoglucanases (encoding for GH74, GH5_8, and GH12) and xylanases (GH11 and CE4 encoding for respectively endo-1,4-beta-xylanase and an acetyl-xylan esterase). Enzymatic activities showed an expression of xylanase (115.3 ± 32.2 mUI/ml) and laccase-peroxidase (101.5 ± 10.9 mUI/ml) during WB degradation by S. coelicolor A3(2). Metabolomics showed that the production of secondary metabolites differed between growth on either glucose or WB as carbon source, which may be correlated to the complexity of carbon compounds within WB, which are similar to the ones encountered in soils and should represent more the in situ carbon conditions which Streptomyces might face off. This opens opportunities for the bioproduction of molecules of interest from WB.

Co-elicitation of lignocelluloytic enzymatic activities and metabolites production in an Aspergillus-Streptomyces co-culture during lignocellulose fractionation.

Lignocellulose, the most abundant biomass on Earth, is a complex recalcitrant material mainly composed of three fractions: cellulose, hemicelluloses and lignins. In nature, lignocellulose is efficiently degraded for carbon recycling. Lignocellulose degradation involves numerous microorganisms and their secreted enzymes that act in synergy. Even they are efficient, the natural processes for lignocellulose degradation are slow (weeks to months). In this study, the objective was to study the synergism of some microorganisms to achieve efficient and rapid lignocellulose degradation. Wheat bran, an abundant co-product from milling industry, was selected as lignocellulosic biomass. Mono-cultures and co-cultures involving one A.niger strain fungi never sequenced before (DSM 1957) and either one of three different Streptomyces strains were tested in order to investigate the potentiality for efficient lignocellulose degradability. Comparative genomics of the strain Aspergillus niger DSM 1957 revealed that it harboured the maximum of AA, CBM, CE and GH among its closest relative strains. The different co-cultures set-up enriched the metabolic diversity and the lignocellulolytic CAZyme content. Depending on the co-cultures, an over-expression of some enzymatic activities (xylanase, glucosidase, arabinosidase) was observed in the co-cultures compared to the mono-cultures suggesting a specific microbial cross-talk depending on the microbial partner. Moreover, metabolomics for each mono and co-culture was performed and revealed an elicitation of the production of secondary metabolites and the activation of silent biosynthetic cluster genes depending on the microbial co-culture. This opens opportunities for the bioproduction of molecules of interest from wheat bran.