Lignocellulose-degrading microbial consortia:Importance of synergistic interactions

Lignocellulose biomass (LCB) represents a cheap source of carbon that can be transformed into valuable (energy) compounds. Nevertheless, its application at large scale is still limited to date. The aims of this thesis were (1) to generate a better understanding of the driving forces in the selection of specialized lignocellulolytic microbial consortia, (2) to develop a specialized consortium able to degrade recalcitrant LCB and (3) to obtain fundamental knowledge about cooperative interactions in the LCB degrader consortia. The results of the study revealed that the composition of the LCB determined the final structure of the consortia, whereas the inoculum source determined the initial composition of the consortia as well as the stability of the final consortia. Moreover, all consortia bred on wheat straw at standard salt levels contained a core set of bacteria, consisting of members of the Enterobacteriaceae, Xanthomonadaceae, Pseudomonadaceae and Sphingobacteriaceae. In contrast, consortia bred on wheat straw at raised salt levels consisted of Flavobacteriaceae, Cyclobacteriaceae, Pseudomonadaceae and Halomonadaceae. Only Pseudomonas sp. and Flavobacterium sp. were present in all selected consortia. Then, in an effort to understand the cooperative relationships in LCB degrader consortia, S. multivorum w15 and C. freundii so4 (the most synergistic strains) were selected for further study. The possible interactive mechanisms within this collaborative pair were related to different and complementary hydrolytic enzyme systems as well as metabolites present in the supernatants of each of the two strains. Possibly, strain w15 acted as a primary degrader (decomposing a primary energy source), producing compounds that strain so4 can consume (secondary degrader). Strain so4 could also be excreting secondary metabolites, contributing to stress response modulation