3 Search Results

Biological lignin valorization to fuels and value-added chemicals enables sustainable and economic biorefineries. Even though significant progress has been made, several major challenges arose due to high recalcitrance and heterogeneity of lignin, which needs to be addressed to improve lignin processing. This work demonstrates an overview of biological lignin conversion and its regulation from a metabolic engineering and systems biology viewpoint. Biological lignin valorization includes three stages: lignin depolymerization, aromatics degradation, and target product biosynthesis. Ligninolytic microorganisms have an extensive enzymatic toolbox to break down the lignin and convert heterogeneous lignin derivatives to central intermediates, such as protocatechuate or catechol,more » through a peripheral pathway. These intermediates undergo ring cleavage via the β-ketoadipate pathway and are ultimately transformed into metabolites by yielding acetyl-CoA for internal product biosynthesis, such as triacylglycerols, polyhydroxyalkanoates, etc. Bioprospecting will expand the knowledge base of ligninolytic microbial communities, strains, and enzymes to facilitate the understanding of aromatics metabolism. Systems biology analyses achieve an understanding of molecular and systems-level degradation mechanisms and metabolic pathways of lignin and aromatics. By identifying these mechanisms, synthetic biology provides promising approaches to create the lignin conversion pathways and engineer ligninolytic strains suitable as potential hosts for lignin conversion. Techno-economic analysis of biological lignin upgrading to coproducts in biorefineries will guide the implementation of lignin valorization by mitigating technical risk for scale-up and improving the profitability of biorefinery. Through improving the understanding of biological lignin valorization, it should be possible to create biological lignin valorization route to effectively produce value-added products from lignin.« less

Converting lignocellulosics to simple sugars for second generation bioethanol is complicated due to biomass recalcitrance, and it requires a pretreatment stage prior to enzymatic hydrolysis. In this study, native, pretreated (acid and alkaline) and partially hydrolyzed poplar and switchgrass were characterized by using Simons’ staining for cellulose accessibility, GPC for degree of polymerization (DP), and FTIR for chemical structure of plant cell wall. The susceptibility of the pretreated biomass to enzymatic hydrolysis could not be easily predicted from differences in cellulose DP and accessibility. During hydrolysis, the most significant DP reduction occurred at the very beginning of hydrolysis, and themore » DP began to decrease at a significantly slower rate after this initial period, suggesting an existence of a synergistic action of endo- and exoglucanases that contribute to the occurrence of a “peeling off” mechanism. Cellulose accessibility was found to be increased at the beginning of hydrolysis, after reaching a maximum value then started to decrease. In conclusion, the fresh enzyme restart hydrolysis experiment along with the accessibility data indicated that the factors associated with the nature of enzyme such as irreversible nonspecific binding of cellulases by lignin and steric hindrance of enzymes should be responsible for the gradual slowing down of the reaction rate.« less

Metabolic synthesis of single cell oils (SCOs) for biodiesel application by heterotrophic oleaginous microorganisms is being hampered by the high cost of culture media. This study investigated the possibility of using loblolly pine and sweetgum autohydrolysates as economic feedstocks for microbial lipid production by oleaginous Rhodococcus opacus (R. opacus) PD630 and DSM 1069. Results revealed that when the substrates were detoxified by the removal of inhibitors (such as HMF—hydroxymethyl-furfural), the two strains exhibited viable growth patterns after a short adaptation/lag phase. R. opacus PD630 accumulated as much as 28.6 % of its cell dry weight (CDW) in lipids while growingmore » on detoxified sweetgum autohydrolysate (DSAH) that translates to 0.25 g/l lipid yield. The accumulation of SCOs reached the level of oleagenicity in DSM 1069 cells (28.3 % of CDW) as well, while being cultured on detoxified pine autohydrolysate (DPAH), with the maximum lipid yield of 0.31 g/l. The composition of the obtained microbial oils varied depending on the substrates provided. These results indicate that lignocellulosic autohydrolysates can be used as low-cost fermentation substrates for microbial lipid production by wild-type R. opacus species. Furthermore, the variety of applications for aqueous liquors from lignocellulosic pretreatment has been expanded, allowing for the further optimization of the integrated biorefinery.« less