Hi-Solids

Lignocellulosic biomass (LC) represents the most promising renewable resource for a sustainable energy and chemical production. Nevertheless, LC is a complex structure which is difficult to transform. To improve LC transformation, so far, lot of research has been realized on selecting microbes producing lignocellulolytic enzyme, finding new enzymes or improving enzyme properties by molecular and meta-omics approaches, or improving processes for enzyme production. Similarly, a big effort was made to develop LC pretreatment processes. Despite such efforts, the major challenges of LC biorefinery are still the high cost of pretreatment and the low efficiency of LC enzymatic hydrolysis. In this context, Hi-Solids propose to adopt a holistic approach to devise an innovative dry biorefinery process that combines advanced pretreatment by Reactive-Extrusion with the action of microbial consortia to produce carboxylates from high solid loads of LC. Microbial communities display high diversity and metabolic versatility, which can be exploited to develop bioconversion processes for LC. The metabolism of microbial consortia can be directed towards the production of carboxylates. The production of carboxylates is of particular interest because they are intermediate building blocks for the production of chemicals, bioplastics and biofuels. To enhance carboxylate production from LC biomass, it is mandatory to devise new biomass pretreatment processes to increase LC accessibility. To achieve this, and to attain economic and environmental sustainability, the ideal pretreatment and bioconversion process should handle high solid loadings, while limiting the use of chemicals and energy. However, high solids loadings will inevitably impact microbial and enzymatic activities. Thus, Hi-Solids propose to assess the Reactive-Extrusion process as a means to deconstruct LC for further biological transformation by microbial consortia. Hi-Solids propose to combine specific enzymes with extrusion, notably targeting key structural features of the hemicellulosic and lignin fractions. The LC substrate that will be studied in Hi-Solids is corn stover because this substrate is not in competition with human or animal food consumption. The raw and pretreated LC will be submitted to extensive physico-chemical characterization in order to determine precisely the nature of the reactive-extrusion impacts. In order to enhance carboxylate production by microbial consortia, Hi-Solids will assess the effects of both pretreatment and high solid loads on the enzymatic activities and on the functional diversity of microbial consortia enriched from highly lignocellulolytic microbiomes. The functional assessment of microbial consortia will be carried-out by high-throughput metagenomic-metatranscriptomic approaches combined to macro-kinetics and mass transfer analysis in order to optimize the carboxylate production from LC at high solid loads. Thus, Hi-Solids will deliver both fundamental understanding of the processes that occur during enzyme-mediated reactive-extrusion of LC biomass and of its consequences on the metabolic activity of microbial consortia operating at high solid loadings. Accordingly, Hi-Solids will provide the underpinning knowledge for a significant innovation step which involves combining enzyme-coupled to extrusion with the power and robustness of microbial consortia to design a new biorefinery concept. In addition, the project will provide new knowledge that will facilitate the industrial implementation of LC conversion processes by microbial consortia at high solid loads for carboxylate production.