Abstract
Global energy demands and global warming represent key challenges of the future of human society. Continous renewable energy supply is key for sustainable economy development. Waste plant biomass represent abundant source of renewable energy that can be transformed to biofuels and other value-added products, which is currently limited due to the lack of cost-effective biocatalysts. The bottleneck of this process is the degradation of structural polysaccharides of plant cell walls to soluble compounds that can be fermented to solvents or transformed to biogas via methanogenesis and can be used as biofuels or chemical raw materials. In order to replace traditional physical and chemical methods of lignocellulose pretreatment with more environmentally friendly biological approaches, native microbial enzyme systems are increasingly being explored as potential biocatalysts that could be used in these processes. Microbial enzymes are useful either as catalysts in the enzymatic hydrolysis of lignocelluloses or as components incorporated in engineered microbes for consolidated bioprocessing of lignocelluloses. The unprecedented development of tools for genetic and metabolic engineering for a wide range of microorganisms enabled significant progress in the development of microbial cell factories optimized for the producton of biofuels. One of the most promising strategies aimed towards this goal, i.e. systematic design and heterologous expression of »designer cellulosomes« in industrial solventogenic strains is adressed in detail.
Highlights
Global society is confronted with climate change, which is frequently associated with excessive consumption of fossil fuels, currently the most important source of energy on the planet
One of the main strategies striving towards more efficient conversion of lignocellulose to biofuels is the development of consolidated bioprocesses
Microbial cell factory design is an approach to bioengineering which considers microbial cells as a production facility in which the optimization process largely depends on metabolic engineering
Summary
Global society is confronted with climate change, which is frequently associated with excessive consumption of fossil fuels, currently the most important source of energy on the planet. The biggest bottleneck in the production of these, so-called second generation biofuels, is the conversion of the lignocellulosic biomass into soluble compounds that could be fermented to biofuels or other bio-based raw materials (chemicals and industrially-relevant enzymes). This step is enzymatically demanding and cannot be performed by most of the naturally solventogenic strains used in industrial processes. To facilitate the degradation of lignocellulose to fermentable compounds, pretreatment with concentrated chemicals (acids, bases, organic solvents or oxidants) and/or physical pretreatments (treatment with hot steam under pressure, pyrolysis, ultrasonic treatment) has traditionally been used Such procedures are associated with environmental and cost burden (Chen et al, 2017). This review is focused on important scientific findings in the field of microbial enzyme systems for the degradation of lignocellulosic biomass and selected results of metabolic engineering experiments to design microbial cell factories for the production of second generation biofuels
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