Role of Escherichia coli in Biofuel Production

Increased energy consumption coupled with depleting petroleum reserves and increased greenhouse gas emissions have renewed our interest in generating fuels from renewable energy sources via microbial fermentation. Central to this problem is the choice of microorganism that catalyzes the production of fuels at high volumetric productivity and yield from cheap and abundantly available renewable energy sources. Microorganisms that are metabolically engineered to redirect renewable carbon sources into desired fuel products are contemplated as best choices to obtain high volumetric productivity and yield. Considering the availability of vast knowledge in genomic and metabolic fronts, Escherichia coli is regarded as a primary choice for the production of biofuels. Here, we reviewed the microbial production of liquid biofuels that have the potential to be used either alone or in combination with the present-day fuels. We specifically highlighted the metabolic engineering and synthetic biology approaches used to improve the production of biofuels from E. coli over the past few years. We also discussed the challenges that still exist for the biofuel production from E. coli and their possible solutions.

Comparing soluble Trametes pubescens laccase and cross-linked enzyme crystals (CLECs) for enzymatic modification of cellulose 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Three types of preparations – enzyme immobilized on Eupergit C, cross-linked enzyme crystals (CLECs) and lyophilized enzyme – have been obtained from Trametes pubescens laccase. Their activity in organic solvents has been comparatively evaluated, whereby the CLECs showed a significantly higher activity compared to the immobilized and the lyophilized variant. The soluble, lyophilized laccase and the CLECs were compared for their activity in the oxidation of cellulose in the laccase/TEMPO system. The “double heterogeneous” CLEC system – both the CLECs and the cellulose substrates are solids and only the mediator is homogeneously dissolved – showed similar reactivity to the conventional enzyme system. Laccase CLECs, being a solid, robust and highly active immobilized enzyme form can be conveniently used to modify (protected) low-molecular weight carbohydrates or cellulosics also in (aqueous-)organic media, and they offer many practical advantages: operational stability and ease of recycling coupled with high volumetric productivity.