The production of isoprene from cellulose using recombinant Clostridium cellulolyticum strains expressing isoprene synthase

Isoprene is an important bulk chemical which is mostly derived from fossil fuels. It is used primarily for the production of synthetic rubber. Sustainable, biotechnology-based alternatives for the production of isoprene rely on the fermentation of sugars from food and feed crops, creating an ethical dilemma due to the competition for agricultural land. This issue could be addressed by developing new approaches based on the production of isoprene from abundant renewable waste streams. Here, we describe a proof-of-principle approach for the production of isoprene from cellulosic biomass, the most abundant polymer on earth. We engineered the mesophilic prokaryote Clostridium cellulolyticum, which can degrade cellulosic biomass, to utilize the resulting glucose monomers as a feedstock for the production of isoprene. This was achieved by integrating the poplar gene encoding isoprene synthase. The presence of the enzyme was confirmed by targeted proteomics, and the accumulation of isoprene was confirmed by GC-MS/MS. We have shown for the first time that engineered C. cellulolyticum can be used as a metabolic chassis for the sustainable production of isoprene.