title: Heterologous expression of the mevalonic acid pathway in cyanobacteria enhances endogenous carbon partitioning to isoprene.
abstract: Heterologous expression of the isoprene synthase gene in the cyanobacterium Synechocystis PCC 6803 conferred upon these microorganisms the property of photosynthetic isoprene (C₅H₈) hydrocarbons production. Continuous production of isoprene from CO₂ and H₂O was achieved in the light, occurring via the endogenous methylerythritol-phosphate (MEP) pathway, in tandem with the growth of Synechocystis. This work addressed the issue of photosynthetic carbon partitioning between isoprene and biomass in Synechocystis. Evidence is presented to show heterologous genomic integration and cellular expression of the mevalonic acid (MVA) pathway genes in Synechocystis endowing a non-native pathway for carbon flux amplification to isopentenyl-diphosphate (IPP) and dimethylallyl-diphosphate (DMAPP) precursors of isoprene. Heterologous expression of the isoprene synthase in combination with the MVA pathway enzymes resulted in photosynthetic isoprene yield improvement by approximately 2.5-fold, compared with that measured in cyanobacteria transformed with the isoprene synthase gene only. These results suggest that the MVA pathway introduces a bypass in the flux of endogenous cellular substrate in Synechocystis to IPP and DMAPP, overcoming flux limitations of the native MEP pathway. The work employed a novel chromosomal integration and expression of synthetic gene operons in Synechocystis, comprising up to four genes under the control of a single promoter, and expressing three operons simultaneously. This is the first time an entire biosynthetic pathway with seven recombinant enzymes has been heterologously expressed in a photosynthetic microorganism. It constitutes contribution to the genetic engineering toolkit of photosynthetic microorganisms and a paradigm in the pursuit of photosynthetic approaches for the renewable generation of high-impact products.
authors.affiliation: Department of Plant and Microbial Biology, University of California, 111 Koshland Hall, Berkeley, CA 94720-3102, USA.
authors.forename: Fiona K
authors.initials: FK
authors.lastname: Bentley
authors.forename: Andreas
authors.initials: A
authors.lastname: Zurbriggen
authors.forename: Anastasios
authors.initials: A
authors.lastname: Melis
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D002070:Butadienes; D004269:DNA, Bacterial / Q000235:genetics; D017353:Gene Deletion; D015870:Gene Expression; D006006:Glycogen Synthase / Q000172:deficiency / Q000235:genetics; D045782:Hemiterpenes / Q000096:biosynthesis*; D007517:Isoamylase / Q000172:deficiency / Q000235:genetics; D008798:Mevalonic Acid / Q000378:metabolism*; D010420:Pentanes; D010788:Photosynthesis; D046939:Synechocystis / Q000235:genetics* / Q000378:metabolism*; D014170:Transformation, Genetic; D019076:Transgenes / Q000235:genetics
chemical_list: D002070:Butadienes; D004269:DNA, Bacterial; D045782:Hemiterpenes; D010420:Pentanes; C005059:isoprene; D006006:Glycogen Synthase; D019883:Alkyl and Aryl Transferases; C093854:isoprene synthase; D007517:Isoamylase; D008798:Mevalonic Acid
keywords: Synechocystis; biofuels; cyanobacteria; isoprene; isoprene synthase; metabolic engineering; photosynthesis