title: Genetic and nutrient modulation of acetyl-CoA levels in Synechocystis for n-butanol production.
abstract: BACKGROUND
  There is a strong interest in using photosynthetic cyanobacteria as production hosts for biofuels and chemicals. Recent work has shown the benefit of pathway engineering, enzyme tolerance, and co-factor usage for improving yields of fermentation products.
  
  
  RESULTS
  An n-butanol pathway was inserted into a Synechocystis mutant deficient in polyhydroxybutyrate synthesis. We found that nitrogen starvation increased specific butanol productivity up to threefold, but cessation of cell growth limited total n-butanol titers. Metabolite profiling showed that acetyl-CoA increased twofold during nitrogen starvation. Introduction of a phosphoketolase increased acetyl-CoA levels sixfold at nitrogen replete conditions and increased butanol titers from 22 to 37 mg/L at day 8. Flux balance analysis of photoautotrophic metabolism showed that a Calvin-Benson-Bassham-Phosphoketolase pathway had higher theoretical butanol productivity than CBB-Embden-Meyerhof-Parnas and a reduced butanol ATP demand.
  
  
  CONCLUSIONS
  These results demonstrate that phosphoketolase overexpression and modulation of nitrogen levels are two attractive routes toward increased production of acetyl-CoA derived products in cyanobacteria and could be implemented with complementary metabolic engineering strategies.
authors.affiliation: School of Biotechnology, KTH, Royal Institute of Technology, Science for Life Laboratory, Stockholm, Sweden. janfelt@kth.se.
authors.forename: Josefine
authors.initials: J
authors.lastname: Anfelt
authors.affiliation: School of Biotechnology, KTH, Royal Institute of Technology, Science for Life Laboratory, Stockholm, Sweden. danutak@kth.se.
authors.forename: Danuta
authors.initials: D
authors.lastname: Kaczmarzyk
authors.affiliation: School of Biotechnology, KTH, Royal Institute of Technology, Science for Life Laboratory, Stockholm, Sweden. kiyan@kth.se.
authors.forename: Kiyan
authors.initials: K
authors.lastname: Shabestary
authors.affiliation: School of Biotechnology, KTH, Royal Institute of Technology, Science for Life Laboratory, Stockholm, Sweden. bjorn.renberg@biotech.kth.se.
authors.forename: Björn
authors.initials: B
authors.lastname: Renberg
authors.affiliation: School of Biotechnology, KTH, Royal Institute of Technology, Science for Life Laboratory, Stockholm, Sweden. johan.rockberg@biotech.kth.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Rockberg
authors.affiliation: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Hørsholm, Denmark. nielsenj@chalmers.se.|Department of Chemical and Biological Engineering, Chalmers Institute of Technology, Gothenburg, Sweden. nielsenj@chalmers.se.
authors.forename: Jens
authors.initials: J
authors.lastname: Nielsen
authors.affiliation: School of Biotechnology, KTH, Royal Institute of Technology, Science for Life Laboratory, Stockholm, Sweden. mathias.uhlen@scilifelab.se.|Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Hørsholm, Denmark. mathias.uhlen@scilifelab.se.
authors.forename: Mathias
authors.initials: M
authors.lastname: Uhlén
authors.affiliation: School of Biotechnology, KTH, Royal Institute of Technology, Science for Life Laboratory, Stockholm, Sweden. huds@kth.se.
authors.forename: Elton P
authors.initials: EP
authors.lastname: Hudson
mesh_terms: D020001:1-Butanol / Q000737:chemistry / Q000378:metabolism*; D000105:Acetyl Coenzyme A / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000446:Aldehyde-Lyases / Q000235:genetics / Q000378:metabolism; D018533:Biomass; D060847:Metabolic Engineering; D055442:Metabolome; D009243:NAD / Q000737:chemistry / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D046939:Synechocystis / Q000378:metabolism*
chemical_list: D009243:NAD; D000105:Acetyl Coenzyme A; D000255:Adenosine Triphosphate; D020001:1-Butanol; D000446:Aldehyde-Lyases; C022367:phosphoketolase; D009584:Nitrogen