title: Superior triacylglycerol (TAG) accumulation in starchless mutants of Scenedesmus obliquus: (I) mutant generation and characterization.
abstract: BACKGROUND
  Microalgae are a promising platform for producing neutral lipids, to be used in the application for biofuels or commodities in the feed and food industry. A very promising candidate is the oleaginous green microalga Scenedesmus obliquus, because it accumulates up to 45% w/w triacylglycerol (TAG) under nitrogen starvation. Under these conditions, starch is accumulated as well. Starch can amount up to 38% w/w under nitrogen starvation, which is a substantial part of the total carbon captured. When aiming for optimized TAG production, blocking the formation of starch could potentially increase carbon allocation towards TAG. In an attempt to increase TAG content, productivity and yield, starchless mutants of this high potential strain were generated using UV mutagenesis. Previous studies in Chlamydomonas reinhardtii have shown that blocking the starch synthesis yields higher TAG contents, although these TAG contents do not surpass those of oleaginous microalgae yet. So far no starchless mutants in oleaginous green microalgae have been isolated that result in higher TAG productivities.
  
  
  RESULTS
  Five starchless mutants have been isolated successfully from over 3,500 mutants. The effect of the mutation on biomass and total fatty acid (TFA) and TAG productivity under nitrogen-replete and nitrogen-depleted conditions was studied. All five starchless mutants showed a decreased or completely absent starch content. In parallel, an increased TAG accumulation rate was observed for the starchless mutants and no substantial decrease in biomass productivity was perceived. The most promising mutant showed an increase in TFA productivity of 41% at 4 days after nitrogen depletion, reached a TAG content of 49.4% (% of dry weight) and had no substantial change in biomass productivity compared to the wild type.
  
  
  CONCLUSIONS
  The improved S. obliquus TAG production strains are the first starchless mutants in an oleaginous green microalga that show enhanced TAG content under photoautotrophic conditions. These results can pave the way towards a more feasible microalgae-driven TAG production platform.
authors.affiliation: Bioprocess Engineering and AlgaePARC, Wageningen University and Research Centre, PO Box 8129, 6700 EV Wageningen, The Netherlands ; Food and Biobased Research and AlgaePARC, Wageningen University and Research Centre, PO Box 17, 6700 AA Wageningen, The Netherlands.
authors.forename: Lenny
authors.initials: L
authors.lastname: de Jaeger
authors.affiliation: Bioprocess Engineering and AlgaePARC, Wageningen University and Research Centre, PO Box 8129, 6700 EV Wageningen, The Netherlands.
authors.forename: Ruben Em
authors.initials: RE
authors.lastname: Verbeek
authors.affiliation: Unilever Research and Development Vlaardingen, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands.
authors.forename: René B
authors.initials: RB
authors.lastname: Draaisma
authors.affiliation: Bioprocess Engineering and AlgaePARC, Wageningen University and Research Centre, PO Box 8129, 6700 EV Wageningen, The Netherlands.
authors.forename: Dirk E
authors.initials: DE
authors.lastname: Martens
authors.affiliation: Food and Biobased Research and AlgaePARC, Wageningen University and Research Centre, PO Box 17, 6700 AA Wageningen, The Netherlands.
authors.forename: Jan
authors.initials: J
authors.lastname: Springer
authors.affiliation: Bioprocess Engineering and AlgaePARC, Wageningen University and Research Centre, PO Box 8129, 6700 EV Wageningen, The Netherlands ; Food and Biobased Research and AlgaePARC, Wageningen University and Research Centre, PO Box 17, 6700 AA Wageningen, The Netherlands.
authors.forename: Gerrit
authors.initials: G
authors.lastname: Eggink
authors.affiliation: Bioprocess Engineering and AlgaePARC, Wageningen University and Research Centre, PO Box 8129, 6700 EV Wageningen, The Netherlands.
authors.forename: René H
authors.initials: RH
authors.lastname: Wijffels
keywords: Acutodesmus obliquus; Biofuel; Metabolism; Scenedesmus obliquus; Starch; Starchless mutant; Triacylglycerol (TAG)