title: Superior triacylglycerol (TAG) accumulation in starchless mutants of Scenedesmus obliquus: (II) evaluation of TAG yield and productivity in controlled photobioreactors.
abstract: BACKGROUND
  Many microalgae accumulate carbohydrates simultaneously with triacylglycerol (TAG) upon nitrogen starvation, and these products compete for photosynthetic products and metabolites from the central carbon metabolism. As shown for starchless mutants of the non-oleaginous model alga Chlamydomonas reinhardtii, reduced carbohydrate synthesis can enhance TAG production. However, these mutants still have a lower TAG productivity than wild-type oleaginous microalgae. Recently, several starchless mutants of the oleaginous microalga Scenedesmus obliquus were obtained which showed improved TAG content and productivity.
  
  
  RESULTS
  The most promising mutant, slm1, is compared in detail to wild-type S. obliquus in controlled photobioreactors. In the slm1 mutant, the maximum TAG content increased to 57 ± 0.2% of dry weight versus 45 ± 1% in the wild type. In the wild type, TAG and starch were accumulated simultaneously during initial nitrogen starvation, and starch was subsequently degraded and likely converted into TAG. The starchless mutant did not produce starch and the liberated photosynthetic capacity was directed towards TAG synthesis. This increased the maximum yield of TAG on light by 51%, from 0.144 ± 0.004 in the wild type to 0.217 ± 0.011 g TAG/mol photon in the slm1 mutant. No differences in photosynthetic efficiency between the slm1 mutant and the wild type were observed, indicating that the mutation specifically altered carbon partitioning while leaving the photosynthetic capacity unaffected.
  
  
  CONCLUSIONS
  The yield of TAG on light can be improved by 51% by using the slm1 starchless mutant of S. obliquus, and a similar improvement seems realistic for the areal productivity in outdoor cultivation. The photosynthetic performance is not negatively affected in the slm1 and the main difference with the wild type is an improved carbon partitioning towards TAG.
authors.affiliation: Bioprocess Engineering & AlgaePARC, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, Netherlands.
authors.forename: Guido
authors.initials: G
authors.lastname: Breuer
authors.affiliation: Bioprocess Engineering & AlgaePARC, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, Netherlands.|Food and Biobased Research & AlgaePARC, Wageningen University and Research Centre, P.O. Box 17, 6700 AA Wageningen, Netherlands.
authors.forename: Lenny
authors.initials: L
authors.lastname: de Jaeger
authors.affiliation: Bioprocess Engineering & AlgaePARC, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, Netherlands.
authors.forename: Valentin P G
authors.initials: VPG
authors.lastname: Artus
authors.affiliation: Bioprocess Engineering & AlgaePARC, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, Netherlands.
authors.forename: Dirk E
authors.initials: DE
authors.lastname: Martens
authors.affiliation: Food and Biobased Research & AlgaePARC, Wageningen University and Research Centre, P.O. Box 17, 6700 AA Wageningen, Netherlands.
authors.forename: Jan
authors.initials: J
authors.lastname: Springer
authors.affiliation: Unilever Research and Development Vlaardingen, Olivier van Noortlaan 120, 3133 AT Vlaardingen, Netherlands.
authors.forename: René B
authors.initials: RB
authors.lastname: Draaisma
authors.affiliation: Bioprocess Engineering & AlgaePARC, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, Netherlands.|Food and Biobased Research & AlgaePARC, Wageningen University and Research Centre, P.O. Box 17, 6700 AA Wageningen, Netherlands.
authors.forename: Gerrit
authors.initials: G
authors.lastname: Eggink
authors.affiliation: Bioprocess Engineering & AlgaePARC, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, Netherlands.
authors.forename: René H
authors.initials: RH
authors.lastname: Wijffels
authors.affiliation: Bioprocess Engineering & AlgaePARC, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, Netherlands.
authors.forename: Packo P
authors.initials: PP
authors.lastname: Lamers
keywords: Acutodesmus obliquus; Scenedesmus obliquus; mutant; starch; starchless; triacylglycerol (TAG)