Superior triacylglycerol (TAG) accumulation in starchless mutants of Scenedesmus obliquus: (II) evaluation of TAG yield and productivity in controlled photobioreactors

Abstract

BackgroundMany 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.ResultsThe 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.ConclusionsThe 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.

Isolation and Characterization of Native Microalgae from the Peruvian Amazon with Potential for Biodiesel Production

“…and total carbohydrate content (from 11.9% in Acutodesmus obliquus to 96.3% in Chlorella lewinii), but showed a decreased in total protein levels (from 24.2% in Acutodesmus obliquus to 54.5% in Chlorella lewinii) in comparison to +N cultures (Figure 3). These results are in accordance with well-documented results obtained by other researchers with several microalgae species of the genera Acutodesmus, Ankistrodesmus, Botryococcus, Chlamydomonas, Chlorella, Desmodesmus, Dunaliella, Haematococcus, Neochloris, Phaeodactylum, Pseudokirchneriella and Scenedesmus [46,50,58,59,64,[75][76][77][78][79][80]. Nevertheless, the accumulation of total lipid induced by nitrogen deficiency is not correlated with lipid productivity, but rather is due to a decline and stopping of the microalgae specific growth rate [75].…”

Photosynthetic efficiency and carbon partitioning in nitrogen-starved Scenedesmus obliquus

“…Furthermore, even in the best TAG producing microalgae species, TAG only accounts for approximately half of the biomass produced after the depletion of nitrogen [5]. Other biomass constituents, such as starch, are produced simultaneously [6]. The overall TAG productivity during nitrogen starvation is thus determined by the product of the photosynthetic rate during nitrogen starvation and the fraction thereof that is partitioned towards TAG synthesis.…”

The fatter the better : selecting microalgae cells for outdoor lipid production

“…We calculated the TAG yields on light of both original and S5 as being 0. 16 73 also presents the TAG yield of an starchless mutant of Scenedesmus obliquus at 0.37 g mol -1 , close to the yields measured for the S5 in the current work (0.32 g mol …”

“…high lipid producers) 10,72 . Another possibility is to increase genetic variability by inducing mutations in a parental population and screen and sort for mutants with abnormal improved features 9,14,21,73 . Fluorescence assisted cell sorting (FACS) is a method which allows rapid screening and sorting of cells with desired characteristics.…”