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Even with particular interest in sustainable development, due to the limited types of bioavailable carbon sources that could support heterotrophic/mixotrophic growth, microalgae-derived products still suffer from inconsistent yield and high costs. This study demonstrates a successful cocultivation of the photoautotroph Chlorella vulgaris with a hydrolytic-enzyme-abundant heterotroph, Saccharomycopsis fibuligera, enabling efficient starch upcycling from water/wastewater toward enhancing microalgae-dominant biomass and lipid production. The enzymatic activities of S. fibuligera contributed to the hydrolysis of starch into glucose, generating a 7-fold higher biomass through mixotrophic/heterotrophic growth of C. vulgaris. Further, scanning transmission electron microscopy (STEM) and quantitative analysis suggested a significantly induced accumulation of lipids in C. vulgaris. Results of meta-transcriptomics revealed the critical regulatory role of illumination in interaction shifting. Gene expression for glycolysis and lipid biosynthesis of C. vulgaris were highly activated during dark periods. Meanwhile, during illumination periods, genes coding for glucoamylase and the sulfur-related activities in S. fibuligera were significantly upregulated, leading to induced starch hydrolysis and potential increased competition for sulfur utilization, respectively. This study indicates that hydrolytic organisms could collaborate to make starch bioavailable for nonhydrolytic microalgae, thus broadening the substrate spectrum and making starch a novel biotechnological feedstock for microalgae-derived products, e.g., biofuels or single-cell protein.

Astaxanthin is a valuable carotenoid pigment, which has been extensively used in various industries. In this study, Rhodosporidium toruloides was first used as a new microbial source for producing natural astaxanthin. Various carbon, nitrogen, and mineral sources were evaluated for their effect on astaxanthin production of R. toruloides. Response surface methodology (RSM) was then used to optimize the medium compositions for maximizing the astaxanthin concentration. Among the examined nutrients, glucose, peptone, and KH2PO4 were the most efficient carbon, nitrogen, and mineral source for astaxanthin production, respectively. Through RSM, a maximum astaxanthin concentration of 927.11 µg l-1 was obtained by using Hansen broth containing 83.74 g l-1 glucose, 20.01 g l-1 peptone, and 6.19 g l-1 KH2PO4. This study suggested that R. toruloides is a promising candidate to produce natural astaxanthin.

The microalga Nannochloropsis gaditana is a natural producer of triacylglycerol (TAG) and the omega-3 fatty acid eicosapentaenoic acid (EPA). TAG accumulation is induced by nitrogen starvation. The biomass-specific photon supply rate used had an effect on EPA and TAG accumulation during nitrogen starvation as well as on the localization of EPA accumulation. Clear differences in TAG yield on light were found for different biomass-specific photon supply rates and light regimes during nitrogen starvation. De novo EPA synthesis or the translocation of EPA between lipid fractions might be limiting for EPA accumulation in TAG. Further studies are needed to fully understand EPA accumulation in TAG during nitrogen starvation. To elucidate the function of EPA in TAG nitrogen recovery, experiments are suggested. The overexpression of genes involved in de novo EPA synthesis and translocation is proposed to elucidate the exact metabolic routes involved in these processes during nitrogen starvation. This work addresses future opportunities to increase EPA accumulation.

Cocoa butter (CB) extracted from cocoa beans is the main raw material for chocolate production. However, growing chocolate demands and limited CB production has resulted in a shortage of CB supply. CB is mainly composed of three different kinds of triacylglycerols (TAGs), POP (C16:0–C18:1–C16:0), POS (C16:0–C18:1–C18:0), and SOS (C18:0–C18:1–C18:0). The storage lipids of yeasts, mainly TAGs, also contain relative high-level of C16 and C18 fatty acids and might be used as CB-like lipids (CBL). In this study, we cultivated six different yeasts, including one non-oleaginous yeast strain, Saccharomyces cerevisiae CEN.PK113-7D, and five oleaginous yeast strains, Trichosporon oleaginosus DSM11815, Rhodotorula graminis DSM 27356, Lipomyces starkeyi DSM 70296, Rhodosporidium toruloides DSM 70398, and Yarrowia lipolytica CBS 6124, in nitrogen-limited medium and compared their CBL production ability. Under the same growth conditions, we found that TAGs were the main lipids in all six yeasts and that T. oleaginosus can produce more TAGs than the other five yeasts. Less than 3% of the total TAGs were identified as potential SOS in the six yeasts. However, T. oleaginosus produced 27.8% potential POP and POS at levels of 378 mg TAGs/g dry cell weight, hinting that this yeast may have potential as a CBL production host after further metabolic engineering in future.

The development of clean, sustainable alternative energy sources is increasingly important. One promising alternative to depleting fuel reserves is algae-based biodiesel fuel, which is both non-toxic and renewable. Despite the tremendous potential of algae-based biodiesel fuel, it has not yet been profitable because of the high cost per unit area of large cultivation. We present a novel application of Orthogonal Array Composite Designs (OACDs) to optimize lipid production of a cell-free system for algae. An OACD consists of a two-level fractional factorial design and a three-level orthogonal array. We start with an initial screening experiment based on six chemicals using an OACD with 50 runs. Based on this experiment, two chemical compounds were removed and a follow-up 25-run OACD with four chemicals was performed. Our analysis shows that only three chemicals – nitrogen, magnesium, and phosphate – are essential for lipid accumulation, and a range of optimum combinations of these three chemicals is identified. The lipid accumulation for these three chemical combinations is substantially higher in comparison to the commercial medium, which contains 16 chemicals and soil water. This leads to a reduced cost of the chemical medium and increased efficiency of biodiesel production from the algal-based cell-free system, which can be used to significantly expand the use of biodiesel as a viable alternative to fossil fuels. Copyright © 2015 John Wiley & Sons, Ltd.

The development of clean, sustainable alternative energy sources is increasingly important. One promising alternative to depleting fuel reserves is algae-based biodiesel fuel, which is both non-toxic and renewable. Despite the tremendous potential of algae-based biodiesel fuel, it has not yet been profitable because of the high cost per unit area of large cultivation. We present a novel application of Orthogonal Array Composite Designs (OACDs) to optimize lipid production of a cell-free system for algae. An OACD consists of a two-level fractional factorial design and a three-level orthogonal array. We start with an initial screening experiment based on six chemicals using an OACD with 50 runs. Based on this experiment, two chemical compounds were removed and a follow-up 25-run OACD with four chemicals was performed. Our analysis shows that only three chemicals – nitrogen, magnesium, and phosphate – are essential for lipid accumulation, and a range of optimum combinations of these three chemicals is identified. The lipid accumulation for these three chemical combinations is substantially higher in comparison to the commercial medium, which contains 16 chemicals and soil water. This leads to a reduced cost of the chemical medium and increased efficiency of biodiesel production from the algal-based cell-free system, which can be used to significantly expand the use of biodiesel as a viable alternative to fossil fuels. Copyright © 2015 John Wiley & Sons, Ltd.

Le biodiesel s’affirme comme une alternative à l’utilisation des carburants fossiles surtout parce qu’il est renouvelable, biodégradable, non toxique et non dommageable à l’environnement. Parallèlement, la gestion des déchets solides à Québec s’avère être une préoccupation majeure. Notre étude s’est donc focalisée sur la production de lipides pour leur conversion en biodiesel en utilisant un substrat à moindre coût tel que les boues d’épuration secondaires qui ont été collectées à la station d’épuration de la Communauté Urbaine de Québec (CUQ). Pour ce faire, différents types de boues (les boues lavées, non-lavées et centrifugées) ont été utilisées avec des concentrations en solides en suspension variant de 30 à 40 g/l pour la production de lipides par Trichosporon Oleaginosus. De plus dépendamment des cas, du glycérol brut purifié a été ajouté afin d’accroître cette production. Les résultats obtenus, à l’issu de ce travail ont montré que lorsque les boues sont lavées, elles permettent une meilleure accumulation de lipides. Mieux, l’impact de la variation des matières en suspension fut investigué et a montré qu’à une concentration en matières en suspension de 35 g/l plus 40 g/l de glycérol avec ces mêmes boues lavées, une concentration de 20,4 g/l de lipides est obtenue. De plus, la mesure des paramètres tels que l’OUR, l’OTR et le KLa a confirmé la performance du bioréacteur lorsqu’il est opéré sous ces conditions. Biodiesel is emerging as a favourable alternative to the fossil fuel extinctions since it is renewable, biodegradable, non-toxic and eco-friendly environment. Meanwhile, wastes management in Québec is proving to be a major concern. Then, our study is focused on lipid production for biodiesel conversion by using a lower cost substrate such as secondary wastewater sludge collected from the wastewater treatment plant of the Urban Community Québec (CUQ). Thus, to achieve this, different types of sludge such as washed sludge, unwashed and centrif

Background: Oleaginous yeast species are an alternative for the production of lipids or triacylglycerides (TAGs). These yeasts are usually non-pathogenic and able to store TAGs ranging from 20 % to 70 % of their cell mass depending on culture conditions. TAGs originating from oleaginous yeasts can be used as the so-called second generation biofuels, which are based on non-food competing "waste carbon sources". Results: In this study the selection of potentially new interesting oleaginous yeast strains is described. Important selection criteria were: a broad maximum temperature and pH range for growth (robustness of the strain), a broad spectrum of carbon sources that can be metabolized (preferably including C-5 sugars), a high total fatty acid content in combination with a low glycogen content and genetic accessibility. Conclusions: Based on these selection criteria, among 24 screened species, Schwanniomyces occidentalis (Debaromyces occidentalis) CBS2864 was selected as a promising strain for the production of high amounts of lipids.

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.