Omega-3 fatty acids, and specifically docosahexaenoic acid (DHA), are important and essential nutrients for human health. thraustochytrids are recognised as commercial strains for nutraceuticals production, they are group of marine oleaginous microorganisms capable of co-synthesis of DHA and other valuable carotenoids in their cellular compartment. the present study sought to optimize DHA and squalene production by the thraustochytrid Schizochytrium limacinum SR21. The highest biomass yield (0.46 g/g substrate) and lipid productivity (0.239 g/g substrate) were observed with 60 g/L of glucose, following cultivation in a bioreactor, with the DHA content to be 67.76% w/w total lipids. to reduce costs, cheaper feedstocks and simultaneous production of various value-added products for pharmaceutical or energy use should be attempted. To this end, we replaced pure glucose with organosolv-pretreated spruce hydrolysate and assessed the simultaneous production of DHA and squalene from S. limacinum SR21. After the 72 h of cultivation period in bioreactor, the maximum DHA content was observed to 66.72% w/w total lipids that was corresponded to 10.15 g/L of DHA concentration. While the highest DHA productivity was 3.38 ± 0.27 g/L/d and squalene reached a total of 933.72 ± 6.53 mg/L (16.34 ± 1.81 mg/ g CDW). In summary, we show that the co-production of DHA and squalene makes S. limacinum SR21 appropriate strain for commercial-scale production of nutraceuticals. Omega-6 (n-6) and omega-3 (n-3) are polyunsaturated fatty acids (PUFAs), whose precursors include linoleic acid and alpha-linolenic acid. They are considered essential because humans cannot synthesize them due to insufficient levels of elongases and delta-6-desaturases 1,2. Although conversion of alpha-linolenic acid into omega-3 fatty acids, such as eicosapentaenoic acid (C 20:5n−3), docosapentaenoic acid (C 22:5n−3), and docosahexaenoic acid (C 22:6n−3 , DHA) occurs in humans, it happens at a very slow rate 3 and so these fatty acids must be provided by the diet. These PUFAs have several health benefits and have been found to be very effective in the preventions and treatment of fetal diseases 4. DHA plays a major role in cell signalling and is found mainly in the brain and retina tissues 5. Additionally, it acts as an anti-inflammatory agent, a precursor of several metabolites and potent lipid mediators, and could be used to treat several cardiovascular or neurologic disorders, such as hypertension and Alzheimer's 6. Fish of the Salmonidae, Scombridae, and Clupeidae families have been the sole commercial source of DHA as their oil contains approximately 20 to 30% DHA 3. However, DHA purification and concentration from fish oil is costly and the resulting oil quality depends on species, location, and pollution 7. Furthermore, fish-derived DHA is unsuitable for vegetarians, and diminishing fish stocks together with marine pollution limit the increasing demand for DHA 7. Oils from genetically engineered plant oilseeds, such as Brassica juncea, Arabidopsis thaliana, an...

One of the major challenges for the present and future generations is to find suitable substitutes for the fossil resources we rely on today. In this context, cyanobacterial carbohydrates have been discussed as an emerging renewable feedstock in industrial biotechnology for the production of fuels and chemicals. Based on this, we recently presented a synthetic bacterial co-culture for the production of medium-chain-length polyhydroxyalkanoates (PHAs) from CO 2 . This co-cultivation system is composed of two partner strains: Synechococcus elongatus cscB which fixes CO 2 , converts it to sucrose and exports it into the culture supernatant, and a Pseudomonas putida strain that metabolizes this sugar and accumulates PHAs in the cytoplasm. However, these biopolymers are preferably accumulated under conditions of nitrogen limitation, a situation difficult to achieve in a co-culture as the other partner, at best, should not perceive any limitation. In this article, we will present an approach to overcome this dilemma by uncoupling the PHA production from the presence of nitrate in the medium. This is achieved by the construction of a P. putida strain that is no longer able to grow with nitrate as nitrogen source -is thus nitrate blind, and able to grow with sucrose as carbon source. The deletion of the nasT gene encoding the response regulator of the NasS/NasT two-component system resulted in such a strain that has lost the ability use nitrate, but growth with ammonium was not affected. Subsequently, the nasT deletion was implemented in P. putida cscRABY, an efficient sucrose consuming strain. This genetic engineering approach introduced an artificial unilateral nitrogen limitation in the co-cultivation process, and the amount of PHA produced from light and CO 2 was 8.8 fold increased to 14.8% of its CDW compared to the nitrate consuming reference strain. This nitrate blind strain, P. putida nasT attTn7:cscRABY, is not only a valuable partner in the co-cultivation but additionally enables the use of other nitrate containing substrates for medium-chain-length PHA production, like for example waste-water.