Functional characterization and substrate specificity analysis of Δ6-desaturase from marine microalga Isochrysis sp

Solid-state fermentation produces greater stearidonic acid levels in genetically engineered Mucor circinelloides

Omega-3 (ω-3) polyunsaturated fatty acids (PUFAs) are important dietary components due to their health benefits and preventative role in cardiovascular disease. Fish-based and plant seed oils are rich in stearidonic acid (SDA; 18:4 n-3) which are readily metabolized into ω-3 PUFAs such as eicosapentaenoic acid. However, these natural sources of SDA are generally low yielding and are unlikely to meet global demands, so new sustainable microbial fermentative sources of SDA need to be identified. Expression of delta15-desaturase in the oleaginous filamentous fungus Mucor circinelloides (McD15D) has been used to construct a recombinant SDA-producing McD15D strain that produces 5.0% SDA levels using submerged fermentation conditions. Switching to solid-state fermentation conditions in the same medium with submerged fermentation resulted in this engineered strain producing significantly higher amounts of SDA. A Box-Behnken design (BBD) of response surface methodology (RSM) approach has been used to identify optimal glucose and ammonium tartrate concentrations and temperature levels to maximize SDA production. The use of these optimal solid-state fermentation conditions resulted in the spores and mycelium of the recombinant McD15D producing 19.5% (0.64 mg g^-1 ) and 12.2% (1.52 mg g^-1 ) SDA content respectively, which represents an overall increase in SDA yield of 188.0% when compared to SDA yields produced using submerged fermentation conditions.

Key Enzymes in Fatty Acid Synthesis Pathway for Bioactive Lipids Biosynthesis

Dietary bioactive lipids, one of the three primary nutrients, is not only essential for growth and provides nutrients and energy for life's activities but can also help to guard against disease, such as Alzheimer's and cardiovascular diseases, which further strengthen the immune system and maintain many body functions. Many microorganisms, such as yeast, algae, and marine fungi, have been widely developed for dietary bioactive lipids production. These biosynthetic processes were not limited by the climate and ground, which are also responsible for superiority of shorter periods and high conversion rate. However, the production process was also exposed to the challenges of low stability, concentration, and productivity, which was derived from the limited knowledge about the critical enzyme in the metabolic pathway. Fortunately, the development of enzymatic research methods provides powerful tools to understand the catalytic process, including site-specific mutagenesis, protein dynamic simulation, and metabolic engineering technology. Thus, we review the characteristics of critical desaturase and elongase involved in the fatty acids' synthesis metabolic pathway, which aims to not only provide extensive data for enzyme rational design and modification but also provides a more profound and comprehensive understanding of the dietary bioactive lipids' synthetic process.

Highly Valuable Polyunsaturated Fatty Acids from Microalgae: Strategies to Improve Their Yields and Their Potential Exploitation in Aquaculture

Microalgae have a great potential for the production of healthy food and feed supplements. Their ability to convert carbon into high-value compounds and to be cultured in large scale without interfering with crop cultivation makes these photosynthetic microorganisms promising for the sustainable production of lipids. In particular, microalgae represent an alternative source of polyunsaturated fatty acids (PUFAs), whose consumption is related to various health benefits for humans and animals. In recent years, several strategies to improve PUFAs' production in microalgae have been investigated. Such strategies include selecting the best performing species and strains and the optimization of culturing conditions, with special emphasis on the different cultivation systems and the effect of different abiotic factors on PUFAs' accumulation in microalgae. Moreover, developments and results obtained through the most modern genetic and metabolic engineering techniques are described, focusing on the strategies that lead to an increased lipid production or an altered PUFAs' profile. Additionally, we provide an overview of biotechnological applications of PUFAs derived from microalgae as safe and sustainable organisms, such as aquafeed and food ingredients, and of the main techniques (and their related issues) for PUFAs' extraction and purification from microalgal biomass.

Heterologous Production of Polyunsaturated Fatty Acids in E. coli Using Δ5-Desaturase Gene from Microalga Isochrysis Sp

Eicosapentaenoic acid (EPA) and arachidonic acid (ARA) are long-chain polyunsaturated fatty acids (PUFAs) that play a significant role in human growth and development, which deficiency can trigger several metabolic-related diseases. Since the availability of PUFA sources is limited, there arises a need to explore alternative sources. Therefore, the present study aimed to investigate whether an Escherichia coli which are engineered with Δ5Des-Iso gene isolated from Isochrysis sp. could be utilized to synthesize PUFAs. Full-length gene Δ5Des-Iso (1149 bp) was isolated from Isochrysis sp. that encodes 382 amino acids and identified as Δ5-desatruase gene using different bioinformatic analysis. Heterologous gene expression was carried out in E. coli having Δ5Des-Iso with precursor fatty acids. The Δ5Des-Iso produced novel fatty acids of EPA (ω-3) and ARA (ω-6) as respective products were identified by GC-MS. Gene expression and PUFA synthesis in E. coli were optimized by temperature, time, and concentrations of precursor fatty acid substrates. Δ5Des-Iso RNA transcript level was inversely proportional to the time and fatty acid synthesis. And, the significant production of EPA (4.1 mg/g) and ARA (8.3 mg/g) in total fatty acids was observed in E. coli grown at 37 °C for 24 h with 25 μM of external fatty acid substrate as an optimum growth conditions. E. coli could be used as alternative organism to synthesis PUFAs and widely applicable in many nutraceuticals and pharmaceuticals industry for human use.

Δ6 fatty acid desaturases in polyunsaturated fatty acid biosynthesis: insights into the evolution, function with substrate specificities and biotechnological use

Δ6 fatty acid desaturases (FADS6) have different substrate specificities that impact the ratio of omega-6/omega-3 polyunsaturated fatty acids, which are involved in regulating multiple signalling pathways associated with various diseases. For decades, FADS6 with different substrate specificities have been characterized and the functions of these crucial enzymes have been investigated, while it remains enigmatic that the substrate specificities of FADS6 from various species have a huge difference. This review summarizes the substrate specificities of FADS6 in different species and reveals the underlying relationship. Further evaluation of biochemical properties has revealed that the FADS6 prefer linoleic acid that is more hydrophilic and stable. Domain-swapping and site-directed mutagenesis have been employed to delineate the regions and sites that affect the substrate specificities of FADS6. These analyses improve our understanding of the functions of FADS6 and offer information for the discovery of novel biological resources. KEY POINTS: • Outline of the excavation and identification of Δ6 fatty acid desaturases. • Overview of methods used to determine the pivotal resides of desaturases. • Application of substrate properties to generate specific fatty acids.

Lowering the culture medium temperature improves the omega-3 fatty acid production in marine microalga Isochrysis sp. CASA CC 101

Marine microalga Isochrysis sp. contains omega-3 fatty acids like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Environmental factors play a major role in PUFA biosynthesis. Hence, the study focused to optimize factors such as temperature, pH, and photoperiod by response surface methodology (RSM). RSM results showed that the model is significant (p ≤ 0.05) with a high correlation coefficient (R² = 0.908). The optimum conditions showed that maximum biomass (327 mg/L) at the temperature of 30 °C, pH of 7.5 and 16:8 (Light: Dark cycle), whereas the higher amount of DHA (13.3%) and EPA (9.0%) was observed in the conditions of 18 °C, pH of 7.5 and 16:8 (Light: Dark cycle). The biomass content was directly proportional to the temperature whereas DHA content was inversely proportional. It was revealed that the mRNA expression of EPA and DHA specific desaturases (5Des & 4Des) were significantly elevated in low temperature (20 °C) conditions. The results were highly correlated with the fatty acid profile of Isochrysis sp. grown under low temperature (20 °C) conditions which enhanced the EPA and DHA levels. This study suggests that the temperature is the most influencing factor which can be exploited in the industrial application of DHA and EPA production from Isochrysis sp.

Molecular cloning and functional analysis of a Δ12-fatty acid desaturase from the Antarctic microalga Chlamydomonas sp. ICE-L

Chlamydomonas sp. ICE-L, which can thrive in extreme environments of the Antarctic, could represent a promising alternative for polyunsaturated fatty acid (PUFA) production. A new Δ¹²-fatty acid desaturase (FAD)-encoding gene (Δ ¹² CiFAD), 1269 bp in size, was cloned from Chlamydomonas sp. ICE-L. Bioinformatics analysis showed that Δ ¹² CiFAD-encoded protein was homologous to known FADs with conserved histidine motifs, and localized to the chloroplast. Functional analysis of Δ ¹² CiFAD indicated that recombinant Synechococcus 6803 expressing Δ¹²CiFAD could accumulate C18:2, whereas recombinant Saccharomyces cerevisiae expressing this enzyme could not accumulate C18:2 or any other new fatty acids. These results indicate that Δ¹²CiFAD is a functional enzyme in the chloroplast that can adjust Chlamydomonas sp. ICE-L cell membrane fluidity to adapt to Antarctic extreme low-temperature environments, which give us insights into the frigostable and cold-resistant mechanisms of hypothermic organisms.