Polyunsaturated fatty acids (PUFAs) play an important role in human diet. Despite the wide-ranging importance and benefits from heart health to brain functions, humans and mammals cannot synthesize PUFAs de novo. The primary sources of PUFA are fish and plants. Due to the increasing concerns associated with food security as well as issues of environmental contaminants in fish oil, there has been considerable interest in the production of polyunsaturated fatty acids from alternative resources which are more sustainable, safer, and economical. For instance, marine bacteria, particularly the genus of Shewanella, Photobacterium, Colwellia, Moritella, Psychromonas, Vibrio, and Alteromonas, are found to be one among the major microbial producers of polyunsaturated fatty acids. Recent developments in the area with a focus on the production of polyunsaturated fatty acids from marine bacteria as well as the metabolic engineering strategies for the improvement of PUFA production are discussed.
While the capacity for long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis has been elucidated in vertebrates and several invertebrate phyla, the comparative knowledge in crustaceans remains vague. A key obstacle in mapping the full spectrum of LC-PUFA biosynthesis in crustacean is the limited evidence of the functional activities of enzymes involved in desaturation or elongation of polyunsaturated fatty acid substrates. In this present study, we report on the cloning and functional characterization of two Elovl elongases from the orange mud crab, Scylla olivacea. Sequence and phylogenetic analysis suggest these two Elovl as putative Elovl4 and Elovl6, respectively. Using the recombinant expression system in Saccharomyces cerevisiae, we demonstrate the elongation capacity for C18-C22 PUFA substrates in the S. olivacea Elovl4. The S. olivacea Elovl6 elongated saturated fatty acids, monounsaturated fatty acids, and interestingly, C18-C20 PUFA. Taken together, both Elovl fulfill the elongation steps required for conversion of C18 PUFA to their respective LC-PUFA products. Elovl4 is expressed mainly in the hepatopancreas and gill tissues, while Elovl6 is predominant in digestive tissues. The mRNA expression of both enzymes was higher in mud crabs fed with vegetable oil-based diets. Tissue fatty acid composition also showed the existence of LC-PUFA biosynthesis intermediate products in tissues expressing these two elongases. In summary, we report here two novel Elovl with PUFA elongating activities in a marine brachyuran. This will contribute significantly to the understanding of the LC-PUFA biosynthesis pathway in crustaceans and advance the development of aquafeed for intensive farming of the mud crab.
High cell density cultivation of microalgae via heterotrophic growth mechanism could effectively address the issues of low productivity and operational constraints presently affecting the solar driven biodiesel production. This paper reviews the progress made so far in the development of commercial-scale heterotrophic microalgae cultivation processes. The review also discusses on patentable concepts and innovations disclosed in the past four years with regards to new approaches to microalgal cultivation technique, improvisation on the process flow designs to economically produced biodiesel and genetic manipulation to confer desirable traits leading to much valued high lipid-bearing microalgae strains.
The genus Aureispira consisting of two species, Aureispira marina and Aureispira maritima is an arachidonic acid-producing bacterium and produces secondary metabolites. In this study, we isolated a new Aureispira strain, Aureispira sp. CCB-QB1 from coastal area of Penang, Malaysia and the genome sequence of this strain was determined. The draft genome of this strain is composed of 185 contigs for 7,370,077 bases with 35.6% G+C content and contains 5911 protein-coding genes and 76 RNA genes. Linoleoyl-CoA desaturase, the key gene in arachidonic acid biosynthesis, is present in the genome. It was found that this strain uses mevalonate pathway for the synthesis of geranylgeranyl diphosphate (GGPP), which is precursor of diterpenoid, and novel pathway via futalosine for the synthesis of menaquinones. This is the first draft genome sequence of a member of the genus Aureispira.
The present study aimed to investigate the potential role of dietary petroselinic acid (PSA) in enhancing the n-3 long-chain polyunsaturated fatty acid (LC-PUFA) content in fish tissues. Three isolipidic casein-based diets were formulated to comprise graded levels of PSA (0, 10, or 20% of total fatty acid) with the incremented inclusion of coriander seed oil. Fish growth and nutrient digestibility were not significantly (P > 0.05) influenced by dietary PSA level. In general, dietary PSA affected the fatty acid composition of tilapia tissues and whole-body, which reflected dietary fatty acid ratios. Dietary PSA significantly (P < 0.05) increased β-oxidation, particularly on α-linolenic acid (18:3n-3) and linoleic acid (18:2n-6). This study provided evidence that PSA, a pseudoproduct mimicking the structure of 18:3n-6, did reduce Δ-6 desaturation on 18:2n-6 but, contrary to popular speculation, did not stimulate more Δ-6 desaturase activity on 18:3n-3. The overall Δ-6 desaturase enzyme activity may be suppressed at high dietary levels of PSA. Nevertheless, the n-3 and n-6 LC-PUFA biosynthesis was not significantly inhibited by dietary PSA, indicating that the bioconversion efficiency is not modulated only by Δ-6 desaturase. The deposition of n-3 LC-PUFA in liver and fillet lipids was higher in fish fed PSA-supplemented diets.
The biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFA), a process to convert C18 polyunsaturated fatty acids into eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) or arachidonic acid (ARA), requires the concerted activities of two enzymes, the fatty acyl desaturase (Fads) and elongase (Elovl). This study highlights the cloning, functional characterisation and tissue expression pattern of a Fads and an Elovl from the Boddart's goggle-eyed goby (Boleophthalmus boddarti), a mudskipper species widely distributed in the Indo-Pacific region. Phylogenetic analysis revealed that the cloned fads and elovl are clustered with other teleost orthologs, respectively. The investigation of the genome of several mudskipper species, namely Boleophthalmus pectinirostris, Periophthalmus schlosseri and Periophthalmus magnuspinnatus, revealed a single Fads2 and two elongases, Elovl5 and Elovl4 for each respective species. A heterologous yeast assay indicated that the B. boddarti Fads2 possessed low desaturation activity on C18 PUFA and no desaturation on C20 and C22 PUFA substrates. In comparison, the Elovl5 showed a wide range of substrate specificity, with a capacity to elongate C18, C20 and C22 PUFA substrates. An amino acid residue that affects the capacity to elongate C22:5n-3 was identified in the B. boddarti Elovl5. Both genes are highly expressed in brain tissue. Among all tissues, DHA is highly concentrated in neuron-rich tissues, whereas EPA is highly deposited in gills. Taken together, the results showed that due to the inability to perform desaturation steps, B. boddarti is unable to biosynthesise LC-PUFA, relying on dietary intake to acquire these nutrients.
Lates calcarifer, commonly known as the Asian sea bass or barramundi, is an interesting species that has great aquaculture potential in Asia including Malaysia and also Australia. We have investigated essential fatty acid metabolism in this species, focusing on the endogenous highly unsaturated fatty acid (HUFA) synthesis pathway using both biochemical and molecular biological approaches. Fatty acyl desaturase (Fad) and elongase (Elovl) cDNAs were cloned and functional characterization identified them as ∆6 Fad and Elovl5 elongase enzymes, respectively. The ∆6 Fad was equally active toward 18:3n-3 and 18:2n-6, and Elovl5 exhibited elongation activity for C18-20 and C20-22 elongation and a trace of C22-24 activity. The tissue profile of gene expression for ∆6 fad and elovl5 genes, showed brain to have the highest expression of both genes compared to all other tissues. The results of tissue fatty acid analysis showed that the brain contained more docosahexaenoic acid (DHA, 22:6n-3) than flesh, liver and intestine. The HUFA synthesis activity in isolated hepatocytes and enterocytes using [1-(14)C]18:3n-3 as substrate was very low with the only desaturated product detected being 18:4n-3. These findings indicate that L. calcarifer display an essential fatty acid pattern similar to other marine fish in that they appear unable to synthesize HUFA from C18 substrates. High expression of ∆6 fad and elovl5 genes in brain may indicate a role for these enzymes in maintaining high DHA levels in neural tissues through conversion of 20:5n-3.
The front-end desaturases (Fads) are rate-limiting enzymes responsible for production of long-chain polyunsaturated fatty acids (LC-PUFA). The full spectrum of the transcriptional regulation of fads is still incomplete, as cloning of fads promoter is limited to a few species. Here, we described the cloning and characterisation of the zebrafish fads2 promoter. Using 5'-deletion and mutation analysis on this promoter, we identified a specific region containing the sterol regulatory element (SRE) which is responsible for the activation of the fads2 promoter. In tandem, two conserved CCAAT boxes were also present adjacent to the SRE and mutation of either of these binding sites attenuates the transcriptional activation of the fads2 promoter. An in vivo analysis employing GFP reporter gene in transiently transfected zebrafish embryos showed that this 1754 bp upstream region of the fads2 gene specifically directs GFP expression in the yolk syncytial layer (YSL) region. This indicates a role for LC-PUFA in the transport of yolk lipids through this tissue layer. In conclusion, besides identifying novel core elements for transcriptional activation in zebrafish fads2 promoter, we also reveal a potential role for fads2 or LC-PUFA in YSL during development.