Background Arachidonic acid (ArA) is important for human health because it is one of the major components of mammalian brain membrane phospholipids. The interest in ArA inspired the search for a new sustainable source, and the green microalga Myrmecia incisa Reisigl H4301 has been found a potential ArA-producer due to a high content of intracellular ArA. To gain more molecular information about metabolism pathways, including the biosynthesis of ArA in the non-model microalga, a transcriptomic analysis was performed. Results The 454 pyrosequencing generated 371,740 high-quality reads, which were assembled into 51,908 unique sequences consisting of 22,749 contigs and 29,159 singletons. A total of 11,873 unique sequences were annotated through BLAST analysis, and 3,733 were assigned to Gene Ontology (GO) categories. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis uncovered a C4-like photosynthesis pathway in M . incisa . The biosynthesis pathways of lipid particularly those of ArA and triacylglycerol (TAG) were analyzed in detail, and TAG was proposed to be accumulated in oil bodies in the cytosol with the help of caleosin or oil globule-associated proteins. In addition, the carotenoid biosynthesis pathways are discussed. Conclusion This transcriptomic analysis of M . incisa enabled a global understanding of mechanisms involved in photosynthesis, de novo biosynthesis of ArA, metabolism of carotenoids, and accumulation of TAG in M. incisa . These findings provided a molecular basis for the research and possibly economic exploitation of this ArA-rich microalga.

In order to understand the metabolic pathway of arachidonic acid and other lipids in Myrmecia incisa,the transcriptome pyrosequencing of this microalga was conducted by use of the sequencer Roche 454 GS FLX.Totally 393 722 reads(minimal size〉29 bp) averaging 333 bp were generated from one consecutive pyrosequencing run.Cleaning of the raw sequences resulted in a total of 382 468 high quality reads with an average length of 322 nucleotides totalling 123 Mb.After clustering and assembly,these reads were assembled into 22 714 contigs and 25 621 singletons.The average length for contigs and singletons were 639 bp and 277 bp,respectively.By annotating the unisequences,the metabolic pathways of lipids were constructed.Fatty acid was de novo synthesized in chloroplasts,and free fatty acids were transported into cytosol where triacylglycerol was synthesized by endoplasmic reticulum.Oil bodies were formed possibly with the help of caleosins.Arachidonic acid was synthesized by desaturation for several times and elongation from oleic acid.Oleic acid was formed by stearoyl-ACP desaturase,whereas palmitoic acid bound with glucolipid was generated by Δ7 desaturase.This research lays a foundation for systematic investigation into the manipulation of lipid metabolism and gene modification for higher production of ArA in M.incisa.

The way of " extracting-sahing-chromatography" was used to purify the phycoerythrin and phyeoeyanin from Porphyra yezoensis in process scale-up. First, by comprehensive comparison of efficiency, the Sephadex G-25 was selected from four resins (Sephadex G-25 、G-100、S-300 and CL-6B) as the best choice used in crude extract desalting of phycobiliprotein. Then the preparation process of phycobiliprotein was scaled-up with raw material(Porphyra yezoensis) increased from 1 g to 20g, and finally to 400g. The results indicated that the yields of purified phyeoerythrin and phycocyanin (absorption spectra purity above 3. 2) increased during according to process scale-up,with 0.323% phycoerythrin and 0. 148% phycocyanin obtained from 400g frozen Porphyra yezoensis blades respectively. It is no doubt that the process involved in the experiment is a potential way for large scale preparation of phyeobiliproteins of high purity.