Lipid content in transgenic algae line detected through Nile red staining method. After 4 days cultivation in HSM medium, less oil droplets of CrCIS transgenic algae had been found. pCAMBIA-2: pMCAMBIA1302 transgenic algae strain number 2; pCAMCIS-13: pCAMCIS transgenic algae strain number 13.
The biomass and lipid content detected through Nile Red staining method and TAG level of over-expression of CrCIS in transgenic algae in HSM medium. A) The growth curve of CrCIS transgenic algae. B) The lipid content detected through Nile Red staining method of CrCIS transgenic algae. C) TAG level detected through GC/MS after the strains cultivated for 6 days. pCAMBIA-2(8,16): pMCAMBIA1302 transgenic algae strains; pCAMCIS-13(28,54): pCAMCIS transgenic algae strains.
In this study, CrCIS gene silencing increased TAG production by 169.5% in algal cells. CrCIS activity decreased by 16.7% to 37% in transgenic strains compared with that of the control. The mRNA levels of DGAT2 and PAP2 that are directly related to lipid biosynthesis significantly increased. Conversely, overexpression of CrCIS gene decreased the TAG level by 45% but increased CrCIS activity by 209% to 266% in transgenic algae. This result suggested that the silencing or overexpression of CrCIS gene caused photosynthetic carbon flux to enter fatty acid synthesis or the TCA cycle, thereby controling the lipid synthesis in cells.
The biomass and lipid content detected through Nile Red staining method and TAG level in CrCIS RNAi transgenic C. reinhardtii . A) The growth curve of CrCIS RNAi transgenic algae. B) The lipid content detected Nile Red staining method of CrCIS RNAi transgenic algae. C) TAG level detected by GC/MS after the strains cultivated for six days. Maa7-4(10,19): pMaa7IR/XIR transgenic algae strains; CIS-RNAi-1(28,65): pMaa7IR/CrCISIR transgenic algae strains.
Considering that fossil fuel resources are limited, the importance of conserving energy and saving the environment is gaining increased interest. Microalgae biodiesel, a crucial renewable biomass energy that uses solar energy to fix CO2 into biomass, is the most promising alternative to fossil fuels. However, studies on lipid metabolism in eukaryotic, single-celled, photosynthetic microalgae are limited compared with those on oil crops. Basic knowledge on microalgae is less than that of crops, such as rice, wheat, and corn. With the intensification of microalgae-derived biodiesel research at the global scale, more researchers are focusing on the mechanism underlying the formation of high lipid production and high cell-density cultures. These processes are crucial in genetic strain improvement, as well as in the future cultivation of commercial and industrial microalgae.
The synthesis of DHA occurs by the elongation and desaturation of C18 PUFA through EPA and not by retro-conversion of 24:6 n-3.
An update on sustainable sources of n-3 oils may be consulted ().
An extensive review of the membrane properties of DHA may be consulted for further information ().
EPA contained in galactosyl diglycerides and phospholipids of marine diatoms was shown to be the source of a short-chain aldehyde, heptadienal (7:2 n-3), which participates to deleterious effects on zooplankton crustaceans ().
DHA was shown to be oxidized, as arachidonic acid, into isoprostane-like compounds () which seem to be of great value to appreciate oxidative injury to the neural tissues and to generate hydroxylated derivatives () which are potent in preventing inflammation (resolvins, neuroprotectins).
A novel fatty acid derivative named zooxanthellactone was isolated from several strains of symbiotic microalgae, dinoflagellates of the genus Symbiodinium (
The regulation of lipid biosynthesis is essential in photosynthetic eukaryotic cells. This regulation occurs during the direct synthesis of fatty acids and triacylglycerols (TAGs), as well as during other controlling processes in the main carbon metabolic pathway.
In this study, the mRNA levels of Chlamydomonas citrate synthase (CrCIS) were found to decrease under nitrogen-limited conditions, which suggests suppressed gene expression. Gene silencing by RNA interference (RNAi) was conducted to determine whether CrCIS suppression affected the carbon flux in TAG biosynthesis. Results showed that the TAG level increased by 169.5%, whereas the CrCIS activities in the corresponding transgenic algae decreased by 16.7% to 37.7%. Moreover, the decrease in CrCIS expression led to the increased expression of TAG biosynthesis-related genes, such as acyl-CoA:diacylglycerol acyltransferase and phosphatidate phosphatase. Conversely, overexpression of CrCIS gene decreased the TAG level by 45% but increased CrCIS activity by 209% to 266% in transgenic algae.
Cultured under specific and tightly controlled conditions, these algae produced commercially oils which are used in infant formula, foods, beverages, and a variety of supplements ().
More interestingly, an alternative pathway for DHA biosynthesis (the anaerobic polyketide synthase pathway) was also reported recently to occur in microorganisms including bacteria and some eukaryotes including (Heteroconta, Thraustochytriidae) ().
The regulation of CrCIS gene can indirectly control the lipid content of algal cells. Our findings propose that increasing oil by suppressing CrCIS expression in microalgae is feasible.
It is likely that these fatty acids arise from asymbiotic relationship of bacteria with the host cells of marineinvertebrates. Two 5,9 trienoic acids have been identified for the firsttime in triacylglycerols from mollusk gonads, 5,9,15-22:3 and 5,9,15-24:3 ().
While all these unsaturated fatty acids were isolated from phospholipids, apolyethylenic fatty methyl ester (5,9,23-30:3) was isolated from a Mediterraneansponge ( Demospongiae) ().
Based on the distribution of 5,9 fatty acids it may conclude that thebiosynthetic pathways of invertebrates, sponges, myxomycetes, and some plantshave a common enzymatic system to synthesize 5,9 ethylene-interrupted dienoicacids.