Tokyo Tech team engineers Nannochloropsis algae to boost oil production; method potentially applicable to other strains
08 September 2015
Researchers at the Tokyo Institute of Technology and colleagues have engineered the Nannochloropsis algal strain NIES-2145 to enhance the production of fat-based molecules called triacylglycerols (TAGs), thereby increasing oil synthesis from the microalgae. The study’s results suggest that the specific gene promoter used in this work could also be applied across various algae to boost oil production. The paper is published in the journal Frontiers in Microbiology.
Triacylglycerols, or TAGs, are a class of lipids which comprise glycerol attached to three fatty acid chains; microalgae is known to produce more TAGs under nutrient stress conditions. When the algal strain Chlamydomonas reinhardtii is starved of phosphorus, TAGs accumulate rapidly following the overexpression of an enzyme known as CrDGTT4, which in turn is triggered by gene promoter SQD2.
Hiroyuki Ohta at Tokyo Institute of Technology and his team conducted genetic analysis of NIES-2145 and uncovered a homolog of the SQD2 gene. This implied a common expression control system between algal species in response to nutrient stress. The researchers decided to place both CrDGTT4 from C. reinhardtii and its SQD2 promoter into NIES-2145 to find out if this combination could control levels of TAGs production.
Their attempt was successful—the SQD2 promoter was able to drive CrDGTT4 expression in NIES-2145 under phosphorus starvation, crucially without disturbing the membrane structure of the microalgae, and the production of TAGs in NIES-2145 increased as a result. Notably, incorporation of oleic acid (a preferentially utilized substrate by CrDGTT4) into TAG molecules was enhanced.
|
|
| Quantitative analysis of various lipids. Cells were cultured in control (+P) or -P medium for 4 days. Each lipid is expressed in nmol per 106 cells of pCrSQD2-CrDGTT4 (#9) and the vector control (VC) lines. Values are the mean ± SD from three independent experiments. Asterisks indicate a statistically significant difference compared with VC based on a two-tailed Student’s t-test (*P < 0.05). MGDG, DGDG and SQDG are chloroplast membrane glycolipids. PG, PE, PC, PS and PI are membrane phospholipids. DGTS is a betaine lipid. Source: Hiroyuki Ohta. Click to enlarge. |
The findings point to the possibility of manipulating the production of TAGs, and therefore biofuel oil production, in multiple microalgal strains.
The ability to harness the estimated 40-50 thousand liters of oil per hectare per year generated by algae is a prime motivation behind Ohta’s team’s research. Following extensive studies into the model organism for studying algal biofuel production, C. reinhardtii, the team began to find genetic correlations between it and other algal strains.
A key finding of this research is that the SQD2 gene appears common to many types of algae, including primary and secondary endosymbiotic algae. The results of this study indicate that the SQD2 promoter from one type of algae can be used to trigger overexpression of the enzyme CrDGTT4, and thus increase yields of TAGs, in another algal strain. This suggests that genetic manipulation using the SQD2 promoter could increase oil yields from various algae.
Further investigations are needed in order to fully understand the processes behind lipid remodeling during phosphorus starvation in algae before these methods are tested on a larger scale.
Resources
Masako Iwai, Koichi Hori, Yuko Sasaki-Sekimoto, Mie Shimojima and Hiroyuki Ohta (2015) “Manipulation of oil synthesis in Nannochloropsis strain NIES-2145 with a phosphorus starvation-inducible promoter from Chlamydomonas reinhardtii” Frontiers in Microbiology 159028 doi: 10.3389/fmicb.2015.00912
This is very interesting. Starvation of sulfur plus darkness in some algae promotes hydrogen generation. Starvation of phosphorus promotes production of triacylglycerols. Perhaps gene-modified algae could do this with easier and cheaper prompts.
Posted by: Engineer-Poet | 09 September 2015 at 10:23 PM