Enhancement of photosynthetic capacity in Euglena gracilis by expression of cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase leads to increases in biomass and wax ester production

Abstract

BackgroundMicroalgae have recently been attracting attention as a potential platform for the production of biofuels. Euglena gracilis, a unicellular phytoflagellate, has been proposed as an attractive feedstock to produce biodiesel because it can produce large amounts of wax esters, consisting of medium-chain fatty acids and alcohols with 14:0 carbon chains. E. gracilis cells highly accumulate a storage polysaccharide, a β-1,3-glucan known as paramylon, under aerobic conditions. When grown aerobically and then transferred into anaerobic conditions, E. gracilis cells degrade paramylon to actively synthesize and accumulate wax esters. Thus, the enhanced accumulation of paramylon through the genetic engineering of photosynthesis should increase the capacity for wax ester production.ResultsWe herein generated transgenic Euglena (EpFS) cells expressing the cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase (FBP/SBPase), which is involved in the Calvin cycle, to enhance its photosynthetic activity. FBP/SBPase was successfully expressed within Euglena chloroplasts. The cell volume of the EpFS4 cell line was significantly larger than that of wild-type cells under normal growth conditions. The photosynthetic activity of EpFS4 cells was significantly higher than that of wild type under high light and high CO2, resulting in enhanced biomass production, and the accumulation of paramylon was increased in transgenic cell lines than in wild-type cells. Furthermore, when EpFS cell lines grown under high light and high CO2 were placed on anaerobiosis, the productivity of wax esters was approximately 13- to 100-fold higher in EpFS cell lines than in wild-type cells.ConclusionOur results obtained here indicate that the efficiency of biomass production in E. gracilis can be improved by genetically modulating photosynthetic capacity, resulting in the enhanced production of wax esters. This is the first step toward the utilization of E. gracilis as a sustainable source for biofuel production under photoautotrophic cultivation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0264-5) contains supplementary material, which is available to authorized users.

Large-Scale Cultivation of Euglena

“…Recombinant DNA technology has recently succeeded in producing transgenic E. gracilis strains with enhanced photosynthetic potential (Ogawa et al 2015). The successful production of a population of random mutants by heavy-ion beam irradiation and the use of recombinant DNA technology to produce transgenic Euglena coupled with appropriate screening techniques will enable the breeding of E. gracilis with desirable traits suitable for specific commercial applications.…”

“…The development of the methods for the stable and efficient transformation of Euglena (Ogawa et al 2015), will enable the production of diverse GM Euglena. Some possible uses of the GM Euglena include the production of useful recombinant proteins that are difficult to express in other host organisms.…”

Wax Ester Fermentation and Its Application for Biofuel Production

“…Indeed, transgenic tobacco and lettuce plants overexpressing the cyanobacterial FBPase/ SBPase gene, which encodes a bifunctional enzyme having both FBPase and SBPase activities, in chloroplasts showed an enhanced CO 2 assimilation rate and increased biomass production (Miyagawa et al 2001;Yabuta et al 2008). In order to enhance photosynthesis and biomass production in E. gracilis, Ogawa et al (2015) have introduced the cyanobacterial FBPase/SBPase gene into Euglena cells to generate transformed cell lines, EpFS4 and EpFS11. The EpFS4 cells had a larger cell volume and enhanced photosynthetic activity compared to wild-type cells (Fig.…”

Effects of overexpressing photosynthetic carbon flux control enzymes in the cyanobacterium Synechocystis PCC 6803

“…In cyanobacteria, the metabolic function of SBPase is carried out by a bi-functional fructose-1,6-/seduheptoluse-1,7-biphosphatase (FBP/SBPase) which belongs to the FBPase family (Tamoi et al, 1999). Overexpressing plant SBPase, or cyanobacterial FBP/SBPase in plants, resulted in increased growth and photosynthesis even though special growth conditions sometimes were required (Lefebvre et al, 2005;Miyagawa et al, 2001;Ogawa et al, 2015;Rosenthal et al, 2011). Experimental results in plants indicated that the chloroplastic FBPase was also a rate limit enzyme in the CBB cycle with additional influence by SBPase (Ma et al, 2005;Tamoi et al, 2006).…”