Overexpression of flv3 improves photosynthesis in the cyanobacterium Synechocystis sp. PCC6803 by enhancement of alternative electron flow

Abstract

BackgroundTo ensure reliable sources of energy and raw materials, the utilization of sustainable biomass has considerable advantages over petroleum-based energy sources. Photosynthetic algae have attracted attention as a third-generation feedstock for biofuel production, because algae cultivation does not directly compete with agricultural resources, including the requirement for productive land and fresh water. In particular, cyanobacteria are a promising biomass feedstock because of their high photosynthetic capability.ResultsIn the present study, the expression of the flv3 gene, which encodes a flavodiiron protein involved in alternative electron flow (AEF) associated with NADPH-coupled O2 photoreduction in photosystem I, was enhanced in Synechocystis sp. PCC6803. Overexpression of flv3 improved cell growth with corresponding increases in O2 evolution, intracellular ATP level, and turnover of the Calvin cycle. The combination of in vivo13C-labeling of metabolites and metabolomic analysis confirmed that the photosynthetic carbon flow was enhanced in the flv3-overexpressing strain.ConclusionsOverexpression of flv3 improved cell growth and glycogen production in the recombinant Synechocystis sp. PCC6803. Direct measurement of metabolic turnover provided conclusive evidence that CO2 incorporation is enhanced by the flv3 overexpression. Increase in O2 evolution and ATP accumulation indicates enhancement of the AEF. Overexpression of flv3 improves photosynthesis in the Synechocystis sp. PCC6803 by enhancement of the AEF.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0183-x) contains supplementary material, which is available to authorized users.

Dynamic metabolic profiling together with transcription analysis reveals salinity-induced starch-to-lipid biosynthesis in alga Chlamydomonas sp. JSC4

“…The levels of metals in the medium are described in the previous report43. After 3 days’ pre-culture, cells were inoculated into double-deck photobioreactor44, which has a first stage containing 2M NaHCO 3 /Na 2 CO 3 to supply the desired concentration of CO 2 , and a second stage containing the culture broth, at an initial cell concentration of 20 mg L −1 . The cells were cultured under the conditions as follows; light intensity, 250 μmol photons m −2 s −1 (white fluorescent lamps); CO 2 aeration, 2% CO 2 ; temperature, 30 °C.…”

Evaluation of New Genetic Toolkits and Their Role for Ethanol Production in Cyanobacteria

“…Improving the availability of the precursor pyruvate could be another starting point to increase the ethanol yield, which, for example, could be achieved by the increase of CO 2 fixation or the knock-out of competitive metabolic pathways like the glycogen synthesis pathway [12,72]. The increase of the photochemical efficiency by overexpression of genes participating in photosynthesis like the flv3 gene, which encodes a flavodiiron protein shown by Hasunuma et al [81], could be used for improving the productivity, too. Here, the overexpression of flv3 lead to an increased availability of metabolites of the Calvin cycle and thus enhanced the growth rate and CO 2 fixation [81].…”

Cyanobacterial photo-driven mixotrophic metabolism and its advantages for biosynthesis

“…To reduce photooxidative stresses, cyanobacteria employ an alternative electron flow pathway (i.e., water-water cycle) that uses electrons extracted from water by PSII to re-generate H 2 O in PSI. This reaction dissipates excess excitation energy and reduces NADPH yields, but moderately enhances photosynthetic ATP generation and oxygen evolution [9]. Due to photoinhibition, the surface illumination condition has to be confined to avoid damaging the light-sensitive PSII centers in photobioreactors.…”

“…Because of this, researchers are interested in pigments that may absorb light at broader wavelengths. Some cyanobacteria's PBSs contain special phycobiliproteins that absorb colorful light [8,9]. PBSs: light harvesting antenna phycobilisomes; Cyt b 6 f: cytochrome b 6 f complex; PSI: photosystem I; PSII: photosystem II then pass energy on to chlorophylls during photosynthesis [15].…”