Project description:Arthrospira is an edible cyanobacterium used in the food supplement “Spirulina”. The aim of this work was to characterise its response to ionising radiation. Live cells of Arthrospira sp. PCC 8005 were irradiated with 60Co gamma rays. Arthrospira sp. PCC 8005 recovered and resumed photosynthetic proliferation after exposure to a dose of even 6400 Gy, which is a dose about 1000x higher than the lethal dose for most plant, animal and human cells. Biochemical, proteomic and transcriptomic analysis after irradiation with 3200 or 5000 Gy showed a strong reduction in photosynthesis activity and reduced pigment content. Irradiated cells showed reduced transcription for carbon fixation, and for pigment, lipid and secondary metabolite synthesis; while induced transcription of thiol-based antioxidant systems, photosensing and signalling pathways. Cells irradiated with 3200 or 5000 Gy did not show clear dsDNA damage, but transcriptomics did show significant activation of ssDNA repair systems and mobile genetic elements at RNA-level. Irradiated cells also expressed a group of conserved proteins of which the function in radiation resistance remains to be elucidated. This study revealed for the first time the high radiation resistance of Arthrospira, and the molecular systems involved, paving the way for its further exploitation for radiation protection.
Project description:Cyanobacteria have a strong potential for biofuel production due to their ability to accumulate large amounts of carbohydrates. Nitrogen (N) stress can be used to increase the content of carbohydrates in the biomass, but it is expected to reduce biomass productivity. To study this trade-off between carbohydrate accumulation and biomass productivity, we characterized the biomass productivity, biomass composition as well as the transcriptome and proteome of the cyanobacterium Arthrospira sp. PCC 8005 cultured under N-limiting and N-replete conditions. N limitation resulted in a large increase in the carbohydrate content of the biomass (from 14 to 74%) and a decrease in the protein content (from 37 to 10%). Nevertheless, it did not affect the biomass productivity of the culture up to five days after N was depleted from the culture medium. Transcriptomic and proteomic analysis indicated that de novo protein synthesis was down-regulated in the N-limited culture. Proteins were degraded and partly converted into carbohydrates through gluconeogenesis. Cellular N derived from protein degradation was recycled through the TCA and GS-GOGAT cycles. In addition, photosynthetic energy production and carbon fixation were both down-regulated, while glycogen synthesis was up-regulated. Our results suggested that N limitation resulted in a redirection of photosynthetic energy from protein synthesis to glycogen synthesis. The fact that glycogen synthesis has a lower energy demand than protein synthesis might explain why Arthrospira is able to achieve a similar biomass productivity under N-limited as under N-replete conditions despite the fact that photosynthetic energy production was impaired by N limitation.
