Transcriptome Analysis and Physiological Responses of Economic Macroalga Gracilariopsis lemaneiformis under Sulfate Deficiency

Sulfur is an essential macronutrient for the growth of all photosynthetic organisms and plays important roles in different metabolic pathways.However,sulfur metabolism and its related research on macroalgae with important ecological value is rather limited.In this study,marine ecological valued macroalga Gracilariopsis lemaneiformis was used to study the general physiological responses and transcriptome profiling under the sulfate deficiency.The relative growth rate of algae under sulfate deficiency was statistically significantly lower than that of control after 6 days.However,no significant differences were observed in the pigments content and Fv/Fm value,indicating that the photosynthesis was not obviously affected under the sulfate deficiency.Furthermore,the significantly increased soluble protein and carbohydrate contents,and indistinctively differentially expressed sulfate transporter/permease(ST)and ATP sulfurylase(ATPS)genes suggesting that G.lemaneiformis cells did not use sulfur from internal protein and carbohydrate pools but utilize stored sulfur from vacuole to satisfy their nutritional requirements during the sulfate deficiency.Transcriptome data showed that most annotated differentially expressed genes(DEGs)were down-regulated under the sulfate deficiency,including a large proportion of genes involved in the pathway of sulfur metabolism.Therefore,it was concluded that the pathway of sulfur metabolism was suppressed under the sulfate deficiency in G.lemaneiformis.The results and analysis in this study provide a comprehensive understanding for the physiological and molecular response of G.lemaneiformis to sulfate deficiency.

Effects of Various Light-Emitting Diode(LED)Wavelengths on the Growth of Scenedesmus Obliquus Fachb-12 and Accumulation of Astaxanthin

Given the central role of light in the algal photosynthesis,respiration,cell division,growth and the accumulation of value products,the effects of light-emitting diodes(LEDs)light wavelengths(blue,white,red and green)were studied in Scenedesmus obliquus.Biomass,residual nutrient amount,soluble protein,astaxanthin and reactive oxygen species,superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD)activity were analyzed to determine the effects of different monochromatic light wavelengths via biochemical methods.The results showed that blue light wavelength is the optimal light wavelength for phosphorus removal efficiency and the accumulation of biomass and astaxanthin in S.obliquus.Meanwhile,high reactive oxygen species content under the blue light might induce the accumulation of astaxanthin.The high activity of SOD,CAT and POD might participate in clearing the reactive oxygen species to facilitate the growth of microalgae.Furthermore,we found mixed blue/green lights treatment is the most appropriate mixture for the nitrogen removal.Under the blue light treatment,high light intensity and 18L:6D light cycle is the best condition for biomass and astaxanthin accumulation.Optimal nitrogen/phosphorus removal efficiency was observed under a 24L:0D light cycle.These results might provide a foundational data for the optimizing the productivity of high-value metabolites and treatment of wastewater.