Study On The Effect Of Culture Conditions On Porphyridium Purpureum Bioactive Products And Molecular Mechanism

Genus Porphyridium is a primitive single-celled red algae widely distributed in seawater,freshwater,and moist soil.It can synthesize bioactive substances such as phycoerythrin,extracellular polysaccharides and polyunsaturated fatty acids during the growth process.Therefore,the use of different environmental factors to achieve the large-scale accumulation of required bioactive substances has become the key to Porphyridium research.In recent years,research on the culture conditions of Porphyridium has been relatively rare,and previous literatures only focused on the effects of a certain culture condition on one bioactive product.However,the responses to different environmental factors of the most valuable bioactive substances in Porphyridium,including phycoerythrin,polysaccharides and fatty acids,have not been systematically studied,and molecular mechanism underlying such metabolic change remains elusive.In this paper,the culture and bioactive substance yield of Porphyridium purpureum were studied by setting salinity,nitrogen-to-phosphorus ratio,and pH at different gradient levels.The main findings are as follows:The effects of salinity,nitrogen-to-phosphorus ratio,and pH on the algal growth,polysaccharides,phycoerythrin,and total lipid content of P.purpureum were studied.The results showed that the optimal conditions for the growth of P.purpureum were salinity 34 ppt,nitrogen-to-phosphorus ratio 169:1,and pH8;the optimal conditions for obtaining the polysaccharides were salinity 17 ppt,nitrogen-to-phosphorus ratio 14:1,and pH8;the optimal conditions for obtaining phycoerythrin were salinity 17 ppt,nitrogen-to-phosphorus ratio 68:1,and pH 8;the optimal conditions for obtaining the lipids were salinity 34 ppt,nitrogen-to-phosphorus ratio 1:1,and pH8.In actual production applications,culture conditions should be set according to different product accumulation purposes in order to achieve the optimal production efficiency.The most unique biological characteristic of P.purpureum is their special extracellular sulfated polysaccharides,which play a role in protecting it against salt stress.Adaptation to stress is associated with metabolic adjustments.However,molecular mechanism underlying such metabolic change remains elusive.This study presents the first transcriptome profiling of P.purpureum.A total of 8,019 assembled transcripts were identified,annotated and classified into different biological categories and pathways based on BLAST against diverse databases.The in-depth analysis revealed that many of differentially expressed genes in P.purpureum under salinity 68 ppt versus nitrogen salinity 0 ppt involved in the polysaccharides metabolism.Comparison results of gene expression levels under different salinities revealed that polysaccharides synthesis pathway significantly up-regulated under salinity 68 ppt.The increased expression of transcripts corresponding to FBP,pfk A,CS,pgm,USP,UGP2,gal E,and MPI in polysaccharide synthesis pathway and ATP2,ATP6 in energy metabolism when analyzed using real-time PCR revealing the molecular mechanism of high-salt adaption.This sequencing dataset and analysis may serve as a valuable resource to study the mechanisms involved in abiotic stress tolerance in Rhodophyta.