氮、磷限制下原绿球藻的生理响应及分子机制OA

[Objective]Prochlorococcus is the smallest and most abundant photoautotrophic organism in the oligotrophic ocean,playing a crucial role in global primary production and biogeochemical cycling.Among the environmental factors affecting its growth,nitrogen(N)and phosphorus(P)nutrients are recognized as the most critical,as they serve as essential elements for the synthesis of key cellular components.This study aims to investigate the effects of N and P limitation on the physiological traits of Prochlorococcus,as well as to elucidate its molecular response mechanisms,with a particular focus on how N and P scarcity influences key physiological parameters,including growth,carbon fixation capacity,pigment content,and global gene expression patterns.[Methods]In this study,the HL Ⅱ P.marinus AS9601 strain was selected as the experimental model.A nutrient-limited culture system was established,including a N-limited condition[c(NH4+)∶c(PO43-)=1.6],a P-limited condition[c(NH4+)∶c(PO43-)=160],and a control group with balanced nutrient availability[c(NH4+)∶c(PO43-)=16].Multiple physiological parameters were systematically measured,including growth rate,cell volume,pigment content,particulate organic carbon(POC)accumulation,and dissolved organic carbon(DOC)release.In addition,transcriptomic analysis was performed under N-limited conditions to investigate genome-wide changes in gene expression.This analysis identified genes that were significantly up-or down-regulated,providing insights into the molecular responses of P.marinus AS9601 to N limitation.[Results]Under N limitation,the availability of inorganic N decreased significantly,resulting in a pronounced inhibition of organic compound synthesis that depends on inorganic N as a substrate.Among these,the synthesis of light-harvesting pigments,which require substantial N investment,decreased by approximately 62％.This reduction in pigment content led to a substantial impairment of photosynthetic carbon fixation,with CO2 fixation rate declining by 65％.Consequently,intracellular organic carbon accumulation decreased by approximately 41％,biomass growth was limited,and the cells exhibited 72％reduction in maximum specific growth rate and 10％decrease in cell volume.Compared with N limitation,P.marinus AS9601 displayed similar physiological changes under P limitation,although the magnitude of these changes was smaller,with P deficiency causing 27％reduction in maximum specific growth rate and 8％decrease in cell volume.Transcriptomic analysis further revealed that under N limitation,P.marinus AS9601 preferentially allocated limited cellular resources to the synthesis of genetic material while downregulating the expression of genes associated with the photosynthetic apparatus and ribosomal machinery,suggesting an adaptive strategy to reallocate cellular resources under nutrient stress.[Conclusion]In summary,both N and P limitation resulted in the weakening of multiple physiological phenotypes in P.marinus AS9601,including decreased growth rate,reduced cell volume,diminished pigment content,and impaired carbon fixation capacity.N limitation exhibited more pronounced effects,accompanied by adjustments in resource allocation at the transcriptomic level.These findings comprehensively reflect the physiological and molecular response characteristics of Prochlorococcus under nutrient-limited conditions and provide valuable insights into its adaptive strategies for coping with nutrient scarcity in oligotrophic marine environments.