Transcriptomic Insights into Metabolic Reprogramming and Exopolysaccharide Synthesis in Porphyridium purpureum Under...

Area of Science:

• Marine biotechnology
• Microalgal physiology
• Biochemical engineering

Background:

• Red microalgae, such as *Porphyridium* species, are recognized for producing bioactive sulfated exopolysaccharides (EPS) with significant industrial and biomedical applications.
• While abiotic stresses like nitrogen deprivation influence EPS production, the precise molecular mechanisms and the role of carbohydrate-activated enzymes (CAZymes) in EPS biosynthesis remain largely unelucidated.
• Understanding these mechanisms is crucial for optimizing EPS production in microalgae.

Purpose of the Study:

• To investigate the physiological, biochemical, and transcriptomic responses of *Porphyridium purpureum* to progressive nitrogen deprivation.
• To elucidate the metabolic regulation and identify key carbohydrate-activated enzymes (CAZymes) involved in exopolysaccharide (EPS) biosynthesis under nitrogen-limited conditions.
• To establish a link between nitrogen availability, carbon metabolism, and EPS production.

Main Methods:

• Integrated physiological, biochemical, and transcriptomic analyses (RNA-Seq) of *P. purpureum* under progressive nitrate consumption.
• Quantitative real-time PCR (RT-qPCR) was employed for transcriptomic data validation.
• Analysis focused on metabolic shifts, EPS release, and the expression of CAZyme families.

Main Results:

• *P. purpureum* exhibited a phase-dependent metabolic adaptation to nitrogen stress, with EPS release correlating to reduced nitrate uptake.
• Transcriptomic analysis revealed a global metabolic downregulation coupled with the upregulation of stress-responsive pathways, carbohydrate catabolism, and nucleotide-sugar synthesis.
• Specific upregulation of CAZyme families GT4, GT8, and GT77 was observed, indicating their potential role in EPS biosynthesis.

Conclusions:

• Nitrogen and carbon metabolic pathways are coordinately regulated to govern polysaccharide biosynthesis in *P. purpureum* under nitrogen stress.
• The study provides insights into the molecular mechanisms driving EPS production in response to nutrient limitation.
• Findings open avenues for future research into enzyme compartmentalization and flux distribution in nitrogen-stressed microalgae.