# DUR3 as a Molecular Lever for Coordinated Nitrogen and Phosphorus Uptake in Microalgae

## TL;DR

This study shows that overexpressing the DUR3 gene in microalgae improves their ability to absorb nitrogen and phosphorus from wastewater, making them more effective for bioremediation.

## Contribution

The study identifies DUR3 as a key gene that coordinates nitrogen and phosphorus uptake in microalgae, offering a new genetic target for wastewater treatment.

## Key findings

- DUR3 overexpression significantly improves urea uptake and photosynthesis in Chlamydomonas reinhardtii.
- DUR3-OE strains show enhanced nitrogen and phosphorus accumulation under mixed nutrient conditions.
- Transcriptomic analysis reveals DUR3 reprograms a network involving nutrient metabolism and photosynthesis.

## Abstract

This study explored how to improve the ability of microalgae to clean wastewater by efficiently absorbing nitrogen (N) and phosphorus (P), which are essential for plant growth but can also cause water pollution. By focusing on the green alga Chlamydomonas reinhardtii, they discovered that overexpression of a specific gene, DUR3, significantly improves urea uptake. This enhanced absorption leads to better growth and optimizes photosynthesis under various N conditions. Moreover, it increases the alga’s capacity to simultaneously take up both N and P from mixed nutrient sources, although this P enhancement is absent under pure-urea conditions. The research uncovered that DUR3 overexpression triggers a coordinated network of processes within the algae, including nutrient metabolism, photosynthesis, and carbon transport, leading to significant improvements in nutrient uptake efficiency. These findings highlight DUR3 as a key genetic target for developing microalgae strains capable of efficient wastewater bioremediation and contributing to nutrient recycling, offering sustainable strategies for managing water pollution and resource recovery.

Nitrogen (N) and phosphorus (P) are essential macronutrients for plant growth and major pollutants driving aquatic eutrophication. Microalgae represent a sustainable biological platform for nutrient recovery and circular utilization from wastewater; however, the molecular mechanisms governing efficient urea assimilation and its coordination with phosphorus uptake remain inadequately characterized. This study investigated how overexpression of the high-affinity urea transporter gene DUR3 enhances nutrient scavenging capacity in the model green alga Chlamydomonas reinhardtii. The DUR3-overexpressing line exhibited concentration-dependent growth responses to urea, showing significant promotion at low-to-moderate levels but inhibition at high urea concentration or under pure-urea conditions, where DUR3-overexpressing (DUR3-OE) was more severely inhibited than the wild-type (WT). Notably, the DUR3-OE consistently increased chlorophyll content and photosynthetic efficiency (Fv/Fm) under ammonium, urea, and mixed-N regimes. Under low-urea conditions, the total P content of the DUR3-OE was 8.8% higher and total N content was 4.3% higher than in WT (p < 0.05). Except in pure-urea medium, the engineered strains exhibited significantly increased total P accumulation and superior P recovery efficiency from the culture medium. Transcriptomic analysis revealed that DUR3 overexpression reprograms a coordinated regulatory network associated with N/P metabolism, photosynthesis, and carbon transport pathways. RT-qPCR validation confirmed significant upregulation of PMA2 (plasma membrane H+-ATPase), phosphate transporters (PTB3, PTB7), the inorganic carbon transporter HLA3, and photosynthesis-related genes, which was associated with improved nutrient assimilation and photosynthetic performance. These findings establish DUR3 as a key genetic target for engineering microalgae with optimized N-P co-uptake capacity, providing a robust molecular framework for developing high-efficiency algal strains for wastewater bioremediation and nutrient circular economy applications.