Through biotechnology, the team developed a phosphorus hyperaccumulator algal strain, which can efficiently recycle phosphorus in water and realize the vision of phosphorus closed loop. In addition, it provides technical support for the ultimate realization of a virtuous circle of phosphorus and the promotion of green agricultural development.

The relevant research was published in Plant Biotechnology Journal with the title "Engineering microalgae for water phosphorus recovery to close the phosphorus cycle".

Microalgae have the characteristics of high photosynthetic efficiency and good carbon fixation performance. It can luxuriously absorb phosphorus in water and store it in the vacuole in the form of polyphosphate. Phosphorus is an essential element for crop growth. In order to ensure crop yield, a large amount of phosphate rock is mined and made into phosphorus fertilizer and applied to the soil. On the one hand, as a non-renewable resource, phosphate rock is facing the risk of depletion; on the other hand, about 30-50% of the world's phosphate fertilizer is lost into water bodies through soil runoff every year. This causes   environmental problems such as eutrophication of water bodies. For phosphorus in water, the current common treatment method is to absorb and precipitate or form sludge after being absorbed by bacteria and discharged. Although these methods can purify water bodies, they cannot realize the recycling of phosphorus.

In this study, based on the previous analysis of the phosphorus signaling network pathway in microalgae, three methods of microalgae engineering transformation were established through biotechnology methods.

1. Turn off the microalgae vacuolar phosphorus efflux gene, and lock phosphorus in the vacuole;

2. Overexpress the phosphorus core transcriptional regulator PSR1 to improve the luxury absorption capacity of algae strains for phosphorus;

3. Integrate phosphorus signaling and internal transport, that is, overexpress PSR and turn off PTC1 at the same time, develop high-efficiency phosphorus absorption in water and super-accumulating phosphorus algae (SPAO), and increase its total phosphorus content to about 7% of dry weight (highest among plants to date), and vacuole polyphosphate content increased 5 times.

Moreover, SPAO showed obvious phosphorus removal advantages in synthetic wastewater and real industrial wastewater tests. When the algae were inoculated at 106 cells/ml in industrial wastewater with a phosphorus content of about 60 mg/L, the wild-type algal strains could only remove about 50% of the phosphorus, while the SPAO strains only took about 60 hours to remove all phosphorus.

The research team cooperated with Hangzhou Xiuchuan Technology Co., Ltd. to further explore the industrial application of SPAO strains. The team found that SPAO strains have shown good potential in the production of biological phosphate fertilizers, phosphorus recovery, and deep phosphorus removal from wastewater. It is possible to play an important role in the phosphorus cycle of urban ecosystems in the future as well. The excellent algae strain recycles phosphorus and makes microalgae fertilizer, which can not only achieve carbon sequestration, emission reduction, soil improvement, etc., but also meet the requirements of food security and the national "double carbon" strategy.

Figure 1. The design of SPAO and the schematic diagram of promoting phosphorus closed loop

Postdoctoral Wang Long of the IARRP is the first author of the paper, researcher Yi Keke is the corresponding author, and postdoctoral Jia Xianqing is the co-first author and co-corresponding author of the paper. This research was funded by the National Natural Science Foundation of China, the China Postdoctoral Science Foundation and the Innovation Project of the Chinese Academy of Agricultural Sciences.

Paper link: https://onlinelibrary.wiley.com/doi/epdf/10.1111/pbi.14040 

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