Wastewater nutrients valorization into biostimulant via engineered polyphosphate-accumulating bacterium

Area of Science:

• Environmental Microbiology
• Biotechnology
• Circular Economy

Background:

• Phosphorus (P) and nitrogen (N) are essential nutrients often lost in wastewater.
• Current wastewater treatment methods prioritize removal over nutrient recycling and valorization.
• There is a need for innovative solutions to recover and reuse these valuable resources.

Purpose of the Study:

• To engineer a microbial strain for simultaneous valorization of P and N from municipal wastewater.
• To optimize conditions for enhanced intracellular accumulation of polyphosphate (polyP) and spermidine (Spd).
• To evaluate the potential of the recovered nutrients as a biostimulant for plant growth.

Main Methods:

• Engineering Citrobacter freundii (CPP) to overexpress ppk for enhanced P uptake.
• Optimizing fermentation conditions for co-accumulation of polyP and Spd.
• Characterizing the composition and properties of intracellular stabilisomes.
• Assessing the efficacy of the CPP-derived biostimulant (CPPB) in plant growth trials.

Main Results:

• Optimized CPP achieved significant intracellular accumulation of polyP (247.56 mg/g) and Spd (102.71 mg/g).
• High P (76.76%) and N (51.16%) valorization rates were achieved, exceeding conventional methods.
• Co-accumulated polyP and Spd formed insoluble stabilisomes, facilitating continuous production.
• CPPB application significantly increased Brassica chinensis dry weight (121.14%) and plant height (31.08%).

Conclusions:

• A practical biorefinery route for simultaneous P and N valorization from wastewater was established.
• The engineered CPP strain offers a sustainable method for nutrient recovery and reuse.
• The CPPB biostimulant demonstrates superior performance compared to commercial fertilizers, advancing the circular bioeconomy.