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Synthetic microalgal–bacterial symbiotic system integrating oxidase-protease fusion enzyme for simultaneous removal of recalcitrant nitrogen-containing organic compounds and PET microplastics
Summary
Scientists engineered algae and bacteria to work together as a pollution-cleaning team, using a newly discovered enzyme to break down both toxic nitrogen chemicals and PET microplastics found in industrial wastewater. This matters because current wastewater treatment struggles to remove these stubborn pollutants, meaning they can end up in rivers, drinking water, and eventually our bodies, this new microbial system offers a more effective way to filter them out before they reach the environment.
Industrial wastewaters-particularly those from the printing and dyeing sector-contain complex mixtures of recalcitrant nitrogen-containing organic compounds and microplastics that resist conventional treatment. Here we report a previously undescribed oxidase-protease fusion enzyme (A20674), discovered through transcriptomic analysis of wastewater-acclimated Chlorella vulgaris. Domain dissection reveals that the oxidase-like region drives broad-spectrum removal of N-heterocyclic and aromatic compounds, while the protease-like domain removes organic nitrogen. Engineered overexpression of this enzyme boosted organic nitrogen removal up to fifty-five-fold (final concentration 13-100 mg/L) across different industrial wastewaters. Capitalizing on this metabolic specialization, we constructed a synthetic microalgal-bacterial consortium in which Pseudomonas putida uses microalgal extracellular polysaccharides (EPS) as a carbon source to sustain growth, while supplying indole-3-acetic acid that stimulates microalgal biomass and EPS production. Reciprocal engineering of EPS overproduction in C. vulgaris and enhanced polysaccharide-catabolism in P. putida amplified this mutualistic loop. An evolved, PETase/MHETase-expressing P. putida strain simultaneously acquired elevated IAA output, further strengthening the symbiosis. The optimized consortium reduced organic nitrogen concentrations by sixteen-fold to discharge-compliant levels (≤5 mg/L), enhanced removal of recalcitrant organic nitrogen compounds by five-fold (final concentration 34 mg/L), and improved PET microplastic removal by nine-fold (initial concentration 1 g/L and final concentration 684 mg/L) in printing and dyeing wastewater. These findings uncover a bifunctional enzyme architecture for degrading structurally diverse industrial pollutants, and establish a synthetic-ecology framework for integrated removal of dissolved nitrogen-containing organic compounds and particulate microplastics-a combination unattainable by any single organism or conventional treatment process.