Efficient degradation of sulfadiazine by photosynthetic cyanobacteria Synechocystis sp. PCC 6803 coupling with recombinant laccase strategy

As an emerging technology, photosynthetic algae have great potential for bioremediation of various organic pollutants in wastewater. However, the application of recombinant enzyme strategy in algae bioremediation is still in its infancy. In this study, the removal effect of sulfadiazine (SDZ) by Synechocystis sp. PCC 6803 was thoroughly explored. The removal rate of 0.5–2 mg/L SDZ reached more than 85% within 60 h, which is the highest level reported in algae. Biodegradation was the primary mechanism, with ∼ 24.5% SDZ removed by combining photolysis and hydrolysis. In-depth analysis of the transformation pathway confirmed that laccase was the main enzymatic contributor to biodegradation. The medium syringic acid was added to form a laccase-mediator system, and the removal rate was increased by 101%. Furthermore, the recombinant laccase strategy was innovatively adopted to introduce efficiency heterogeneous laccase. A combination test was conducted on three modules (neutral site, promoter, and chaperone protein), and the optimal transformant increased the removal rate by 62%. In a word, this work elucidates the biodegradation pathway of SDZ by Synechocystis sp. in detail, reveals the critical role of laccase in algae bioremediation, which hope to accelerate the green and sustainable bioremediation process of antibiotics even a series of organic pollutants.