Enhanced Biodegradation of the Organophosphate Pesticide Diazinon Using <i>phoU</i> Knockout Mutant of <i>Synechocystis</i> sp. PCC 6803

Diazinon is a widely used organophosphate insecticide that persists in agricultural runoff and poses risks to aquatic ecosystems and public health.In this study, we investigated the potential of a genetically engineered cyanobacterium, Synechocystis sp.PCC 6803, for efficient diazinon removal under varying environmental conditions.A phoU mutant lacking the negative regulator of the Pho regulon was employed to maintain constitutive phosphate uptake and metabolism independent of external phosphate availability.The phoU strain exhibited sustained expression of alkaline phosphatase (ALP), resulting in ALP activity 2.5-fold higher than that of the wild-type (WT).Under different phosphate concentrations (0-1.6 mM), phoU completely degraded diazinon (20 mg/l) within 11 days, with a degradation rate constant (k) up to 2.1-fold higher than WT under phosphate-replete conditions.Concurrently, phoU accumulated intracellular polyphosphate (poly-P) at levels up to four times higher than WT.Light intensity further modulated diazinon degradation and phosphate metabolism.Under high light intensity (2000 mol photons/m 2 /s), the phoU strain showed a 2.5-fold increase in diazinon degradation rate compared to WT, accompanied by a maximum poly-P accumulation of 10.95 mg/g FCW.Correlation analysis revealed a strong positive relationship between degradation rate and poly-P accumulation, indicating that organophosphate pesticide degradation is functionally linked to intracellular phosphate metabolism.These findings demonstrate that genetic deregulation of the Pho regulon enhances both diazinon degradation and phosphate assimilation, highlighting the phoU mutant as an effective cyanobacterial platform for organophosphate pesticide bioremediation under environmentally relevant conditions.