Newly discovered cyanobacteria Nostoc sp. PCC7120 for high efficiency biodegradation of thiamethoxam: Photosynthesis response, enzyme strategies, and molecular mechanisms.

Agricultural expansion has led to the accumulation of neonicotinoid pesticides in water and soil, which are habitats for widespread cyanobacteria. However, the cyanobacteria-neonicotinoids interaction mechanisms remain unclear. This study first explores Thiamethoxam (THX) biodegradation by Nostoc sp. PCC7120, elucidating cytochrome P450 (CYP450)-mediated THX metabolism. Nostoc sp. PCC7120 could remove THX completely within 6 days mainly via biodegradation (75 %). While THX stimulates cell growth, evidence (damaged thylakoid membranes, lowered electron transfer efficiency, reduced photosynthetic pigments, and altered key gene expression) shows it disrupts photosynthesis. Furthermore, THX degradation involved ring opening, nitrate reduction, de-chlorination, and N-dealkylation; molecular dynamics simulations revealed THX stably binding (32.38 kcal/mol) to CYP450's active site and primary degradation via hydroxylation and de-chlorination. Ecotoxicity assessments show desmethyl and urea metabolites are more toxic to non-target organisms and humans than the parent compound. This study elucidates THX removal mechanisms and environmental fate, highlighting cyanobacteria's potential in bioremediation for agricultural wastewater.