Bacterial degradation of microcystins beyond parent-toxin loss: An evidence map of mechanisms, ecological constraints, and treatment validation.

Parent microcystin (MC) loss alone cannot distinguish bacterial transformation from sorption, retention, or analytical loss, and it does not establish product fate or residual hazard. We conducted a systematic evidence map with critical synthesis of bacteria-specific MC transformation, using Web of Science Core Collection, Scopus, and PubMed. After full-text assessment, 299 publications met the final operational strict evidence criteria. The literature was mapped across four separately coded, noncompensatory evidence dimensions, namely mechanistic resolution (M), environmental realism (E), toxicological completion (T), and treatment readiness (R). Product- or function-resolved evidence reached M2+ in 109/299 publications (36.5%), authentic environmental or treatment matrices reached E2+ in 72/299 (24.1%), complete-treated-material residual-hazard testing reached T2+ in 6/299 (2.0%), and the operational treatment-readiness threshold R2+ was met in 34/299 (11.4%). Only seven publications (2.3%) combined M2+ with E2+, and one publication (0.3%) met all four thresholds. No included publication met the operational M4 terminal carbon/nitrogen-fate criterion or the operational R4 sustained integrated-operation criterion used in this evidence map. MC-LR was represented in 92.3% of publications, limiting generalization across congeners. Within the included evidence base, the canonical mlr pathway was the only route for which convergent gene, enzyme, and product evidence resolved a multistep molecular sequence. Other aerobic, anaerobic, and community-mediated routes broaden observed transformation capacity but usually lack causal enzymes or complete product sequences. Engineering publications were concentrated in attached-growth filtration/BAC, immobilized systems, and other reactor-based designs, but process attribution, residual-hazard testing, and sustained operational evidence remain uneven. The resulting framework links each claim to the evidence needed to distinguish removal, transformation, detoxification, mineralization, and operationally supported risk-reduction claims.