Enhanced phenanthrene degradation in microalgae-bacteria systems: Mechanistic roles of exogenous and indigenous...

This study investigates the synergistic mechanisms of phenanthrene (PHE) biodegradation using Chlorella vulgaris consortia with exogenous (EB) and indigenous (IB) bacteria. Results showed that both cooperative systems significantly enhanced algal growth and PHE removal, with biomass increasing by 17.2% (C.v-EB) and 75.0% (C.v-IB), and biodegradation rates reaching 75.3%-78.4%. Mechanistically, C.v-EB relied on enzymatic antioxidant responses (SOD and CAT) and a protein-rich extracellular polymeric substance (EPS) shield to mitigate oxidative stress. In contrast, C.v-IB exhibited superior resilience through non-enzymatic redox regulation (glutathione/thioredoxin systems) and the formation of a dense, biofilm-like EPS matrix supported by active transport genes (wzm/wzt). Metagenomic analysis revealed that C.v-IB possessed higher metabolic redundancy and energy production efficiency, organized into a coordinated "Degradation-Defense-Communication" genomic architecture via quorum sensing. Furthermore, both consortia expanded the metabolic landscape of PHE, effectively eliminating intermediate toxicity through divergent pathways. These findings provide a systematic framework for developing robust algal-bacterial biotechnologies for the remediation of polycyclic aromatic hydrocarbons in wastewater.