Biomimetic silicification enhances high-molecular-weight PAH biodegradation by stabilizing microalgae-bacteria consortium under acidic stress.

High-molecular-weight polycyclic aromatic hydrocarbons (HMW PAHs) are persistent pollutants whose biodegradation is strongly inhibited under acidic conditions. Here, a microalgae-bacteria consortium composed of Parachlorella kessleri and Paenibacillus illinoisensis was subjected to an integrated fabrication process comprising PDADMAC-assisted aggregation and nanosilicate deposition. Structural characterization confirmed sequential charge reversal, microbial aggregation, and formation of a silica-associated outer interface. Relative to the unmodified consortium, the fabricated group retained more chlorophyll, accumulated less reactive oxygen species, and maintained higher cytochrome P450 content under acid-PAH co-stress. PAH mass-balance analysis showed that biodegradation-associated transformation remained the dominant removal fraction, including an 84.44% biodegradation-associated fraction for benzo[a]pyrene at pH 3. Transcriptomic profiles further revealed reduced stress/repair investment together with preservation of energy and xenobiotic-degradation pathways. These multilevel results demonstrate that the complete PDADMAC-nanosilicate treatment stabilizes consortium function and sustains HMW-PAH transformation in a controlled acidic soil-extract system.