Heavy metal-driven biochemical enhancement of dye degradation by bacterial consortia: a multi-scale statistical and spectroscopic investigation

This study evaluated the heavy metal-induced enhancement of azo dye degradation using three bacterial strains: <i>Acinetobacter</i> sp. SS1, <i>Acinetobacter baumannii</i> SS3, and <i>Bacillus cereus</i> SS2. Under normal monoculture (NM) conditions, dye degradation efficiencies ranged from 22.2% to 26.7%. Under 2.5% heavy metal stress, efficiencies increased to 32.8%-39.0%, indicating <i>a</i> ∼1.5-fold increase. The most significant improvement was observed in stress-adapted consortia, where degradation efficiencies ranged from 52.3% to 59.0%, representing a nearly 2.4-fold increase compared with those in NMs. Fourier-transform infrared analysis revealed more than 10 stress-specific functional groups, including nitriles, amides, and sulfonates, confirming metabolic reprogramming. Auto-aggregation reached a maximum of 41.6% in <i>B. cereus</i> SS2 after 16 h, while molecular docking of Dyp peroxidase (7YZT) and azoreductase (3W77) yielded binding energies of -24.7 kcal mol^-1, supporting high enzyme interaction stability. Phytotoxicity assays showed 100% seed germination and enhanced stem height (by ∼45%) in plants treated with stress-consortia-remediated effluent. Two-way analysis of variance yielded statistically significant results across treatment groups (<i>P</i> < 0.01), and principal component analysis showed distinct clustering of stress-consortia performance in the first principal component (PC₁ = 2.2693 for C1). These results confirm that microbial consortia preconditioned with metal stress exhibit significantly enhanced bioremediation capabilities in complex dye-contaminated systems.