Biodegradation of High-Molecular-Weight PAHs in Polluted Mangrove Sediments Using Indigenous Microflora and Exogenous Strains Rhodococcus erythropolis and Bacillus subtilis

Mangroves are highly productive coastal ecosystems, yet they are heavily exposed to pollution by polycyclic aromatic hydrocarbons (PAHs), particularly high-molecular-weight compounds such as pyrene and fluoranthene. These recalcitrant contaminants exhibit high toxicity and persist in the environment, threatening microbial biodiversity and the ecological stability of sediments. This study aims to assess the biodegradation potential of pyrene and fluoranthene in contaminated mangrove sediments by comparing the efficiency of the indigenous microflora with that of exogenous strains (Rhodococcus erythropolis and Bacillus subtilis), and to optimize degradation through bioaugmentation and biostimulation using nutrient amendments. Sediments were artificially spiked with 10,000 mg·kg⁻¹ of pyrene or fluoranthene. Microcosms under sterile and non-sterile conditions were established to evaluate, over five weeks, the biodegradation performance of the endogenous bacterial consortium, exogenous strains, biostimulation (compost), and their combinations. The results revealed significant PAH degradation by the indigenous microflora (45–52% after five weeks). Exogenous strains enhanced degradation rates, reaching 58% for B. subtilis and 63% for R. erythropolis . The combined application of bioaugmentation and biostimulation yielded the highest degradation levels, with 75% for the endogenous consortium and up to 78% for R. erythropolis . Statistical analyses confirmed that these differences were significant compared with sterile and non-sterile controls. The synergistic exploitation of indigenous microflora and exogenous strains, combined with nutrient amendments, constitutes an effective strategy for the bioremediation of mangrove sediments contaminated with high-molecular-weight PAHs. These findings provide a robust foundation for developing pollution-control technologies adapted to tropical coastal ecosystems.