Synergistic interaction between nitrifying bacteria and Enterobacter ludwigii enhances PAHs biodegradation in coal...

Polycyclic aromatic hydrocarbons (PAHs) are one of the most widespread organic pollutants. The methods to restore the natural environments contaminated with these substances include bioremediation based on PAH-degrading microorganisms. In coal dump soils, anaerobic conditions often develop, and therefore the ability of strains to perform anaerobic degradation of PAHs is a prerequisite for the successful remediation. The use of a synergistic microbial consortium capable of PAH degradation with the use of nitrates as electron acceptors in anaerobic conditions is a promising approach for environmental management of contaminated soils. The aim of the study was to assess the synergistic effects of nitrifying bacteria on the process of PAH degradation by denitrifying strain in coal dump soils. An enrichment culture of nitrifying microorganisms (38 % Nitrosomonas and Nitrolancea) was obtained from coal dump soils contaminated with PAHs. The enrichment culture demonstrated resistance to pyrene and phenanthrene and heavy metals. The isolated PAH-degrading bacterium Enterobacter ludwigii was able to reduce both nitrate and nitrite. Combined application of Enterobacter and the enrichment culture of nitrifiers significantly accelerated pyrene and phenanthrene decomposition by 30 % in contaminated coal dump soil, and the same was observed with addition of KNO₃ instead of enrichment culture highlighting the role of exogenous nitrate supply for PAHs degradation. Separate application of denitrifying strain Enterobacter ludwigii did not result in significant increase in PAHs degradation (less than 8 %). We propose a novel remediation approach, which involves the use of a consortium of PAH-degrading bacteria capable of denitrification and nitrifiers synthesizing electron acceptors to facilitate the remediation of PAH-contaminated soils.