Research progress on polycyclic aromatic hydrocarbons degrading bacteria and their applications

Polycyclic aromatic hydrocarbons (PAHs) are a group of pollutants widely distributed in the environment and have ecological and environmental toxicity effects. Therefore, the remediation and restoration of PAHs-contaminated sites have received significant attention. Biodegradation is one of the essential technologies for removing PAHs; however, it still faces limitations such as low degradation efficiency and long degradation periods. The common PAHs-degrading bacteria and their degradation mechanisms were summarized, focusing on discussing the research progress and limitations of applying them to real contaminated sites. The results showed that PAHs-degrading bacteria mainly included genus Acinetobacter, Mycobacterium, and Pseudomonas. White-rot fungi were common fungi that degraded PAHs. Compared to individual strains, bacterial consortia exhibited superior PAH degradation capability. For PAHs such as naphthalene, phenanthrene and pyrene, the degradation process involved ring opening catalyzed by enzymes encoded by PAHs degradation genes (e.g., nah gene cluster), followed by stepwise oxidation, ultimately leading to complete degradation through the salicylic acid or phthalic acid pathway entering the tricarboxylic acid cycle. The degradation of benzoapyrene produced intermediate products, including alcohols, aldehydes, and acids. However, its complete degradation pathway was yet to be identified. Studies on PAHs degradation bacteria were mainly confined to laboratory conditions, and there was a lack of verification in real contaminated soils. In application, the activity of degrading bacteria and the efficiency of PAHs removal were influenced by various environmental factors, including temperature, pH, oxygen levels, and soil organic matter content. In addition, some cases utilized biological stimulation and/or bioaugmentation to significantly improve the bioremediation of PAH-contaminated sites. Nevertheless, the application must overcome multiple limiting factors, including reduced degrading bacteria activity, failed integration with multiple technologies, and high environmental risks and costs. Further researches should include the mechanisms of PAHs biodegradation under conditions with combined pollution and the presence of indigenous microorganisms, the regulation of physiological characteristics of degrading bacteria, and the development of novel materials. Furthermore, promoting the application of PAHs-degrading bacteria in real contaminated sites should be strengthened to achieve efficient, economical, and sustainable control of PAHs contamination