Influence of growth substrate and contaminant mixtures on the degradation of BTEX and MTBE by Rhodococcus rhodochrous ATCC strain 21198

Identification of Potentially Toxic Transformation Products Produced in Polycyclic Aromatic Hydrocarbon Bioremediation Using Suspect and Non-Target Screening Approaches

Polycyclic aromatic hydrocarbons (PAHs) are a class of ubiquitous environmental contaminants that can be remediated through physical, chemical, or biological means. Treatment strategies can lead to the formation of PAH-transformation products (PAH-TPs) that, despite having the potential for adverse ecological and human health effects, are unregulated and understudied in environmental monitoring and remediation. Unavailability of reference standards for PAH-TPs limits the ability to identify PAH-TPs by targeted methods. This study utilized suspect and nontarget screening approaches to identify PAH-TPs produced by a bacterial culture, Rhodococcus rhodochrous ATCC 21198, using liquid chromatography-high resolution mass spectrometry. Open-source tools were used to predict biotransformation products, predict potential PAH-TP structures from mass spectra, and estimate health hazards of potential PAH-TPs. The workflow developed in this study allowed for the tentative identification of 16 PAH-TPs (confidence levels 2a to 3), seven of which were not previously detected by targeted analysis. Several new potential transformation pathways for our bacterial pure culture were suggested by the PAH-TPs, including carboxylation, sulfonation and up to three hydroxylation reactions. A computational toxicity assessment indicated that the PAH-TPs shared many hazard characteristics with their parent compounds, including genotoxicity and endocrine disruption, highlighting the importance of considering PAH-TPs in future PAH studies.

Heterogeneity in the Composition and Catabolism of Indigenous Microbiomes in Subsurface Soils Cocontaminated with BTEX and Chlorinated Aliphatic Hydrocarbons

The effectiveness of in situ bioremediation can be affected by an insufficient understanding of high site/soil heterogeneity, especially in cocontaminated soils and sediments. In this study, samples from multiple locations within a relatively small area (20 × 20 m2) contaminated with benzene, toluene, ethylbenzene, and xylene (BTEX) and chlorinated aliphatic hydrocarbons (CAHs) were compared to examine their physicochemical and microbial properties. Unsupervised clustering analysis of 16S rRNA gene amplicon and metagenome shotgun sequencing data indicates that the indigenous community differentiated into three distinct patterns. In Cluster 1, Pseudomonas, with multiple monooxygenases and glutathione S-transferase (GST), was enriched in samples contaminated with high concentrations of BTEX and CAHs. Cluster 2 contained a high fraction of cometabolic degraders. Cluster 3 was dominated by Ralstonia and organohalide-respiring bacteria (OHRBs) mediating the reductive dechlorination of CAHs. Significant differences in composition and function among microbiomes were attributed to the differential distribution of organic pollutants, even in such a small area. Incorporating genomic features with physicochemical data can significantly enhance the understanding of the heterogeneities in soil and their impacts on microbial communities, thereby providing valuable information for the optimization of bioremediation strategies.

PAH bioremediation with Rhodococcus rhodochrous ATCC 21198: Impact of cell immobilization and surfactant use on PAH treatment and post-remediation toxicity

Polycyclic aromatic hydrocarbons (PAHs) are prevalent environmental contaminants that are harmful to ecological and human health. Bioremediation is a promising technique for remediating PAHs in the environment, however bioremediation often results in the accumulation of toxic PAH metabolites. The objectives of this research were to demonstrate the cometabolic treatment of a mixture of PAHs by a pure bacterial culture, Rhodococcus rhodochrous ATCC 21198, and investigate PAH metabolites and toxicity. Additionally, the surfactant Tween ® 80 and cell immobilization techniques were used to enhance bioremediation. Total PAH removal ranged from 70-95% for fluorene, 44-89% for phenanthrene, 86-97% for anthracene, and 6.5-78% for pyrene. Maximum removal was achieved with immobilized cells in the presence of Tween ® 80. Investigation of PAH metabolites produced by 21198 revealed a complex mixture of hydroxylated compounds, quinones, and ring-fission products. Toxicity appeared to increase after bioremediation, manifesting as mortality and developmental effects in embryonic zebrafish. 21198's ability to rapidly transform PAHs of a variety of molecular structures and sizes suggests that 21198 can be a valuable microorganism for catalyzing PAH remediation. However, implementing further treatment processes to address toxic PAH metabolites should be pursued to help lower post-remediation toxicity in future studies.