Degradation of chrysene by Rhodococcus pyridinivorans C7 isolated from earthworm gut - Deciphering microbial...

This study investigates the degradation of chrysene (a priority polycyclic aromatic hydrocarbon) by Rhodococcus pyridinivorans C7, isolated from the gut of Perionyx excavatus after 60 days acclimatization in petroleum-contaminated soil. After six days of incubation, strain C7 exhibited notable enzymatic activities, with catechol 1,2-dioxygenase (1.72 ± 0.14 U/mL) and catechol 2,3-dioxygenase (2.26 ± 0.19 U/mL). The strain achieved up to 75 % degradation of chrysene (40 mg/L) within this period. Gas chromatography-mass spectrometry analysis identified dibutyl phthalate as an intermediate product on day 2 and phenol 2,6-di-tert-butyl on days 4 and 6. Cytotoxicity assays revealed that the initial byproduct was highly toxic (IC₅₀ = 0.19 µg/mL), whereas the final metabolite exhibited markedly reduced toxicity (IC₅₀ = 19 µg/mL), indicating detoxification. Comparative genomics using Mauve software revealed strong genomic synteny between strain C7 and other PAH-degrading Rhodococcus species. Metagenomic analysis of earthworm gut microbiomes under different treatment - control (EG-C), petroleum contaminated (EG-P) and fly ash (EG-F) identified Proteobacteria as the predominant phylum with relative abundance of 21.17 %, 33.3 %, and 34.53 % respectively. Notably, the Rhodococcus genus exhibited a 1.46-fold and 1.42-fold increase in EG-P and EG-F, respectively compared to EG-C. R. pyridinivorans was detected in both EG-P and EG-F gut samples confirming its isolation through the earthworm gut. These results demonstrate that environmental perturbations can drive distinct shifts in gut microbial composition, enriching for hydrocarbon-degrading taxa. Understanding such adaptive microbial communities provides valuable insights for developing sustainable bioremediation strategies and identifying novel microbes for environmental cleanup.