Antagonistic effects during phenanthrene and pyrene co-degradation by Pseudoxanthomonas: Pathway competition and substrate preference

The biodegradation of polycyclic aromatic hydrocarbons (PAHs) involves complex metabolic interactions among multiple degradation pathways. However, how interactions among different pathways influence the overall degradation efficiency remains poorly understood. In this study, Pseudoxanthomonas sp. G3, an efficient degrader of phenanthrene (PHE) and pyrene (PYR), was used to investigate pathway interactions under mixed-PAH conditions. Genomic and metabolomic analyses revealed that strain G3 degrades PHE and PYR through three pathways: the phthalate pathway (with phthalic acid as the dead-end product), a shared catechol degradation pathway, and the benzoate degradation pathway. Notably, PYR induced the benzoate degradation pathway, representing a previously unreported metabolism of PYR by bacteria. Integrated analyses revealed that PHE inhibits PYR degradation via dual mechanisms. Specifically, PHE preferentially utilizes the PYR-induced benzoate degradation pathway, thereby diverting metabolic flux and impeding PYR degradation. Moreover, the benzoate degradation pathway further inhibits the catechol degradation pathway, intensifying suppression of PYR degradation. These findings elucidate mechanistic insights into the interactions among the biodegradation pathways under mixed-PAH stress and provide a theoretical basis for targeted improvement of the efficiency and predictability of mixed-PAH degradation.