Major facilitator superfamily transporter PhaT modulates the efflux and degradation of polycyclic aromatic hydrocarbons in Novosphingobium pentaromativorans US6-1

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent and toxic organic pollutants that are widely distributed in nature. Although catabolic pathways are essential for bacteria to effectively utilize PAHs, transporting PAHs and their intermediate metabolites across the bacterial cell envelope is a key factor in PAH catabolism and bacterial survival. In this study, we identified a major facilitator superfamily (MFS) transporter member, PhaT, in a PAH-degrading plasmid of Novosphingobium pentaromativorans US6-1. Evolutionary analyses indicate that PhaT analogs are widely distributed in PAH-degrading bacteria, including the genera Novosphingobium and Sphingobium. Interestingly, deletion of the phaT gene upregulated the levels of PAH-degrading enzymes and PAH-degrading gene expression, thereby accelerating phenanthrene biodegradation. Further studies demonstrated that a deficiency of PhaT impaired the efflux of phenanthrene and its benzene ring-containing intermediate metabolites. Furthermore, the deficiency of PhaT also promoted the biodegradation of naphthalene but not of benzo[a]pyrene. Molecular docking and site-directed mutagenesis revealed the essential roles of hydrophobic amino acids in the PhaT central cavity for binding to benzene ring-containing substrates. Collectively, these findings indicate that PhaT plays a pivotal role in facilitating the efflux of PAHs and their benzene ring-containing intermediate metabolites.