Sphingomonads are well known for their ability to efficiently degrade polycyclic aromatic hydrocarbons (PAHs), but little is known about the mechanism of PAH uptake and transport across the cell membrane. RNA sequencing analysis of a sphingomonad, Novosphingobium pentaromativorans US6-1 showed that 38 TonB-dependent transporter (TBDT) genes were significantly upregulated under 5-ring PAH-benzo[a]pyrene (BaP) stress. In order to reveal whether TBDTs are involved in uptake and transport BaP in US6-1, the key TBDT genes were deleted to generate mutants. The results showed that the growth status of these mutants was not different from that of the wild-type strains, but the PAH degradation ability decreased, especially for the mutant strain Δtbdt-11, which did not encode the tbdt-11 gene. Meanwhile, the cell surface hydrophobicity (CSH) of Δtbdt-11 was found to be significantly lower than that of the wild-type strain under BaP stress. Furthermore, the transcriptional activity of genes encoding PAH degradative enzymes was found to be greatly reduced in Δtbdt-11. Confocal microscopy observations showed that US6-1 could transport BaP across the outer membrane, but this transport capacity was significantly reduced in Δtbdt-11 and wild-type US6-1 treated with PMF uncoupler, further confirming that the tbdt-11 gene was associated with PAH active transport.

Sphingomonads以其有效降解多环芳烃（PAHs）的能力而闻名，但对PAH吸收和跨细胞膜运输的机制知之甚少。鞘氨醇单胞菌新戊酸单胞菌US6-1的RNA测序分析表明，在5环PAH-苯并[a]（（BaP）胁迫下，38个TonB依赖性转运蛋白（TBDT）基因显着上调。为了揭示TBDT是否参与US6-1中BaP的吸收和转运，是关键的TBDT基因被删除以产生突变体。结果表明，这些突变体的生长状况不是来自野生型菌株不同，但PAH降解能力下降，特别是对于突变株Δ tbdt-11，其未在编码tbdt-11基因。同时，在BaP胁迫下，Δtbdt-11的细胞表面疏水性（CSH）明显低于野生型菌株。此外，发现在Δtbdt-11中编码PAH降解酶的基因的转录活性大大降低。共聚焦显微镜观察表明，US6-1可以转运BaP穿过外膜，但这种转运能力在Δ tbdt-11 和野生型US6-1与PMF解偶联剂处理，进一步确认tbdt-11基因与相关的PAH的活性转运。