摘要：TonB-dependent transporters (TBDTs) mediate outer membrane transport of nutrients using the energy derived from proton motive force transmitted from the TonB–ExbB–ExbD complex localized in the inner membrane. Recently, we discovered
ddvT encoding a TBDT responsible for the uptake of a 5,5-type lignin-derived dimer in
Sphingobium sp. strain SYK-6. Furthermore, overexpression of
ddvT in an SYK-6-derivative strain enhanced its uptake capacity, improving the rate of platform chemical production. Thus, understanding the uptake system of lignin-derived aromatics is fundamental for microbial conversion-based lignin valorization. Here we examined whether multiple
tonB-,
exbB-, and
exbD-like genes in SYK-6 contribute to the outer membrane transport of lignin-derived aromatics. The disruption of
tonB2–
6 and
exbB3 did not reduce the capacity of SYK-6 to convert or grow on lignin-derived aromatics. In contrast, the introduction of the
tonB1–
exbB1–
exbD1–
exbD2 operon genes into SYK-6, which could not be disrupted, promoted the conversion of β-O-4-, β-5-, β-1-, β-β-, and 5,5-type dimers and monomers, such as ferulate, vanillate, syringate, and protocatechuate. These results suggest that TonB-dependent uptake involving the
tonB1 operon genes is responsible for the outer membrane transport of the above aromatics. Additionally,
exbB2/
tolQ and
exbD3/
tolR were suggested to constitute the Tol-Pal system that maintains the outer membrane integrity.
