A TonB-dependent receptor constitutes the\xa0outer membrane transport system for a lignin-derived aromatic compound

Masaya Fujita,Shojiro Hishiyama,Naofumi Kamimura,Kosuke Mori,Hirofumi Hara,Eiji Masai

doi:10.1038/s42003-019-0676-z

Abstract

TonB-dependent receptors (TBDRs) mediate substrate-specific transport across the outer membrane, utilizing energy derived from the proton motive force transmitted from the TonB−ExbB−ExbD complex located in the inner membrane (TonB system). Although a number of TonB systems involved in the uptake of siderophores, vitamin B12 and saccharides have been identified, their involvement in the uptake and catabolism of aromatic compounds was previously unknown. Here, we show that the outer membrane transport of a biphenyl compound derived from lignin is mediated by the TonB system in a Gram-negative bacterium capable of degrading lignin-derived aromatic compounds, Sphingobium sp. strain SYK-6. Furthermore, we found that overexpression of the corresponding TBDR gene enhanced the uptake of this biphenyl compound, contributing to the improved rate of platform chemical production. Our results will provide an important basis for establishing engineered strains optimized for use in lignin valorisation.

Highlights

Pseudomonas aeruginosa PAO1 and a naphthalene porin of Pseudomonas fluorescens, respectively[11,12]
The upregulation of particular TonB-dependent receptors (TBDRs)-like genes has been observed in Sphingomonas wittichii RW1 and a Pseudomonas strain during their growth in the presence of dioxin and vanillin, respectively, evoking the possibility that TBDRs participate in the outer membrane transport and catabolism of aromatic compounds[16,17]
Based on the fact that SYK-6 specializes in the degradation of lignin-derived aromatic compounds, we predicted the involvement of TBDR genes in the outer membrane transport of aromatic compounds[23]

Summary

Introduction

Pseudomonas aeruginosa PAO1 and a naphthalene porin of Pseudomonas fluorescens, respectively[11,12]. The expression patterns of all TBDR genes in SYK-6 cells incubated in Wx minimal medium containing SEMP (10 mM sucrose, 10 mM glutamate, 20 mg l−1 methionine and 10 mM proline) in the presence and absence of lignin-derived aromatic compounds were investigated by DNA microarray analysis. We performed western blot analysis using anti-DdvT antibodies against total membrane fractions obtained from SYK-6, ddvT mutant (ΔddvT, Supplementary Fig. 2), and ddvR mutant (ΔddvR) cells grown with or without 1 mM DDVA.

Results

Conclusion