A TonB-dependent receptor regulates antifungal HSAF biosynthesis in Lysobacter.

Ruping Wang,Fengquan Liu,Shan-Ho Chou,Guoliang Qian,Youzhou Liu,Hongxia Liu,Huiyong Xu,Liangcheng Du

doi:10.1038/srep26881

Abstract

Lysobacter species are Gram-negative bacteria that are emerging as new sources of antibiotics, including HSAF (Heat Stable Antifungal Factor), which was identified from L. enzymogenes with a new mode of action. LesR, a LuxR solo, was recently shown to regulate the HSAF biosynthesis via an unidentified mechanism in L. enzymogenes OH11. Here, we used a comparative proteomic approach to identify the LesR targets and found that LesR influenced the expression of 33 proteins belonging to 10 functional groups, with 9 proteins belonging to the TBDR (TonB-Dependent Receptor) family. The fundamental role of bacterial TBDR in nutrient uptake motivates us to explore their potential regulation on HSAF biosynthesis which is also modulated by nutrient condition. Six out of 9 TBDR coding genes were individually in-frame deleted. Phenotypic and gene-expression assays showed that TBDR7, whose level was lower in a strain overexpressing lesR, was involved in regulating HSAF yield. TBDR7 was not involved in the growth, but played a vital role in transcribing the key HSAF biosynthetic gene. Taken together, the current lesR-based proteomic study provides the first report that TBDR7 plays a key role in regulating antibiotic (HSAF) biosynthesis, a function which has never been found for TBDRs in bacteria.

Highlights

TonB-dependent receptors (TBDRs) are a family of proteins that are located in the outer membrane of Gram-negative bacteria[1]
By a combination of proteomics, bioinformatics and genetic approaches, we discovered that a certain TBDR protein, whose level was affected by the lesR overexpression, played an important role in regulating the antibiotic HSAF biosynthesis in L. enzymogenes
But not deletion, of lesR in the wild-type OH11 was found to almost shut down the HSAF biosynthesis[29], we selected the lesR overexpression strain, as well as the wild-type OH11 possessing an empty vector as a control for 2-D gel proteome analysis to identify potential LesR targets in L. enzymogenes

Summary

Introduction

TonB-dependent receptors (TBDRs) are a family of proteins that are located in the outer membrane of Gram-negative bacteria[1]. The genus Lysobacter, belonging to the Xanthomonadaceae family, is a group of Gram-negative bacteria with several conserved features, such as high genomic G+C content (approximately 70%), flagella-independent twitching motility, production of abundant lytic enzymes, as well as generation of bioactive natural products[19,20,21]. By a combination of proteomics, bioinformatics and genetic approaches, we discovered that a certain TBDR protein, whose level was affected by the lesR overexpression, played an important role in regulating the antibiotic HSAF biosynthesis in L. enzymogenes. Our findings represent the first report about a novel functionality of TBDR proteins in bacteria

Methods

Results

Conclusion