A Burkholderia thailandensis Acyl-Homoserine Lactone-Independent Orphan LuxR Homolog That Activates Production of the Cytotoxin Malleilactone.

TitleA Burkholderia thailandensis Acyl-Homoserine Lactone-Independent Orphan LuxR Homolog That Activates Production of the Cytotoxin Malleilactone.
Publication TypeJournal Article
Year of Publication2015
AuthorsTruong, TT, Seyedsayamdost, M, E Greenberg, P, Chandler, JR
JournalJ Bacteriol
Volume197
Issue21
Pagination3456-62
Date Published2015 Nov
ISSN1098-5530
Keywords4-Butyrolactone, Bacterial Proteins, Burkholderia, Gene Expression Regulation, Bacterial, Lactones, Promoter Regions, Genetic, Repressor Proteins, Trimethoprim
Abstract

UNLABELLED: Burkholderia thailandensis has three acyl-homoserine lactone (AHL) LuxR-LuxI quorum-sensing circuits and two orphan LuxR homologs. Orphans are LuxR-type transcription factors that do not have cognate LuxI-type AHL synthases. One of the orphans, MalR, is genetically linked to the mal gene cluster, which encodes enzymes required for production of the cytotoxic polyketide malleilactone. Under normal laboratory conditions the mal gene cluster is silent; however, antibiotics like trimethoprim induce mal transcription. We show that trimethoprim-dependent induction of the mal genes requires MalR. MalR has all of the conserved amino acid residues characteristic of AHL-responsive LuxR homologs, but in B. thailandensis, MalR activation of malleilactone synthesis genes is not responsive to AHLs. MalR can activate transcription from the mal promoter in E. coli without addition of AHLs or trimethoprim. Expression of malR in B. thailandensis is induced by trimethoprim. Our data indicate that MalR binds to a lux box-like element in the mal promoter and activates transcription of the mal genes in an AHL-independent manner. Antibiotics like trimethoprim appear to activate mal gene expression indirectly by somehow activating malR expression. MalR activation of the mal genes represents an example of a LuxR homolog that is not a receptor for an AHL quorum-sensing signal. Our evidence is consistent with the idea that mal gene activation depends solely on sufficient transcription of the malR gene.

IMPORTANCE: LuxR proteins are transcription factors that are typically activated by acyl-homoserine lactone (AHL) signals. We demonstrate that a conserved LuxR family protein, MalR, activates genes independently of AHLs. MalR is required for transcription of genes coding for synthesis of the cytotoxic polyketide malleilactone. These genes are not expressed when cells are grown under normal laboratory conditions. In laboratory culture, MalR induction of malleilactone requires certain antibiotics, such as trimethoprim, which increase malR expression by an unknown mechanism. At sufficient levels of malR expression, MalR functions independently of any external signal. Our findings show that MalR is an activator of the silent malleilactone biosynthesis genes and that MalR functions independently of AHLs.

DOI10.1128/JB.00425-15
Alternate JournalJ. Bacteriol.
PubMed ID26283771
PubMed Central IDPMC4621068
Grant ListP20 GM103638 / GM / NIGMS NIH HHS / United States
R01 GM059026 / GM / NIGMS NIH HHS / United States
GM-59026 / GM / NIGMS NIH HHS / United States