Malleilactone Is a Burkholderia pseudomallei Virulence Factor Regulated by Antibiotics and Quorum Sensing

Abstract

, the causative agent of melioidosis, encodes almost a dozen predicted polyketide (PK) biosynthetic gene clusters. Many of these are regulated by LuxR-I-type acyl-homoserine (AHL) quorum-sensing systems. One of the PK gene clusters, the gene cluster, is conserved in the close relative The genes code for the cytotoxin malleilactone and are regulated by a genetically linked LuxR-type transcription factor, MalR. Although AHLs typically interact with LuxR-type proteins to modulate gene transcription, the MalR does not appear to be an AHL receptor. Here, we characterize the genes and MalR in We use chemical analyses to demonstrate that the genes code for malleilactone. Our results show that MalR and the genes contribute to the ability of to kill In , antibiotics like trimethoprim can activate MalR by driving transcription of the genes, and we demonstrate that some of the same antibiotics induce expression of We also demonstrate that MalR does not respond directly to AHLs. Our results suggest that MalR is indirectly repressed by AHLs, possibly through a repressor, ScmR. We further show that malleilactone is a virulence factor and provide the foundation for understanding how malleilactone contributes to the pathology of melioidosis infections. Many bacterially produced polyketides are cytotoxic to mammalian cells and are potentially important contributors to pathogenesis during infection. We are interested in the polyketide gene clusters present in , which causes the often-fatal human disease melioidosis. Using knowledge gained by studies in the close relative, we show that one of the polyketide biosynthetic clusters produces a cytotoxic polyketide, malleilactone. Malleilactone contributes to virulence in a infection model and is regulated by an orphan LuxR family quorum-sensing transcription factor, MalR. Our studies demonstrate that malleilactone biosynthesis or MalR could be new targets for developing therapeutics to treat melioidosis.

ScmR, a global regulator of gene expression, quorum sensing, pH homeostasis, and virulence inBurkholderia thailandensis

“…10). However, we observed no difference in the transcription of the mal gene cluster, which encodes the principal enzymes responsible for malleilactone biosynthesis (15, 34), between the B. thailandensis E264 wild-type and the scmR -mutant strains, suggesting that ScmR is not necessarily involved in the production of the cytotoxin malleilactone. Any negative effect of ScmR on malleilactone biosynthesis in vivo is currently unknown.…”

“…S1 ). Accordingly, Klaus et al (34) and Majerczyk et al (20) demonstrated that the expression of scmR in B. pseudomallei Bp82 and B. mallei GB8 is stimulated by QS, respectively. Burkholderia cenocepacia J2315 also possesses an scmR homologue, which was shown to be QS-controlled in B. cenocepacia K56-2 (35), but no putative lux box sequence was found in its promoter region (36).…”

“…The cytotoxin malleilactone was reported to contribute to virulence of both B. thailandensis E264 and B. pseudomallei Bp82 (15, 34). Interestingly, a Δ scmR mutant of B. thailandensis E264, which overproduces malleilactone, is more virulent toward the C. elegans nematode model host in comparison with the wild-type strain (26).…”

“…While the pathogenicity of B. multivorans ATCC 17616 in the Galleria mellonella larvae model of infection is apparently not regulated by the ScmR homologue LdhR (37), the loss of ScmR in both B. thailandensis E264 and B. pseudomallei Bp82 resulted in hypervirulence toward the model host C. elegans (26, 34). In addition, Melanson et al (38) demonstrated that the rice pathogen B. glumae 336gr-1 ScmR homologue, called NtpR, is a negative regulator of toxoflavin production, which is considered the primary virulence factor of B. glumae , suggesting that similarly to the B. thailandensis E264 and B. pseudomallei Bp82 ScmR homologues, NtpR influences virulence.…”

“…In addition, Melanson et al (38) demonstrated that the rice pathogen B. glumae 336gr-1 ScmR homologue, called NtpR, is a negative regulator of toxoflavin production, which is considered the primary virulence factor of B. glumae , suggesting that similarly to the B. thailandensis E264 and B. pseudomallei Bp82 ScmR homologues, NtpR influences virulence. In B. thailandensis and B. pseudomallei , ScmR was proposed to modulate the infection process by repressing the biosynthesis of malleilactone (26, 34). We demonstrated that ScmR of B. thailandensis E264 contributes to pathogenicity using the D. melanogaster host model (Fig.…”