An official website of the United States government
Abstract One of the most commonly prescribed antibiotics againstBurkholderiainfections is co‐trimoxazole, a cocktail of trimethoprim and sulfamethoxazole. Trimethoprim elicits an upregulation of themalgene cluster, which encodes proteins involved in synthesis of the cytotoxic polyketide malleilactone; trimethoprim does so by increasing expression of themalRgene, which encodes the activator MalR. We report thatB. thailandensisgrown on trimethoprim exhibited increased virulence againstCaenorhabditis elegans. This enhanced virulence correlated with an increase in expression of themalgene cluster. Notably, inhibition of xanthine dehydrogenase by addition of allopurinol led to similar upregulation ofmalAandmalR, with addition of trimethoprim or allopurinol also resulting in an equivalent intracellular accumulation of xanthine. Xanthine is a ligand for the transcription factor MftR that leads to attenuated DNA binding, and we show using chromatin immunoprecipitation that MftR binds directly tomalR. Our gene expression data suggest thatmalRexpression is repressed by both MftR and by a separate transcription factor, which also responds to a metabolite that accumulates on exposure to trimethoprim. Since allopurinol elicits a similar increase inmalR/malAexpression as trimethoprim, we suggest that impaired purine homeostasis plays a primary role in trimethoprim‐mediated induction ofmalRand in turnmalA.
more »
« less
Similar solutions to a common challenge: regulation of genes encoding Ralstonia solanacearum xanthine dehydrogenase
ABSTRACT The stringent response involves accumulation of (p)ppGpp, and it ensures that survival is prioritized. Production of (p)ppGpp requires purine synthesis, and upregulation of an operon that encodes the purine salvage enzyme xanthine dehydrogenase (Xdh) has been observed during stringent response in some bacterial species, where direct binding of ppGpp to a TetR-family transcription factor is responsible for increased xdh gene expression. We show here that the plant pathogen Ralstonia solanacearum has a regulatory system in which the LysR-family transcription factor XanR controls expression of the xan operon; this operon encodes Xdh as well as other enzymes involved in purine salvage, which favor accumulation of xanthine. XanR bound upstream of the xan operon, a binding that was attenuated on addition of either ppGpp or cyclic di-guanosine monophosphate (c-di-GMP). Using a reporter in which enhanced green fluorescent protein (EGFP) is expressed under control of a modified xan promoter, XanR was shown to repress EGFP production. Our data suggest that R. solanacearum features a regulatory mechanism in which expression of genes encoding purine salvage enzymes is controlled by a transcription factor that belongs to a different protein family, yet performs similar regulatory functions.
more »
« less
- Award ID(s):
- 1714219
- PAR ID:
- 10219127
- Date Published:
- Journal Name:
- FEMS Microbiology Letters
- Volume:
- 368
- Issue:
- 4
- ISSN:
- 1574-6968
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The genusVibrioincludes serious human pathogens, and mollusks are a significant reservoir for species such asV.vulnificus.Vibriospecies encode PecS, a member of the multiple antibiotic resistance regulator (MarR) family of transcription factors;pecSis divergently oriented topecM, which encodes an efflux pump. We report here thatVibriospecies feature frequent duplications ofpecS-pecMgenes, suggesting evolutionary pressures to respond to distinct environmental situations. The singleV.vulnificusPecS binds two sites within thepecS-pecMintergenic region with Kd = 0.3 ± 0.1 nM, a binding that is attenuated by the ligands xanthine and urate, except when promoter DNA is saturated with PecS. A unique target is found in the intergenic region between genes encoding the nitric oxide sensing transcription factor, NsrR, andnod; thenod-encoded nitric oxide dioxygenase is important for preventing nitric oxide stress. Reporter gene assays show that PecS-mediated repression of gene expression can be relieved in presence of ligand. Since xanthine and urate are produced as part of the oxidative burst during host defenses and under molluscan hypoxia, we propose that these intermediates in the host purine degradation pathway function to promote bacterial survival during hypoxia and oxidative stress.more » « less
-
Comstock, Laurie E. (Ed.)ABSTRACT Burkholderia thailandensis is a member of the Burkholderia pseudomallei complex. It encodes the transcription factor MftR, which is conserved among the more pathogenic Burkholderia spp. and previously shown to be a global regulator of gene expression. We report here that a B. thailandensis strain in which the mftR gene is disrupted is more virulent in both Caenorhabditis elegans and onion. The Δ mftR strain exhibits a number of phenotypes associated with virulence. It is more proficient at forming biofilm, and the arcDABC gene cluster, which has been linked to anaerobic survival and fitness within a biofilm, is upregulated. Swimming and swarming motility are also elevated in Δ mftR cells. We further show that MftR is one of several transcription factors which control production of the siderophore malleobactin. MftR binds directly to the promoter driving expression of mbaS , which encodes the extracytoplasmic function sigma factor MbaS that is required for malleobactin production. Malleobactin is a primary siderophore in B. thailandensis as evidenced by reduced siderophore production in mbaS ::Tc cells, in which mbaS is disrupted. Expression of mbaS is increased ~5-fold in Δ mftR cells, and siderophore production is elevated. Under iron-limiting conditions, mbaS expression is increased ~150-fold in both wild-type and Δ mftR cells, respectively, reflecting regulation by the ferric uptake regulator (Fur). The mbaS expression profiles also point to repression by a separate, ligand-responsive transcription factor, possibly ScmR. Taken together, these data indicate that MftR controls a number of phenotypes, all of which promote bacterial survival in a host environment. IMPORTANCE Bacterial pathogens face iron limitation in a host environment. To overcome this challenge, they produce siderophores, small iron-chelating molecules. Uptake of iron-siderophore complexes averts bacterial iron limitation. In Burkholderia spp., malleobactin or related compounds are the primary siderophores. We show here that genes encoding proteins required for malleobactin production in B. thailandensis are under the direct control of the global transcription factor MftR. Repression of gene expression by MftR is relieved when MftR binds xanthine, a purine metabolite present in host cells. Our work therefore identifies a mechanism by which siderophore production may be optimized in a host environment, thus contributing to bacterial fitness.more » « less
-
null (Ed.)The microbial ars operon encodes the primary bacterial defense response to the environmental toxicant, arsenic. An important component of this operon is the arsR gene, which encodes ArsR, a member of the family of proteins categorized as DNA-binding transcriptional repressors. As currently documented, ArsR regulates its own expression as well as other genes in the same ars operon. This study examined the roles of four ArsR proteins in the well-developed model Gram-negative bacterium Agrobacterium tumefaciens 5A. RNASeq was used to compare and characterize gene expression profiles in ± arsenite-treated cells of the wild-type strain and in four different arsR mutants. We report that ArsR-controlled transcription regulation is truly global, extending well beyond the current ars operon model, and includes both repression as well as apparent activation effects. Many cellular functions are significantly influenced, including arsenic resistance, phosphate acquisition/metabolism, sugar transport, chemotaxis, copper tolerance, iron homeostasis, and many others. While there is evidence of some regulatory overlap, each ArsR exhibits its own regulatory profile. Furthermore, evidence of a regulatory hierarchy was observed; i.e. ArsR1 represses arsR4 , ArsR4 activates arsR2 , and ArsR2 represses arsR3 . Additionally and unexpectedly, aioB (arsenite oxidase small subunit) expression was shown to be under partial positive control by ArsR2 and ArsR4. Summarizing, this study demonstrates the regulatory portfolio of arsenite-activated ArsR proteins and includes essentially all major cellular functions. The broad bandwidth of arsenic effects on microbial metabolism assists in explaining and understanding the full impact of arsenic in natural ecosystems, including the mammalian gut.more » « less
-
Stress and starvation causes bacterial cells to activate the stringent response. This results in down-regulation of energy-requiring processes related to growth, as well as an upregulation of genes associated with survival and stress responses. Guanosine tetra- and pentaphosphates (collectively referred to as (p)ppGpp) are critical for this process. In Gram-positive bacteria, a main function of (p)ppGpp is to limit cellular levels of GTP, one consequence of which is reduced transcription of genes that require GTP as the initiating nucleotide, such as rRNA genes. In Streptomycetes, the stringent response is also linked to complex morphological differentiation and to production of secondary metabolites, including antibiotics. These processes are also influenced by the second messenger c-di-GMP. Since GTP is a substrate for both (p)ppGpp and c-di-GMP, a finely tuned regulation of cellular GTP levels is required to ensure adequate synthesis of these guanosine derivatives. Here, we discuss mechanisms that operate to control guanosine metabolism and how they impinge on the production of antibiotics in Streptomyces species.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/femsle/fnab022
