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Genome location dictates the transcriptional response to sub-inhibitory concentrations of PolC-inhibitors in Clostridium difficile

ABSTRACT: Clostridium difficile is a potentially lethal gut pathogen that causes nosocomial and community acquired infections. Limited treatment options and reports of reduced susceptibility to current treatment emphasize the necessity for novel antimicrobials. The DNA-polymerase of gram-positive organisms is an attractive target for the development of antimicrobials. ACX362E (N2-(3,4-Dichlorobenzyl)-7-(2-[1-morpholinyl]ethyl)guanine; MorE-DCBG) is a DNA polymerase inhibitor in pre-clinical development as a novel therapeutic against C. difficile infection. This synthetic purine shows preferential activity against C. difficile Pol IIIC over those of other organisms in vitro and is effective in an animal model of C. difficile infection. In this study we have determined its efficacy against a large collection of clinical isolates. At concentrations below the minimal inhibitory concentration, the presumed slowing (or stalling) of replication forks due to ACX362E leads to a growth defect. We have determined the transcriptional response of C. difficile to replication inhibition and observed an overrepresentation of up-regulated genes near the origin of replication in the presence of PolC-inhibitors, but not when cells were subjected to sub-inhibitory concentrations of other antibiotics. This phenomenon can be explained by a gene dosage shift, as we observed a concomitant increase in the ratio between origin-proximal versus terminus-proximal gene copy number upon exposure to PolC-inhibitors. Moreover, we show that certain genes differentially regulated under PolC-inhibition are controlled by the origin-proximal general stress response regulator sigma factor B. Together, these data suggest that genome location both directly and indirectly determines the transcriptional response to replication inhibition in C. difficile

ORGANISM(S): Clostridioides difficile

PROVIDER: GSE116503 | GEO | 2018/07/03

REPOSITORIES: GEO

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Project description:Clostridioides difficile (formerly Clostridium difficile) colonizes the gastrointestinal tract following disruption of the microbiota and can initiate a spectrum of clinical manifestations ranging from asymptomatic to life-threatening colitis. Following antibiotic treatment, luminal oxygen concentrations increase, exposing gut microbes to potentially toxic reactive oxygen species (ROS). Though typically regarded as a strict anaerobe, C. difficile can grow at low oxygen concentrations. How the bacterium adapts to a microaerobic environment and whether those responses to oxygen are conserved amongst strains is not entirely understood. Here, two C. difficile strains (630 and CD196) were cultured in 1.5% oxygen and the transcriptional response was evaluated via RNA-sequencing. During growth in a microaerobic environment, several genes predicted to protect against oxidative stress were upregulated, including ruberythrins and rubredoxins. Genes involved in metal homeostasis were positively correlated with increasing oxygen levels and were also amongst the most differentially transcribed. These included ferrous iron transporters (feo), a zinc transporter (zupT), and predicted siderophore transporters. To directly compare the transcriptional landscape between C. difficile strains, a ‘consensus-genome’ was generated. On the basis of the identified conserved genes, basal transcriptional differences as well as variations in the response to oxygen were evaluated. While several responses were similar between the strains, there were significant differences in the abundance of transcripts for amino acid and carbohydrate metabolism. Furthermore, homologous metal homeostasis genes were similarly transcribed, but the intracellular metal concentrations significantly varied both in an oxygen-dependent and independent manner. Overall, these results indicate that C. difficile adapts to grow in a low oxygen environment through transcriptional changes, though the specific strategy employed varies between strains.

Project description:A major risk factor for Clostridioides difficile infection (CDI) is the perturbation of the gut microbiota by antibiotic administration, and antibiotic therapy, the standard treatment option for CDI, exacerbates the imbalance of the gut microbiota, leading to a very high recurrent CDI (rCDI) incidence rate. Therefore, CDI treatment based on live biotherapeutic products (LBPs) has recently emerged for long-term CDI management and preventive treatment However, there is limited research and understanding of how these LBPs improve CDI symptoms, which raises the need to elucidate the therapeutic mechanisms of LBPs. To fill this knowledge gap, here, we holistically analyzed and investigated the mechanisms involved in the inhibitory effect of probiotics on C. difficile at the molecular level through a multiomics approach on screened strain from probiotics that inhibit C. difficile growth. First, Bifidobacterium species were co-cultured with C. difficile, and B. longum was screened based on its ability to inhibit the growth of C. difficile. Then, the antimicrobial activity of B. longum against C. difficile was confirmed by spot-on-lawn assay and organic acid quantification. Next, we performed proteomic and metabolomic analysis on C. difficile co-cultured with B. longum, and observed physiological changes associated with the inhibition of C. difficile growth and toxin production. It was found that lactate produced by B. longum up-regulated the lactate dehydrogenase complex of C. difficile, leading to a decrease in intracellular ATP synthesis and a subsequent decrease in (deoxy)ribonucleoside triphosphate synthesis. Furthermore, proteinaceous stress induced by B. longum was also identified through the up-regulation of ribosomal proteins, molecular chaperones, and chaperonins, and the down-regulation of translation-related proteins. Finally, we found that B. longum suppressed butyrate metabolism and toxin production by producing and replenishing proline consumed by C. difficile. Therefore, this study will not only expand our understanding of the mechanisms of probiotics' inhibition of C. difficile, but also contribute to the development of LBPs based on molecular mechanisms for treating CDI.

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Genome location dictates the transcriptional response to sub-inhibitory concentrations of PolC-inhibitors in Clostridium difficile

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