Dataset Information

Probing the ArcA regulon under aerobic/ROS conditions in Salmonella enterica serovar Typhimurium.

ABSTRACT: Hydrogen peroxide (H?O?) is a reactive oxygen species (ROS), which is part of the oxidative burst encountered upon internalization of Salmonella enterica serovar Typhimurium (S. Typhimurium) by phagocytic cells. It has previously been established that, the ArcAB two-component system plays a critical role in ROS resistance, but the genes regulated by the system remained undetermined to date. We therefore investigated the ArcA regulon in aerobically growing S. Typhimurium before and after exposure to H?O? by querying gene expression and other physiological changes in wild type and ?arcA strains.In the ?arcA strain, expression of 292 genes showed direct or indirect regulation by ArcA in response to H?O?, of which 141were also regulated in aerobiosis, but in the opposite direction. Gene set enrichment analysis (GSEA) of the expression data from WT and ?arcA strains, revealed that, in response to H?O? challenge in aerobically grown cells, ArcA down regulated multiple PEP-PTS and ABC transporters, while up regulating genes involved in glutathione and glycerolipid metabolism and nucleotide transport. Further biochemical analysis guided by GSEA results showed that deletion of arcA during aerobic growth lead to increased reactive oxygen species (ROS) production which was concomitant with an increased NADH/NAD+ ratio. In absence of ArcA under aerobic conditions, H?O? exposure resulted in lower levels of glutathione reductase activity, leading to a decreased GSH (reduced glutathione)/GSSG (oxidized glutathione) ratio.The ArcA regulon was defined in 2 conditions, aerobic growth and the combination of peroxide treatment and aerobic growth in S. Typhimurium. ArcA coordinates a response that involves multiple aspects of the carbon flux through central metabolism, which ultimately modulates the reducing potential of the cell.

SUBMITTER: Morales EH

PROVIDER: S-EPMC3848847 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Probing the ArcA regulon under aerobic/ROS conditions in Salmonella enterica serovar Typhimurium.

Morales Eduardo H EH Collao Bernardo B Desai Prerak T PT Calderón Iván L IL Gil Fernando F Luraschi Roberto R Porwollik Steffen S McClelland Michael M Saavedra Claudia P CP

BMC genomics 20130917

<h4>Background</h4>Hydrogen peroxide (H₂O₂) is a reactive oxygen species (ROS), which is part of the oxidative burst encountered upon internalization of Salmonella enterica serovar Typhimurium (S. Typhimurium) by phagocytic cells. It has previously been established that, the ArcAB two-component system plays a critical role in ROS resistance, but the genes regulated by the system remained undetermined to date. We therefore investigated the ArcA regulon in aerobically growing S. Typhimurium before ...[more]

PMID: 24044554

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Project description:Salmonella enterica serovar Typhimurium (S. Typhimurium) is a Gram-negative pathogen that must successfully adapt to the broad fluctuations in the concentration of dissolved dioxygen encountered in the host. In Escherichia coli, ArcA (Aerobic Respiratory Control) helps the cells to sense and respond to the presence of dioxygen. The global role of ArcA in E. coli is well characterized; however, little is known about its role in anaerobically grown S. Typhimurium.We compared the transcriptional profiles of the virulent wild-type (WT) strain (ATCC 14028s) and its isogenic arcA mutant grown under anaerobic conditions. We found that ArcA directly or indirectly regulates 392 genes (8.5% of the genome); of these, 138 genes are poorly characterized. Regulation by ArcA in S. Typhimurium is similar, but distinct from that in E. coli. Thus, genes/operons involved in core metabolic pathways (e.g., succinyl-CoA, fatty acid degradation, cytochrome oxidase complexes, flagellar biosynthesis, motility, and chemotaxis) were regulated similarly in the two organisms. However, genes/operons present in both organisms, but regulated differently by ArcA in S. Typhimurium included those coding for ethanolamine utilization, lactate transport and metabolism, and succinate dehydrogenases. Salmonella-specific genes/operons regulated by ArcA included those required for propanediol utilization, flagellar genes (mcpAC, cheV), Gifsy-1 prophage genes, and three SPI-3 genes (mgtBC, slsA, STM3784). In agreement with our microarray data, the arcA mutant was non-motile, lacked flagella, and was as virulent in mice as the WT. Additionally, we identified a set of 120 genes whose regulation was shared with the anaerobic redox regulator, Fnr.We have identified the ArcA regulon in anaerobically grown S. Typhimurium. Our results demonstrated that in S. Typhimurium, ArcA serves as a transcriptional regulator coordinating cellular metabolism, flagella biosynthesis, and motility. Furthermore, ArcA and Fnr share in the regulation of 120 S. Typhimurium genes.

Project description:Enteric pathogens cycle between nutrient-rich host and nutrient-poor external environment. These pathogens compete for nutrients while cycling between host and external environment, and often experience starvation. In this context, we have studied the role of a global regulator (NtrC) of Salmonella Typhimurium. The ntrC knockout mutation caused extended lag phase (8 h) and slow growth in the minimal medium. In lag phase, the wild-type cells showed ~60-fold more expression of ntrC gene. Gene expression studies and biochemical assays showed that the extended lag phase and slow growth is due to slow metabolism, instead of nitrogen transport. Further, we observed that ntrC knockout mutation led extended lag phase and slow growth, made ΔntrC mutant unable to compete with wild-type S. Typhimurium in both static and fluctuating nutrient condition. In addition to this, ΔntrC knockout mutant was unable to survive long-term nitrogen starvation (150 days). The nutrient recycling assays and gene expression studies revealed that ntrC gene is essential for rapid recycling of nutrients from the dead cells. Moreover, in the absence of ntrC gene, magnesium limits the nutrient recycling efficiency of S. Typhimurium. Therefore, the ntrC gene, which is often studied with respect to nitrogen scavenging in a low nitrogen growing condition, is required even in the adequate supply of nitrogen to maintain optimal growth and fast exit from the lag phase. Hence, we conclude that, the ntrC expression is essential for competitive fitness of S. Typhimurium under the low and fluctuating nutrient condition. IMPORTANCE S. Typhimurium, both in host and external environment, faces enormous competition from other microorganisms. The competition may take place either in static or in fluctuating nutrient conditions. Thus, how S. Typhimurium survives under such overlapping stress conditions remained unclear. Therefore, using S. Typhimurium as model organism we report that a global regulator NtrC, found in enteric bacteria like Escherichia coli and Salmonella, activates the set of genes and operons involved in rapid adaptation and efficient nutrient recycling/scavenging. These properties enable cells to compete with other microbes under the characteristic feast-or-famine lifestyle of S. Typhimurium. Therefore, this work helps us to understand the starvation physiology of the enteric bacterial pathogen S. Typhimurium.

Dataset Information

Probing the ArcA regulon under aerobic/ROS conditions in Salmonella enterica serovar Typhimurium.

Publications

Probing the ArcA regulon under aerobic/ROS conditions in Salmonella enterica serovar Typhimurium.

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