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Stress response of Salmonella Typhimurium to acidified nitrite

ABSTRACT: The antimicrobial action of the curing agent NaNO2, which is added as a preservative to raw meat products, depends on its conversion to nitric oxide and other reactive nitrogen species under acidic conditions. In this study, we applied RNA-sequencing to analyze the acidified NaNO2 shock and adaptive response of Salmonella Typhimurium, a frequent contaminant in raw meat. Upon a 10 minute exposure to 150 mg/l NaNO2 in LB pH 5.5 acidified with lactic acid, genes involved in nitrosative stress protection together with several other stress related genes were induced. To the contrary, genes involved in translation, transcription, replication and motility were down-regulated. Induction of stress tolerance and reduction of cell proliferation obviously promote survival under harsh acidified NaNO2 stress. The subsequent adaptive response was characterized by up-regulation of NsrR-regulated genes and iron-uptake systems and down-regulation of genes involved in anaerobic respiratory pathways. Strikingly, amino acid decarboxylase systems, which contribute to acid tolerance, displayed increased transcript levels in response to acidified NaNO2. The induction of systems known to be involved in acid resistance indicates a nitrite mediated increase of acid stress.

ORGANISM(S): Salmonella enterica subsp. enterica serovar Typhimurium

PROVIDER: GSE57238 | GEO | 2014/08/25

SECONDARY ACCESSION(S): PRJNA246027

REPOSITORIES: GEO

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Project description:Dinoflagellates have evolved a nuclear organization unlike that of any other eukaryotic group. Recent studies find a predominance of post-transcriptional control of dinoflagellate gene expression. This study investigated regulation of the environmental stress response in the red tide dinoflagellate, Karenia brevis using an Agilent custom oligonucleotide microarray. K. brevis cultures were exposed to 5°C or 10°C heat shock, or three different sources of oxidative stress: 60 µM H2O2, 10 mM NaNO2, or 12 µM PbCl2 over acute time courses. Ribosomal genes, genes involved in RNA processing, translation, and chaperones were among the classes of genes consistently downregulated across treatments, although within these functional classes the same genes did not always respond to different stressors. Genes involved in the photosystem and mitochondrial and chloroplast ATP generation dominated the down-regulated genes. Heat shock and oxidative stress response genes were not induced under any treatment, even under conditions that resulted in decreased viability. We subsequently identified the presence of a trans-spliced leader sequence on many stress response gene transcripts, which suggests that they may be transcribed constitutively and their expression regulated at the level of translation. Cultures of were grown to mid-log phase. For each treatment, five replicate untreated control cultures and five replicate treated cultures were harvested at several time points following treatment. The following time courses were used: 5°C heat shock - 5, 15, 30, 60, and 240 min; 10°C heat shock - 60 min; 60 µM H2O2 - 5, 15, 30, 60, and 240 min; 10 mM NaNO2 -1, 4, and 7 hours; 12 µM PbCl2 -1, 4, and 7 hours. For each treatment, RNA was pooled from the controls and treated cultures at each timepoint. Two color arrays were then run comparing each the transcriptome at timepoint with the pooled control for that treatment. A technical dye swap array was run at each timepoint.

Project description:Comparative phenotype and transcriptome analyses were performed with Bacillus cereus ATCC 14579 exposed to acid down-shock to pH 5.5 set with different acidulants. When acidified with hydrochloric acid (HCl), growth was diminished, whereas 2 mM undissociated lactic acid (HL) or acetic acid (HAc) stopped growth without inactivation (bacteriostatic condition), and 15 mM undissociated HAc caused growth arrest and, finally, cell death, as reflected by a 3 to 4 log inactivation (bactericidal condition). Within the first 60 min after pH down-shock, the intracellular ATP levels of cultures shocked with HCl were increased. The bacteriostatic pH shocks did not result in increased nor decreased intracellular ATP levels, indicating that the high energy status within the stressed aerobically grown B. cereus cells could be maintained. In contrast, exposure to 15 mM undissociated HAc resulted in significant lower ATP levels, which was in accordance with the observed inactivation. The transcriptomic responses pH down-shocked cultures were studied in the same time frame. The analyses revealed general and specific responses coupled to the different phenotypes and the acidulant used. The general acid stress response, shown in all different pH shocks, involves modulation of pyruvate metabolism and an oxidative stress response. The shifts in pyruvate metabolism include induction dehydrogenases of a butanediol fermentation pathway under non-lethal acid stress conditions and of lactate, formate, and ethanol fermentation pathways under 15 mM HAc stress. Other 15 mM HAc-specific responses were induction of the alternative electron-transport systems, including cydAB, and fatty acid biosynthesis genes. Differences in gene expression for the bacteriostatic organic acid stress conditions compared to the growth-retarded inorganic stress condition indicated a more stringent oxidative stress response, including induction of an additional catalase gene and a gene encoding a Dps-like protein. Moreover, modulations in amino acid and oligopeptide transport were also found for the 2 mM HAc and HL shocks. HL-specific and HAc-specific responses both involve amino acid metabolism. Our study on the genome-wide responses of aerobically grown B. cereus pH 5.5 shocks provides a unique overview of the different responses induced by three acidulants relevant for food preservation.

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Stress response of Salmonella Typhimurium to acidified nitrite

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