title: Stress response of Salmonella enterica serovar typhimurium to acidified nitrite.
abstract: The antimicrobial action of the curing agent sodium nitrite (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 used RNA sequencing to analyze the acidified-NaNO2 shock and adaptive responses of Salmonella enterica serovar Typhimurium, a frequent contaminant in raw meat, considering parameters relevant for the production of raw-cured sausages. Upon a 10-min exposure to 150 mg/liter 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. In contrast, genes involved in translation, transcription, replication, and motility were downregulated. The induction of stress tolerance and the reduction of cell proliferation obviously promote survival under harsh acidified-NaNO2 stress. The subsequent adaptive response was characterized by upregulation of NsrR-regulated genes and iron uptake systems and by downregulation 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 in the level of acid stress. Deletion of cadA, which encodes lysine decarboxylase, resulted in increased sensitivity to acidified NaNO2. Intracellular pH measurements using a pH-sensitive green fluorescent protein (GFP) variant showed that the cytoplasmic pH of S. Typhimurium in LB medium (pH 5.5) is decreased upon the addition of NaNO2. This study provides the first evidence that intracellular acidification is an additional antibacterial mode of action of acidified NaNO2.
authors.affiliation: Abteilung Mikrobiologie (ZIEL), Technische Universität München, Freising, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Mühlig
authors.affiliation: Lehrstuhl für Technische Mikrobiologie, Technische Universität München, Freising, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Behr
authors.affiliation: Abteilung Mikrobiologie (ZIEL), Technische Universität München, Freising, Germany Lehrstuhl für Mikrobielle Ökologie, Technische Universität München, Freising, Germany.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Scherer
authors.affiliation: Abteilung Mikrobiologie (ZIEL), Technische Universität München, Freising, Germany Lehrstuhl für Mikrobielle Ökologie, Technische Universität München, Freising, Germany stefanie.mueller@wzw.tum.de.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Müller-Herbst
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D002262:Carboxy-Lyases / Q000235:genetics* / Q000378:metabolism; D005511:Food Handling / Q000379:methods; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D005816:Genetic Complementation Test; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000494:pharmacology; D008461:Meat Products / Q000382:microbiology; D009154:Mutation; D015203:Reproducibility of Results; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D017423:Sequence Analysis, RNA; D012977:Sodium Nitrite / Q000494:pharmacology*; D013312:Stress, Physiological / Q000187:drug effects
chemical_list: D019344:Lactic Acid; D002262:Carboxy-Lyases; C021520:lysine decarboxylase; D012977:Sodium Nitrite
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