Global Transcriptome and Mutagenic Analyses of the Acid Tolerance Response of Salmonella enterica Serovar Typhimurium

Abstract

b Salmonella enterica serovar Typhimurium (S. Typhimurium) is one of the leading causative agents of food-borne bacterial gastroenteritis. Swift invasion through the intestinal tract and successful establishment in systemic organs are associated with the adaptability of S. Typhimurium to different stress environments. Low-pH stress serves as one of the first lines of defense in mammalian hosts, which S. Typhimurium must efficiently overcome to establish an infection. Therefore, a better understanding of the molecular mechanisms underlying the adaptability of S. Typhimurium to acid stress is highly relevant. In this study, we have performed a transcriptome analysis of S. Typhimurium under the acid tolerance response (ATR) and found a large number of genes (ϳ47%) to be differentially expressed (more than 1.5-fold or less than ؊1.5-fold; P < 0.01). Functional annotation revealed differentially expressed genes to be associated with regulation, metabolism, transport and binding, pathogenesis, and motility. Additionally, our knockout analysis of a subset of differentially regulated genes facilitated the identification of proteins that contribute to S. Typhimurium ATR and virulence. Mutants lacking genes encoding the K ؉ binding and transport protein KdpA, hypothetical protein YciG, the flagellar hook cap protein FlgD, and the nitrate reductase subunit NarZ were significantly deficient in their ATRs and displayed varied in vitro virulence characteristics. This study offers greater insight into the transcriptome changes of S. Typhimurium under the ATR and provides a framework for further research on the subject. Salmonella enterica serovar Typhimurium is a neutralophilic, Gram-negative food-and waterborne pathogen that causes diseases ranging from gastroenteritis to systemic infection in humans. The intestinal tract of wild and domestic animals serves as a vehicle by which salmonellae find their way into humans through contaminated food and water. It has been estimated that globally this species accounts for about 80.3 million cases of food-borne gastroenteritis with about 1.5 million deaths (1). A large number of outbreaks have been linked to contaminated fruits and vegetables, including apples, mangoes, lettuce, tomatoes, celery, and unpasteurized juice (2). During host-pathogen interaction, Salmonella constantly encounters various stress conditions, such as changing pH, high osmotic pressure, low oxygen availability, and the presence of bile salts and antimicrobial peptides, that constantly test the adaptability of this pathogen. One such stress condition is low pH, and Salmonella confronts this on transit through the stomach, as well as during survival within the Salmonellacontaining vacuole (SCV) of phagocytic and nonphagocytic cells. Hence, the ability of Salmonella to perceive low-pH environments and respond to such stress is crucial for its survival and pathogenicity.The mechanism by which S. Typhimurium senses acidic environments and adapts to survive under low pH is termed the acid tolerance response (ATR) (3-...

The Hha-TomB Toxin-Antitoxin System Shows Conditional Toxicity and Promotes Persister Cell Formation by Inhibiting Apoptosis-Like Death in S. Typhimurium

“…A similar mechanism may operate in S. Typhimurium. In the data set reported by Ryan et al 31,. Hha is upregulated almost 6 folds under acid challenge31.…”

“…In the data set reported by Ryan et al 31,. Hha is upregulated almost 6 folds under acid challenge31. Furthermore, Hha over expression was accompanied by upregulation of most of the proteases such as ClpA, ClpP, ClpX and Lon as well as phage proteins31.…”

“…Hha is upregulated almost 6 folds under acid challenge31. Furthermore, Hha over expression was accompanied by upregulation of most of the proteases such as ClpA, ClpP, ClpX and Lon as well as phage proteins31. Thus it is apparent that similar to biofilms, Hha expression is upregulated under acid stress resulting in the activation of proteases and phage proteins, causing cell lysis.…”

“…Wild type S. Typhimurium SB30035 and its isogenic mutants were grown in Luria Bertani (LB) medium (10 g/L Bacto tryptone, 5 g/L Bacto yeast extract, 5 g/L NaCl, HiMedia, India) or minimal E glucose medium (minimal EG) containing MgSO 4 .7H 2 O (200 mg), citric acid.H 2 O (2 g), K 2 HPO 4 (10 g), NaH 2 PO 4 (1.75 g), (NH 4 ) 2 HPO 4 (1.75 g) in 1 L of Milli-Q water, adjusted to pH 7.536. The minimal medium was supplemented with 0.4% dextrose and 0.1% casein hydrolysate (both 0.22 μm filtered).…”

“…Survival under acid stress was analysed by a slightly modified procedure described previously36. Briefly, bacterial strains were grown overnight in minimal media (pH7.5) supplemented with appropriate antibiotics at 37 °C.…”