Article

Sensing and Adaptation to Low pH Mediated by Inducible Amino Acid Decarboxylases in Salmonella

Laboratoire de Chimie Bactérienne, Institut de Microbiologie de la Méditerranée, CNRS (UPR-CNRS 9043), Marseille, France.
PLoS ONE (Impact Factor: 3.23). 07/2011; 6(7):e22397. DOI: 10.1371/journal.pone.0022397
Source: PubMed

ABSTRACT

During the course of infection, Salmonella enterica serovar Typhimurium must successively survive the harsh acid stress of the stomach and multiply into a mild acidic compartment within macrophages. Inducible amino acid decarboxylases are known to promote adaptation to acidic environments. Three low pH inducible amino acid decarboxylases were annotated in the genome of S. Typhimurium, AdiA, CadA and SpeF, which are specific for arginine, lysine and ornithine, respectively. In this study, we characterized and compared the contributions of those enzymes in response to acidic challenges. Individual mutants as well as a strain deleted for the three genes were tested for their ability (i) to survive an extreme acid shock, (ii) to grow at mild acidic pH and (iii) to infect the mouse animal model. We showed that the lysine decarboxylase CadA had the broadest range of activity since it both had the capacity to promote survival at pH 2.3 and growth at pH 4.5. The arginine decarboxylase AdiA was the most performant in protecting S. Typhimurium from a shock at pH 2.3 and the ornithine decarboxylase SpeF conferred the best growth advantage under anaerobiosis conditions at pH 4.5. We developed a GFP-based gene reporter to monitor the pH of the environment as perceived by S. Typhimurium. Results showed that activities of the lysine and ornithine decarboxylases at mild acidic pH did modify the local surrounding of S. Typhimurium both in culture medium and in macrophages. Finally, we tested the contribution of decarboxylases to virulence and found that these enzymes were dispensable for S. Typhimurium virulence during systemic infection. In the light of this result, we examined the genomes of Salmonella spp. normally responsible of systemic infection and observed that the genes encoding these enzymes were not well conserved, supporting the idea that these enzymes may be not required during systemic infection.

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    • "Decarboxylation of arginine, lysine and ornithine leads to the production of agmatine, cadaverine and putrescine, respectively. Both the arginine and lysine decarboxylase systems have been involved in survival at extremely acidic pH (Cirillo, Valdivia, Monack, & Falkow, 1998; Miller, Kukral, & Mekalanos, 1989; Shea, Hensel, Gleeson, & Holden, 1996; Vialla et al., 2011). The idea of Salmonella defenses responses could be employed in systems as polydiacetylene (PDA) to detect this pathogen so important to public health system. "
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    ABSTRACT: a b s t r a c t During the course of infection, Salmonella must successively survive the harsh acid stress of the stomach and multiply into a mild acidic compartment within macrophages. Inducible amino acid decarboxylases are known to promote adaptation to acidic environments, as lysine decarboxylation to cadaverine. The idea of Salmonella defenses responses could be employed in systems as polydiacetylene (PDA) to detect this pathogen so important to public health system. Beside that PDA is an important substance because of the unique optical property; that undergoes a colorimetric transitions by various external stimuli. Therefore 10,12-pentacosadyinoic acid (PCDA)/Sphingomyelin(SPH)/Cholesterol(CHO)/Lysine system was tested to determine the colorimetric response induced by Salmonella choleraesuis. PCDA/SPH/CHO/ Lysine vesicles showed a colour change even in low S. choleraesuis concentration present in laboratory conditions and in chicken meat. Thus, this work showed a PCDA/SPH/CHO/Lysine vesicle application to simplify routine analyses in food industry, as chicken meat industry.
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    • "Decarboxylation of arginine, lysine and ornithine leads to the production of agmatine, cadaverine and putrescine, respectively. Both the arginine and lysine decarboxylase systems have been involved in survival at extremely acidic pH (Cirillo, Valdivia, Monack, & Falkow, 1998; Miller, Kukral, & Mekalanos, 1989; Shea, Hensel, Gleeson, & Holden, 1996; Vialla et al., 2011). The idea of Salmonella defenses responses could be employed in systems as polydiacetylene (PDA) to detect this pathogen so important to public health system. "
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