Glutamate decarboxylase-dependent acid resistance in Brucella spp.: distribution and contribution to fitness under extremely acidic conditions.
Brucella is an expanding genus of major zoonotic pathogens, including at least 10 genetically very close species occupying a wide range of niches from soil to wildlife, livestock, and humans. Recently, we have shown that in the new species Brucella microti, the glutamate decarboxylase (Gad)-dependent system (GAD system) contributes to survival at a pH of 2.5 and also to infection in mice by the oral route. In order to study the functionality of the GAD system in the genus Brucella, 47 isolates, representative of all known species and strains of this genus, and 16 strains of the closest neighbor genus, Ochrobactrum, were studied using microbiological, biochemical, and genetic approaches. In agreement with the genome sequences, the GAD system of classical species was not functional, unlike that of most strains of Brucella ceti, Brucella pinnipedialis, and newly described species (B. microti, Brucella inopinata BO1, B. inopinata-like BO2, and Brucella sp. isolated from bullfrogs). In the presence of glutamate, these species were more acid resistant in vitro than classical terrestrial brucellae. Expression in trans of the gad locus from representative Brucella species in the Escherichia coli MG1655 mutant strain lacking the GAD system restored the acid-resistant phenotype. The highly conserved GAD system of the newly described or atypical Brucella species may play an important role in their adaptation to acidic external and host environments. Furthermore, the GAD phenotype was shown to be a useful diagnostic tool to distinguish these latter Brucella strains from Ochrobactrum and from classical terrestrial pathogenic Brucella species, which are GAD negative.
Université Montpellier, Centre d'Études d'Agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier, France CNRS, UMR 5236, CPBS, Montpellier, France.
Maria Alessandra
MA
Damiano
Istituto Pasteur-Fondazione Cenci Bolognetti, Dipartimento di Scienze e Biotecnologie Medico-Chirurgiche, Sapienza Università di Roma, Latina, Italy.
Daniela
D
Bastianelli
Federal Institute for Risk Assessment, Berlin, Germany.
Sascha
S
Al Dahouk
Université Montpellier, Centre d'Études d'Agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier, France CNRS, UMR 5236, CPBS, Montpellier, France.
Stephan
S
Köhler
INRA, UMR1282 Infectiologie et Santé Publique, Nouzilly, France Université François Rabelais de Tours, UMR1282 Infectiologie et Santé Publique, Tours, France.
Axel
A
Cloeckaert
Istituto Pasteur-Fondazione Cenci Bolognetti, Dipartimento di Scienze e Biotecnologie Medico-Chirurgiche, Sapienza Università di Roma, Latina, Italy daniela.debiase@uniroma1.it alessandra.occhialini@cpbs.cnrs.fr.
Daniela
D
De Biase
Université Montpellier, Centre d'Études d'Agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier, France CNRS, UMR 5236, CPBS, Montpellier, France daniela.debiase@uniroma1.it alessandra.occhialini@cpbs.cnrs.fr.
Alessandra
A
Occhialini
D000143:Acids / Q000378:metabolism* / Q000633:toxicity*; D000818:Animals; D002002:Brucella / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D003001:Cloning, Molecular; D004361:Drug Tolerance; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005968:Glutamate Decarboxylase / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D051379:Mice; D042041:Ochrobactrum / Q000187:drug effects / Q000201:enzymology; D011892:Rana catesbeiana
D000143:Acids; D018698:Glutamic Acid; D005968:Glutamate Decarboxylase