AUTHOR=Freddi Luca , Damiano Maria A. , Chaloin Laurent , Pennacchietti Eugenia , Al Dahouk Sascha , Köhler Stephan , De Biase Daniela , Occhialini Alessandra 

TITLE=The Glutaminase-Dependent System Confers Extreme Acid Resistance to New Species and Atypical Strains of Brucella

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.02236

DOI=10.3389/fmicb.2017.02236

ISSN=1664-302X

ABSTRACT=<p>Neutralophilic bacteria have developed specific mechanisms to cope with the acid stress encountered in environments such as soil, fermented foods, and host compartments. In <italic>Escherichia coli</italic>, the glutamate decarboxylase (Gad)-dependent system is extremely efficient: it requires the concerted action of glutamate decarboxylase (GadA/GadB) and of the glutamate (Glu)/γ-aminobutyrate antiporter, GadC. Notably, this system is operative also in new strains/species of <italic>Brucella</italic>, among which <italic>Brucella microti</italic>, but not in the “classical” species, with the exception of marine mammals strains. Recently, the glutaminase-dependent system (named AR2_Q), relying on the deamination of glutamine (Gln) into Glu and on GadC activity, was described in <italic>E. coli</italic>. In <italic>Brucella</italic> genomes, a putative glutaminase (<italic>glsA</italic>)-coding gene is located downstream of the <italic>gadBC</italic> genes. We found that in <italic>B. microti</italic> these genes are expressed as a polycistronic transcript. Moreover, using a panel of <italic>Brucella</italic> genus-representative strains, we show that the AR2_Q system protects from extreme acid stress (pH ≤2.5), in the sole presence of Gln, only the <italic>Brucella</italic> species/strains predicted to have functional <italic>glsA</italic> and <italic>gadC</italic>. Indeed, mutagenesis approaches confirmed the involvement of <italic>glsA</italic> and <italic>gadC</italic> of <italic>B. microti</italic> in AR2_Q and that the acid-sensitive phenotype of <italic>B. abortus</italic> can be ascribed to a Ser248Leu substitution in GlsA, leading to loss of glutaminase activity. Furthermore, we found that the gene BMI_II339, of unknown function and downstream of the <italic>gadBC–glsA</italic> operon, positively affects Gad- and GlsA-dependent AR. Thus, we identified novel determinants that allow newly discovered and marine mammals <italic>Brucella</italic> strains to be better adapted to face hostile acidic environments. As for significance, this work may contribute to the understanding of the host preferences of <italic>Brucella</italic> species and opens the way to alternative diagnostic targets in epidemiological surveillance of brucellosis.</p>