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Biochemical and spectroscopic properties of Brucella microti glutamate decarboxylase, a key component of the glutamate-dependent acid resistance system.

ABSTRACT: In orally acquired bacteria, the ability to counteract extreme acid stress (pH ? 2.5) ensures survival during transit through the animal host stomach. In several neutralophilic bacteria, the glutamate-dependent acid resistance system (GDAR) is the most efficient molecular system in conferring protection from acid stress. In Escherichia coli its structural components are either of the two glutamate decarboxylase isoforms (GadA, GadB) and the antiporter, GadC, which imports glutamate and exports ?-aminobutyrate, the decarboxylation product. The system works by consuming protons intracellularly, as part of the decarboxylation reaction, and exporting positive charges via the antiporter. Herein, biochemical and spectroscopic properties of GadB from Brucella microti (BmGadB), a Brucella species which possesses GDAR, are described. B. microti belongs to a group of lately described and atypical brucellae that possess functional gadB and gadC genes, unlike the most well-known "classical" Brucella species, which include important human pathogens. BmGadB is hexameric at acidic pH. The pH-dependent spectroscopic properties and activity profile, combined with in silico sequence comparison with E. coli GadB (EcGadB), suggest that BmGadB has the necessary structural requirements for the binding of activating chloride ions at acidic pH and for the closure of its active site at neutral pH. On the contrary, cellular localization analysis, corroborated by sequence inspection, suggests that BmGadB does not undergo membrane recruitment at acidic pH, which was observed in EcGadB. The comparison of GadB from evolutionary distant microorganisms suggests that for this enzyme to be functional in GDAR some structural features must be preserved.

SUBMITTER: Grassini G

PROVIDER: S-EPMC4382515 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND: Using a combination of pyrosequencing and conventional Sanger sequencing, the complete genome sequence of the recently described novel Brucella species, Brucella microti, was determined. B. microti is a member of the genus Brucella within the Alphaproteobacteria, which consists of medically important highly pathogenic facultative intracellular bacteria. In contrast to all other Brucella species, B. microti is a fast growing and biochemically very active microorganism with a phenotype more similar to that of Ochrobactrum, a facultative human pathogen. The atypical phenotype of B. microti prompted us to look for genomic differences compared to other Brucella species and to look for similarities with Ochrobactrum. RESULTS: The genome is composed of two circular chromosomes of 2,117,050 and 1,220,319 base pairs. Unexpectedly, we found that the genome sequence of B. microti is almost identical to that of Brucella suis 1330 with an overall sequence identity of 99.84% in aligned regions. The most significant structural difference between the two genomes is a bacteriophage-related 11,742 base pairs insert only present in B. microti. However, this insert is unlikely to have any phenotypical consequence. Only four protein coding genes are shared between B. microti and Ochrobactrum anthropi but impaired in other sequenced Brucella. The most noticeable difference between B. microti and other Brucella species was found in the sequence of the 23S ribosomal RNA gene. This unusual variation could have pleiotropic effects and explain the fast growth of B. microti. CONCLUSION: Contrary to expectations from the phenotypic analysis, the genome sequence of B. microti is highly similar to that of known Brucella species, and is remotely related to the one of O. anthropi. How the few differences in gene content between B. microti and B. suis 1330 could result in vastly different phenotypes remains to be elucidated. This unexpected finding will complicate the task of identifying virulence determinants in the Brucella genus. The genome sequence of B. microti will serve as a model for differential expression analysis and complementation studies. Our results also raise some concerns about the importance given to phenotypical traits in the definition of bacterial species.

Project description:BackgroundBrucella microti was first isolated from common vole (Microtus arvalis) in the Czech Republic in Central Europe in 2007. As B. microti is the only Brucella species known to live in soil, its distribution, ecology, zoonotic potential, and genomic organization is of particular interest. The present paper is the first to report the isolation of B. microti from a wild boar (Sus scrofa), which is also the first isolation of this bacterial species in Hungary.ResultsThe B. microti isolate was cultured, after enrichment in Brucella-selective broth, from the submandibular lymph node of a female wild boar that was taken by hunters in Hungary near the Austrian border in September 2014. Histological and immunohistological examinations of the lymph node sections with B. abortus-, B. suis- and B. canis-specific sera gave negative results. The isolate did not require CO2 for growth, was oxidase, catalase, and urease positive, H2S negative, grew well in the presence of 20 μg/ml basic fuchsin and thionin, and had brownish pigmentation after three days of incubation. It gave strong positive agglutination with anti-A and anti-M but had a negative reaction with anti-R monospecific sera. The API 20 NE test identified it as Ochrobactrum anthropi with 99.9% identity, and it showed B. microti-specific banding pattern in the Bruce- and Suis-ladder multiplex PCR systems. Whole genome re-sequencing identified 30 SNPs in orthologous loci when compared to the B. microti reference genome available in GenBank, and the MLVA analysis yielded a unique profile.ConclusionsGiven that the female wild boar did not develop any clinical disease, we hypothesize that this host species only harboured the bacterium, serving as a possible reservoir capable of maintaining and spreading this pathogen. The infectious source could have been either a rodent, a carcass that had been eaten or infection occurred via the boar rooting in soil. The low number of discovered SNPs suggests an unexpectedly high level of genetic homogeneity in this Brucella species.

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Biochemical and spectroscopic properties of Brucella microti glutamate decarboxylase, a key component of the glutamate-dependent acid resistance system.

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