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Journal of Bacteriology, July 2006, p. 5003-5013, Vol. 188, No. 14
0021-9193/06/$08.00+0     doi:10.1128/JB.00086-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The Brucella abortus Cyclic ß-1,2-Glucan Virulence Factor Is Substituted with O-Ester-Linked Succinyl Residues

Mara S. Roset, Andrés E. Ciocchini, Rodolfo A. Ugalde, and Nora Iñón de Iannino*

Instituto de Investigaciones Biotecnológicas-Instituto Tecnológico de Chascomús (IIB-INTECH), Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional de General San Martín (CONICET-UNSAM), 1650 San Martín, Buenos Aires, Argentina

Received 17 January 2006/ Accepted 26 April 2006

Brucella periplasmic cyclic ß-1,2-glucan plays an important role during bacterium-host interaction. Nuclear magnetic resonance spectrometry analysis, thin-layer chromatography, and DEAE-Sephadex chromatography were used to characterize Brucella abortus cyclic glucan. In the present study, we report that a fraction of B. abortus cyclic ß-1,2-glucan is substituted with succinyl residues, which confer anionic character on the cyclic ß-1,2-glucan. The oligosaccharide backbone is substituted at C-6 positions with an average of two succinyl residues per glucan molecule. This O-ester-linked succinyl residue is the only substituent of Brucella cyclic glucan. A B. abortus open reading frame (BAB1_1718) homologous to Rhodobacter sphaeroides glucan succinyltransferase (OpgC) was identified as the gene encoding the enzyme responsible for cyclic glucan modification. This gene was named cgm for cyclic glucan modifier and is highly conserved in Brucella melitensis and Brucella suis. Nucleotide sequencing revealed that B. abortus cgm consists of a 1,182-bp open reading frame coding for a predicted membrane protein of 393 amino acid residues (42.7 kDa) 39% identical to Rhodobacter sphaeroides succinyltransferase. cgm null mutants in B. abortus strains 2308 and S19 produced neutral glucans without succinyl residues, confirming the identity of this protein as the cyclic-glucan succinyltransferase enzyme. In this study, we demonstrate that succinyl substituents of cyclic ß-1,2-glucan of B. abortus are necessary for hypo-osmotic adaptation. On the other hand, intracellular multiplication and mouse spleen colonization are not affected in cgm mutants, indicating that cyclic-ß-1,2-glucan succinylation is not required for virulence and suggesting that no low-osmotic stress conditions must be overcome during infection.

* Corresponding author. Mailing address: Instituto de Investigaciones Biotecnológicas, Av. Gral Paz 5445, CP1650, San Martín, Buenos Aires, Argentina. Phone: (5411) 4580 7255. Fax: (5411) 4752 9639. E-mail: norai{at}iib.unsam.edu.ar.

Journal of Bacteriology, July 2006, p. 5003-5013, Vol. 188, No. 14
0021-9193/06/$08.00+0     doi:10.1128/JB.00086-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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