Journal of Bacteriology, September 1998, p. 4392-4400, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
(1-2) Glucan Synthetase Gene:
Genetic Complementation of Rhizobium meliloti ndvB and
Agrobacterium tumefaciens chvB Mutants
Instituto de Investigaciones
Biotecnológicas,
Received 25 February 1998/Accepted 25 June 1998
The animal pathogen Brucella abortus contains a gene,
cgs, that complemented a Rhizobium meliloti
nodule development (ndvB) mutant and an Agrobacterium
tumefaciens chromosomal virulence (chvB) mutant. The
complemented strains recovered the synthesis of cyclic
(1-2) glucan,
motility, virulence in A. tumefaciens, and nitrogen
fixation in R. meliloti; all traits were strictly associated with the presence of an active cyclic
(1-2) glucan synthetase protein in the membranes. Nucleotide sequencing revealed the
presence in B. abortus of an 8.49-kb open reading frame
coding for a predicted membrane protein of 2,831 amino acids (316.2 kDa) and with 51% identity to R. meliloti NdvB. Four
regions of the B. abortus protein spanning amino acids 520 to 800, 1025 to 1124, 1284 to 1526, and 2400 to 2660 displayed
similarities of higher than 80% with R. meliloti NdvB.
Tn3-HoHo1 mutagenesis showed that the C-terminal 825 amino
acids of the Brucella protein, although highly conserved in
Rhizobium, are not necessary for cyclic
(1-2) glucan
synthesis. Confirmation of the identity of this protein as B. abortus cyclic
(1-2) glucan synthetase was done by the construction of a B. abortus Tn3-HoHo1
insertion mutant that does not form cyclic
(1-2) glucan and lacks
the 316.2-kDa membrane protein. The recovery of this mutant from the
spleens of inoculated mice was decreased by 3 orders of magnitude
compared with that of the parental strain; this result suggests that
cyclic
(1-2) glucan may be a virulence factor in
Brucella infection.
*
Corresponding author. Mailing address: Instituto de
Investigaciones Biotecnológicas, Universidad Nacional de Gral
San Martín, Av. General Paz entre Av. Constituyentes y
Albarellos, San Martin 1650, Pcia de Buenos Aires, Argentina. Phone:
54-1-752-0021. Fax: 54-1-752-9639. E-mail:
rugalde{at}inti.gov.ar.
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