Genomic island 2 is an unstable genetic element contributing to Brucella lipopolysaccharide spontaneous smooth-to-rough dissociation.
Brucella is a Gram-negative bacterium that causes a worldwide-distributed zoonosis. The genus includes smooth (S) and rough (R) species that differ in the presence or absence, respectively, of the O-polysaccharide of lipopolysaccharide. In S brucellae, the O-polysaccharide is a critical diagnostic antigen and a virulence determinant. However, S brucellae spontaneously dissociate into R forms, a problem in antigen and S vaccine production. Spontaneous R mutants of Brucella abortus, Brucella melitensis, and Brucella suis carried the chromosomal scar corresponding to genomic island 2 (GI-2) excision, an event causing the loss of the wboA and wboB O-polysaccharide genes, and the predicted excised circular intermediate was identified in B. abortus, B. melitensis, and B. suis cultures. Moreover, disruption of a putative phage integrase gene in B. abortus GI-2 caused a reduction in O-polysaccharide loss rates under conditions promoting S-R dissociation. However, spontaneous R mutants not carrying the GI-2 scar were also detected. These results demonstrate that the phage integrase-related GI-2 excision is a cause of S-R brucella dissociation and that other undescribed mechanisms must also be involved. In the R Brucella species, previous works have shown that Brucella ovis but not Brucella canis lacks GI-2, and a chromosomal scar identical to those in R mutants was observed. These results suggest that the phage integrase-promoted GI-2 excision played a role in B. ovis speciation and are consistent with other evidence, suggesting that this species and B. canis have emerged as two independent lineages.
Mancilla
Marcos
M
Instituto de Bioquímica, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile.
López-Goñi
Ignacio
I
Moriyón
Ignacio
I
Zárraga
Ana María
AM
D001483:Base Sequence; D002002:Brucella / Q000145:classification / Q000166:cytology* / Q000235:genetics* / Q000378:metabolism; D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D044404:Genomic Islands / Q000235:genetics*; D008070:Lipopolysaccharides / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D013045:Species Specificity
D008070:Lipopolysaccharides