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Infect. Immun., 05 1995, 1674-1680, Vol 63, No. 5
T Dasgupta and JS Lam
Previous work from this laboratory has shown that a 26-kb insert in cosmid
clone pFV100, isolated from a Pseudomonas aeruginosa gene library,
contained genes that could restore serotype-specific B-band
lipopolysaccharide (LPS) expression in rough mutant ge6. In this study,
subclones from pFV100 were made to identify genes responsible for B- band
LPS synthesis. Transformation of Escherichia coli HB101 with cosmid clone
pFV100 resulted in expression of P. aeruginosa serotype O5 B-band LPS,
indicating the presence of an rfb cluster in pFV100. Expression of P.
aeruginosa LPS could not be achieved in E. coli HB101 transformed with any
of the subclones. Complementation studies of well- characterized rough
mutants of P. aeruginosa PAO1 deficient in B-band LPS biosynthesis were
performed with the various subclones. Subclone pFV110, containing a 1.4-kb
XbaI-HindIII insert, restored B-band LPS biosynthesis in mutant AK44 (A+B-;
complete core). Probing chromosomal DNA from the 20 International Antigenic
Typing Scheme serotypes with the 1.4-kb insert from pFV110 in Southern
hybridizations revealed a positive reaction to restriction fragments in
serotypes O2, O5, O16, O20, and O18. LPS of serotypes O2, O5, O16, and O20
were shown earlier to have a similar backbone structure in their O antigen.
The insert in pFV110 was sequenced, and the deduced amino acid sequence was
compared with sequences of protein databases. No significant homology could
be detected with any sequences in the database. Open reading frame analysis
identified one region, ORF303, which could encode a 33-kDa protein. Using
E. coli maxicells for protein expression, orf303 mediated the expression of
a unique polypeptide with an apparent molecular mass of 32.5 kDa. The
deficiency in the synthesis of B-band LPS biosynthesis in mutant AK44 is
apparently complemented by the 33- kDa protein encoded by orf303. We have
designated this ORF rfbA. This investigation is the first report on cloning
and sequencing of an rfb gene involved specifically in O-antigen
biosynthesis in P. aeruginosa PAO1.
Copyright © 1995, American Society for Microbiology
Identification of rfbA, involved in B-band lipopolysaccharide biosynthesis in Pseudomonas aeruginosa serotype O5
Canadian Bacterial Diseases Network, University of Guelph, Ontario, Canada.
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