The failure of different strains of Yersinia pestis to produce lipopolysaccharide O-antigen under different growth conditions is due to mutations in the O-antigen gene cluster

The lipopolysaccharide (LPS) from eight strains of Yersinia pestis which ha d been cultured at 28 degreesC appeared to be devoid of an O-antigen when a nalysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. LPS i solated from three of these strains which had been cultured at 37 degreesC also appeared to be devoid of an O-antigen. When the LPS from Y. pestis str ain CO92 was purified and analysed by matrix-assisted laser desorption-ioni sation time-of-flight mass spectrometry, the observed signals were in the m ass range predicted for molecules containing lipid A plus the core oligosac charide but lacking an O-antigen. The nucleotide sequence of Y. pestis stra in CO92 revealed the presence of a putative O-antigen gene cluster. However , frame-shift mutations in the ddhB, gmd, fcl and ushA genes are likely to prevent expression of the O-antigen thus explaining the loss of phenotype. (C) 2001 published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies.