Beschreibung:
<jats:title>Summary</jats:title><jats:p>In 1992 a new <jats:italic>Vibrio cholerae</jats:italic> strain, designated <jats:italic>V. cholerae</jats:italic> O139 Bengal, emerged which has been responsible for large outbreaks of cholera in India and Bangladesh. Previously, we have shown that this strain arose from a <jats:italic>V. cholerae</jats:italic> O1 strain by the acquisition of novel DNA. Sequence analysis revealed that the novel DNA is flanked by two genes, <jats:italic>rfaD</jats:italic> and <jats:italic>rfbQRS</jats:italic>, which are also found in O1 strains. The mosaic structure of rfaD<jats:sub>vco139</jats:sub> indicated that it was one of the regions involved in recombination between donor and acceptor DNA. However, sequence divergence between the O1 and O139 <jats:italic>rfbQRS</jats:italic> genes indicated that the second recombination site between donor and O1‐acceptor DNA is probably located downstream of <jats:italic>rfbD</jats:italic><jats:sub>vco139</jats:sub>. The DNA region between <jats:italic>rfaD</jats:italic><jats:sub>vco139</jats:sub> and <jats:italic>rfbQRS</jats:italic><jats:sub>vco139</jats:sub>, designated <jats:italic>otn</jats:italic>, contained seven open reading frames (ORFs). Two ORFs, <jats:italic>otnA</jats:italic> and <jats:italic>otnB</jats:italic>, showed homology with genes involved in cell‐wall polysaccharide synthesis. Mutations in <jats:italic>otnA</jats:italic> and <jats:italic>otnB</jats:italic> indicated that they are required for capsule synthesis but not lipopolysaccharide synthesis. The <jats:italic>otn</jats:italic> DNA is also found in<jats:italic>V. cholerae</jats:italic> O69 and O141 strains, and the organization of this DNA was essentially identical to that in the O139 strain. However, sequence divergence of the <jats:italic>otnAB</jats:italic> genes indicated that the O139 <jats:italic>otn</jats:italic> DNA region was not derived from the O69 or O141 strains. No antigenic relationship was found between the different <jats:italic>V. cholerae</jats:italic> serotypes carrying <jats:italic>otn</jats:italic> DNA, so the genes determining the antigenic specificity of the O antigen or capsule must be located outside the <jats:italic>otn</jats:italic> DNA. The O139 <jats:italic>otn</jats:italic> DNA contained a JUMPstart sequence, which is associated with polysaccharide‐synthetic genes in several bacterial species. Furthermore, a repeat motif was observed in extragenic regions. A number of observations suggest that these sequences may facilitate gene flow between <jats:italic>V. cholerae</jats:italic> strains and the assembly of clusters of functionally related genes.</jats:p>