Organization of the Haemophilus ducreyi 35000 chromosome

A physical and rudimentary genetic map of the Haemophilus ducreyi strain 35000 genome was constructed. Pulsed-field gel electrophoresis was used to separate restriction fragments of H. ducreyi DNA digested with Sfil, I-Ceul, or Sfil plus I-Ceul. The sizes of the fragments were determined, and the circular chromosome was estimated to be 1757 kbp. The six I-Ceul fragments and four Sfil fragments were ordered into macrorestriction maps using Southern blot hybridization with random H. ducreyi clones as probes. It was shown that both H. ducreyi and the distantly related Haemophilus influenzae have six rrn operons marked by the locations of the I-Ceul sites. However, the two species displayed distinct I-Ceul restriction patterns. A second H. ducreyi strain, CIP542, displayed an identical I-Ceul pattern to that of H. ducreyi 35000, but Sfil digests of teh two strains were distinct. The orientation of the six rrn operons was determined and thirteen identified H. ducreyi genes positioned on the map of strain 35000.