Spontaneous deletions and flanking regions of the chromosomally inherited hemolysin determinant of an Escherichia coli O6 strain

Abstract

The hemolytic E. coli strain 536 (O6) propagates spontaneous hemolysin-negative mutants at relatively high rates (10-3 to 10-4). One type of mutant (type I) lacks both secreted (external) and periplasmic (internal) hemolysin activity (Hly(ex)-/Hly(in)-) and in addition shows no mannose-resistant hemagglutination (Mrh-), whereas the other type (type II) is Hly(ex)-/Hly(in)+ and Mrh+. The genetic determinants for hemolysin production (hly) and for mannose-resistant hemagglutination (mrh) of this strain are located on the chromosome. Hybridization experiments with DNA probes specific for various parts of the hly determinant reveal that mutants of type I have lost the total hly determinant, whereas those of type II lack only part of the hlyB that is essential for transport of hemolysin across the outer membrane. Using a probe that contains the end sequence of the plasmid pHly152-encoded hly determinant (adjacent to hlyB), we determined that a related sequence flanks also the hlyB-distal end to the chromosomal hly determinant of E. coli 536. In addition several other similar or even identical sequences are found in the vicinity of the hlyC- and the hlyB-distal ends of both the chromosomal and the plasmid hly determinants.