Ultrastructure and characterization of an asporogenic mutant of Clostridium botulinum type E

Abstract

The asporogenic mutant, RSpoIIIa, showed septum formation and a nearly completed forespore about 4 h after onset of sporulation. The cells show defects at a few sites of the forespore membrane, an absence of 'germ cell wall,' and within 8 h lysis of the cytoplasm occurred indicating that the mutant was blocked at stage III. Some aberrant envelopes were seen later. Lysis of the asporogenic mutant was inhibited for up to 36 h by the addition of 2.4% glucose or sucrose to the medium and 80% of the cells showed septum formation. A comparison of the phenotypic characteristics of the asporogenic RSpoIIIa and the sporogenic MSp⁺ mutants, as well as the wild type, showed the same ultrastructural changes during the development of the forespore with the accumulation of intracellular iodophilic granules. In addition, the mutants showed specific immunofluorescence and precipitin lines of identity with antisera against the wild-type strain, but unlike the toxigenic wild type, the mutants were nontoxigenic by mouse pathogenicity tests.