A Bacillus cereus Mutant Defective in Spore Coat Deposition

Abstract

Spores of B. cereus mutants selected for slow response to germinants and sensitivity to lysozyme were deficient in coat, but were heat-resistant and contained the same quantity of dipicolinic acid as the wild-type. While the average coat protein content of the spores was 25% of the wild-type, many spores were coatless with large whorls of coat deposited in the cytoplasm. These coat deposits were isolated in Renografin gradients and cross-reacted immunologically with wild-type coat. The proteins extractable from these deposits were virtually identical to those extracted from wild-type spores. The morphology of the coat deposits was very similar to coats of wild-type spores, but with a deficiency of the outermost cross-patched layer. The sites of formation and deposition were altered. Since the mutant reverted to a phenotype identical to the parental strain with a frequency consistent with an initial point mutation, apparently a single defect resulted in alteration of the deposition of the spore coats on to the outer forespore membrane. Despite this defect, mutant cells were able to synthesize and process spore coat precursors into an array of morphological layers very similar to the wild-type. There are apparently distinct morphogenetic pathways for the formation of the spore body and coat layers.