(A) In wild-type cells, spoIIIC and spoIVCB are normally separated by the ~48 kb skin element that is excised by the SpoIVCA recombinase. This allows the transcription of a spoIIIC-spoIVCB gene fusion and synthesis of σK, which in association with GerE, regulates the expression of spore coat genes. In skinless cells, spoIVCB and spoIIIC are already fused, allowing synthesis of σK without chromosomal rearrangement.
(B) Fluorescence distributions of cells from either wild-type (black) or skinless (green) strains expressing PgerE-YFP at 5 hr after initiation of sporulation in re-suspension media. The right peak (fluorescence > 5 × 102) of the wild-type strain (black) has a mean intensity of 8 × 103, and the skinless strain (green) has a mean intensity of 3 × 103. The left green and black peaks (fluorescence < 5 × 102) likely represent non-PgerE-YFP-expressing cells since they are predominantly non-sporulating as determined by microscopy.
(C) Germination of wild-type or skinless spores on LB (black), mISP4 (green) or mISP4 + 10mM alanine (gray). For mISP4, CFU wild-type versus CFU skinless; p = 0.028 (unpaired t test, two-tailed).
(D) Germination of wild-type and ΔgerE (JDB3577) spores on LB (black), mISP4 (green), or ISP4+10 mM alanine (gray). For mISP4, CFU wild-type versus CFU ΔgerE; p = 0.005, unpaired t test, two tailed. Shown is the mean, and error bars represent the SD.