Spores of a Bacillus subtilis strain with a
gerD deletion mutation (Delta
gerD) responded much slower than wild-type spores to nutrient germinants, although they did ultimately germinate, outgrow, and form colonies. Spores lacking
GerD and nutrient germinant receptors also germinated slowly with nutrients, as did Delta
gerD spores in which nutrient receptors were overexpressed. The germination defect of Delta
gerD spores was not suppressed by many changes in the sporulation or germination conditions. Germination of Delta
gerD spores was also slower than that of wild-type spores with a pressure of 150 MPa, which triggers spore germination through nutrient receptors. Ectopic expression of
gerD suppressed the slow germination of Delta
gerD spores with nutrients, but overexpression of
GerD did not increase rates of spore germination. Loss of
GerD had no effect on spore germination induced by agents that do not act through nutrient receptors, including a 1:1 chelate of Ca2+ and
dipicolinic acid,
dodecylamine,
lysozyme in hypertonic medium, a pressure of 500 MPa, and spontaneous germination of spores that lack all nutrient receptors. Deletion of
GerD's putative
signal peptide or change of its likely diacylglycerylated
cysteine residue to
alanine reduced
GerD function. The latter findings suggest that
GerD is located in a spore membrane, most likely the inner membrane, where the nutrient receptors are located. All these data suggest that, while
GerD is not essential for nutrient germination, this
protein has an important role in spores' rapid response to nutrient germinants, by either direct interaction with nutrient receptors or some signal transduction essential for germination.