Function of the SpoVAEa and SpoVAF Proteins of Bacillus subtilis

The Bacillus subtilis spoVAEa and spoVAF genes are expressed in developing spores as members of the spoVA operon, which en-codes proteins essential for the uptake and release of dipicolinic acid (DPA) during spore formation and germination. SpoVAF is likely an integral inner spore membrane protein and exhibits sequence identity to A subunits of the spore’s nutrient germinant receptors (GRs), while SpoVAEa is a soluble protein with no obvious signals to allow its passage across a membrane. However, like SpoVAD, SpoVAEa is present on the outer surface of the spore’s inner membrane, as SpoVAEa was accessible to an external biotinylation agent in spores and SpoVAEa disappeared in parallel with SpoVAD during proteinase K treatment of germinated spores. SpoVAEa and SpoVAD were also distributed similarly in fractions of disrupted dormant spores. Unlike spoVAD, spo-VAEa is absent from the genomes of some spore-forming members of the Bacillales and Clostridiales orders, although Spo-VAEa’s amino acid sequence is conserved in species containing spoVAEa. B. subtilis strains lacking SpoVAF or SpoVAEa and SpoVAF sporulated normally, and the spores had normal DPA levels. Spores lacking SpoVAF or SpoVAEa and SpoVAF also ger-minated normally with non-GR-dependent germinants but more slowly than wild-type spores with GR-dependent germinants, and this germination defect was complemented by ectopic expression of the missing proteins. The spoVA operon of Bacillus subtilis is expressed only in thedeveloping spore during sporulation and encodes seven pro-teins, with the genes in the order spoVAA,-B,-C,-D,-Eb,-Ea, and-F. At least five of these SpoVA proteins, SpoVAA,-B,-C,-D, and-Eb, are necessary for normal B. subtilis spore formation (1, 2). These proteins are essential for the uptake of dipicolinic aci