Expression of a P-type Ca2+-transport ATPase in Bacillus subtilis during sporulation

The open reading frame designated yloB in the genomic sequence of Bacillus subtilis encodes a putative protein that is most similar to the typically eukaryotic type IIA family of P-type ion-motive ATPases, including the endo(sarco)plasmic reticulum (SERCA) and PMR1 Ca2+-transporters, located respectively in the SERCA and the Golgi apparatus. The overall amino acid sequence is more similar to that of the Pmr1s than to the SERCAs, whereas the inverse is seen for the 10 amino acids that form the two Ca2+-binding sites in SERCA. Sporulating but not vegetative B. subtilis cells express the predicted protein, as shown by Western blotting and by the formation of a Ca2+-dependent phosphorylated intermediate. Half-maximal activation of phosphointermediate formation occurred at 2.5 muM Ca2+. Insertion mutation of the yloB gene did not affect the growth of vegetative cells, did not prevent the formation of viable spores, and did not significantly affect 45 Ca accumulation during sporulation. However, spores from knockouts were less resistant to heat and showed a slower rate of germination. It is concluded that the P-type Ca2+-transport ATPase from B. subtilis is not essential for survival, but assists in the formation of resistant spores. The evolutionary relationship of the transporter to the eukaryotic P-type Ca2+-transport ATPases is discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.