Identification of a new gene essential for germination of Bacillus subtilis spores with Ca²⁺-dipicolinate

Bacillus subtilis spores can germinate with a 1:1 chelate of Ca²⁺ and dipicolinic acid (DPA), a compound present at high levels in the spore core. Using a genetic screen to identify genes encoding proteins that are specifically involved in spore germination by Ca²⁺-DPA, three mutations were identified. One was in the gene encoding the cortex lytic enzyme, CwlJ, that was previously shown to be essential for spore germination by Ca²⁺-DPA. The other two were mapped to an open reading frame, ywdL, encoding a protein of unknown function. Analysis of ywdL expression showed that the gene is expressed during sporulation in the mother cell compartment of the sporulating cell and that its transcription is σ^E dependent. Functional characterization of YwdL demonstrated that it is a new spore coat protein that is essential for the presence of CwlJ in the spore coat. Assembly of YwdL itself into the spore coat is dependent on the coat morphogenetic proteins CotE and SpoIVA. However, other than lacking CwlJ, ywdL spores have no obvious defect in their spore coat. Because of the role for YwdL in a part of the spore germination process, we propose renaming ywdL as a spore germination gene, gerQ.