3). Identification and characterization of several structural proteins of both the inner basal layer(s) and the external DNA Damage inhibitor projections of the exosporium has in recent years increased our knowledge on this poorly understood component of the bacterial spore (Charlton et al., 1999; Sylvestre et al., 2002; Steichen et al., 2003; Todd et al., 2003; Redmond et al., 2004; Fazzini et al., 2010; Terry et al., 2011; Thompson et al., 2011a, b). The current study identified BC1245 as a spore-specific protein. Bc1245 is highly conserved in members of the B. cereus group (B. anthracis, B. cereus, B. thuringiensis and B. weihenstephanensis)

supportive of an important function of the gene (and possibly its gene product) in this group of bacteria. Members of the B. cereus

group are known to have an exosporium as the outermost part of their spores, and as bc1245 was present in this group of bacteria while other Bacilli species such as B. subtilis lack the gene, we wanted to investigate whether bc1245 encode an exosporium protein. In silico analysis find more indicated that the bc1245 promotor was under control of the mother cell–specific sigma factor K (σK), which regulon in B. subtilis includes a series of genes encoding outer spore structural components such as coat proteins (Errington, 1993; Haldenwang, 1995). Real-time PCR revealed that bc1245 is transcribed late in sporulation (at the onset of phase-bright spores) and expressed at the same time as high expression of sigG and sigK. Although expression is declining, sigE and sigF are also expressed in the time frame of bc1245 expression. Further studies on expression of bc1245 in sigma factor-mutant strains and determination of the transcription start will determine the sigma factor-regulating expression of bc1245. The combination, however, of the prediction of a sigma factor K-dependent promotor and simultaneous expression with sigK make it plausible that bc1245

might encode a structural outer spore protein in the σK regulon. A recent study describing a novel exosporium protein BetA used the finding of putative σK-directed promotor elements as a search criterium when looking for filipin genes encoding exosporium proteins in B. anthracis (Thompson et al., 2011a, b). Also exosporium proteins BclA and BxpA are preceded by a consensus sequence for a promotor recognized by σK (Sylvestre et al., 2002; Steichen et al., 2003). Unfortunately, we do not yet know the function of BC1245 as a bcΔ1245 mutant was unaltered in spore heat resistance, hydrophobicity, germination and outgrowth capacity when compared with wild-type B. cereus. Further characterization of the mutant spore would be valuable, for example, visualization of the outer spore surface by different microscopic techniques such as electron cryomicroscopy or atomic force microscopy as described by Kailas et al. (2011).