The second step in the development of BG as a simulant appears to have been the deliberate selection of a hypersporulating variant [6, 47] . Importantly, the selection of a strain optimized for spore yield resulted in the fixation of a new spo0F allele that has no counterpart among the available spo0F sequences (Figure 8 ). The sole Spo0Fsequence that differs at position 101 is that of B. clausii, in which tyrosine replaces histidine. Notably, the spo0F(H101R) mutation is distinct from a separate spo0F(A98P) mutation present in the in vitro passaged 1013 isolates. Given that the amino acid sequence of B. atrophaeus Spo0F is identical to that of B. subtilis but for two conservative substitutions, it is likely to have very similar if not identical biochemical properties. Detrick-1 and 1942 likely represent one of the two R colony morphotypes described by Hayward et al. [6] , whereas the hypersporulating F morphotypes likely arose due to the emergence of the spo0F(H101R) mutation. However, the possibility that Detrick-1 represents a reversion mutant at this locus from Detrick-2 cannot formally be excluded, but since it represented the dominant morphotype in the 1952 Detrick vial we believe this is unlikely. The presence of the spo0F(H101R) allele in the ATCC 9372 strains suggests that these strains were acquired by ATCC after this mutation appeared within the Detrick lineage. Experiments to verify the roles of each allele in modulating sporulation are currently in progress. Preliminary results indicate that transformation of B. subtilis Dspo0F with B. atrophaeus DNA and selection of spo+ cells dramatically alters colony morphology independently of the spo0F allele introduced; additional studies to verify the effects of each allele are currently in progress (James Hoch, personal communication).