We obtained isolates from archival spore suspensions in sterile soilfrom the University of Wisconsin with legible labels dating back as far as 1942 ( Figure 1 ; Table 1 ). These isolates included an archival stock dated 1942 that likely predated the transfer to Camp Detrick, as well as material that had been returned to the University of Wisconsin from Camp Detrick in 1952. A derivative of the 1942 strain that had been repeatedly passaged in vitro on agar slants over a period ofapproximately 30 years allowed us to compare the genomic signatures of deliberate selection with the effects of long-term in vitro passage. In addition, a sample of strain NRS-356 [13] , which is mentioned as a possible parent strain in correspondence between various academic laboratories and Camp Detrick, was also obtained from the same source as the 1942 ''Vogel'' strain. These isolates were subsampled, germinated on LB plates, screened for colony morphology variation (see below). Genomic DNA was prepared from these isolates for sequencing.