Strains and growth conditions B. atrophaeus strains and their sources are indicated in Table 1 . Archival strains were maintained as spores in sterile soil at the University of Wisconsin (Figure 1 ). The 1013 lineage, originally founded from the 1942 strain, was extensively passaged by serial transfer every 12-18 months on agar slants for 30 years. Unless otherwise indicated, strains were grown using LB agar plates, LB agar brothor Tryptic Soy agar containing 5% sheep's blood (SBA, HealthLink) at 37uC.