We traceda potential provenance of the commonly used BGstrains through an exhaustive search of the open literature and the archives of the University of Wisconsin,which suggested a possible lineage from which the ''military'' BGstrains were derived. The original source of the strains were the collections at the University of Wisconsin during the 1930s and 1940s, from which the strains were transferred to Camp Detrick at the initiation of the US Army's BW program at the beginning of the Second World War [6, 26] . At Camp Detrick, BG was used as a non-pathogenic surrogate in process development for sporeforming bacteria It is tempting to speculate that the University of Wisconsin supplied BG to Porton Down: A note found in the archive of Dr. Baldwin's papers, dated February 19, 1943 , contained an order from Dr. Fildes (presumably Sir Paul Fildes, a noted bacteriologist active in the British BW program at the time), for a batch of B. subtilis spores. It is not clear whether BG or B. subtilis subsp. subtilis was supplied, or whether this material was actually delivered. Unfortunately, original records describing in detail the maintenance of the strains during the period 1942-1955 were destroyed as per US Army policy at the time (Dr. Mark Wolcott, USAMRIID; personal communication), and the personnel who had first-hand knowledge of the strain passage histories and methods are deceased. Therefore, the actual source of the Camp Detrick isolates must be inferred from published work [6] , limited available documentation (e.g. ATCC 9372) and the genome sequences presented hereFrom Camp Detrick the isolates were eventually transferred to ATCC as B. subtilis var. niger ''red strain.'' The desire to maintain a phenotypically and genotypically uniform simulant throughout the biodefense communityprompted us to elucidate whether significant phenotypic and/or genomic differences had accumulated in any of the commonly used isolates during the growth and transfer of strains to different institutions and to compare the isolates in broad use today to the so-called ''Mil-Spec'' strain (ATCC 9372).In contrast, the origin of ATCC 49822 prior to acquisition F. Young's laboratory (the depositor) is unclear.