The taxonomic placement of B. atrophaeus has changed dramatically over the years. Originally isolated as B. globigii in 1900 (Migula) as a variant of B. subtilis, it was originally distinguished from B. subtilis by the formation of a black-tinted pigment on nutrient agar and by low rates of heterologous gene transfer from B. subtilis [11] . It has been alternately known as B. subtilis var. niger, B. niger, and has been confused with B. licheniformis [12] . Other than the formation of the dark pigment, it is virtually indistinguishable from B. subtilis by conventional phenotypic analysis [13] , and the lack of distinguishing metabolic or phenotypic features has contributed to the confusionin the taxonomic placement of this organism. Low interspecies DNA transfer frequencies suggested substantial divergence [11] . Based onanalysis of comparative DNA hybridization, phenotypicand biochemical tests, Nakamura advocated that pigment-producing B. subtilis-like isolates should be classified as a distinct species termed B. atrophaeus [13] . Recently, more sensitive typing methods such as amplified fragment length polymorphism analysis showed that B. atrophaeus strains could be classified into two major biovars: var. globigii encompassing the classical, commonly used BG isolates, and var. atrophaeus encompassing other closely related yet genetically distinct strains [14] .