The best-known acetone-butanol (solvent)-producing bacterium is the Weizmann organism, , which was used for starch-based industrial fermentation. In the past two decades, cultures of “C, ” from various culture collections have included organisms that were isolated for sugar (molusses)-based industrial solvent production. Recent biochemical and genetic studies have revealed significant differences among some of these “ strains. We used DNA-DNA reassociation to analyze 39 cultures of “ and phenotypically similar organisms from major collections. The results of this study clearly identified four groups with intergroup reassociation values of less than 30%. All of the intragroup values except the value for one strain were 68% or more, which supported species status for each group. The group (with ATCC 824 as the type strain) consisted of 17 cultures and had average reassociation values of 10% with the other three groups. All strains of produced riboflavin in milk, and the cultures were bright yellow, which is useful for differentiating this species from the other three uroups. The group (with VPI 5481 [= ATCC 25752] as the type strain) consisted of 16 cultures and included strains NCIMB 8052 and NCP 270. Strains NCP 262 and NRRL B643 constituted the third group, whereas strain N1–4 (“) and its derivative, strain N1-4081, formed the fourth group. At present, the last two groups are each represented by only one independent strain; difinitive descriptions of these two groups as two new or revived species will require further phenotypic characterization, as well as identification of additional strains. NCP 270, sp. strain NRRL B643, and “ were used in industrial solvent production from molasses, which confirms that the new organisms used for the sugar-based processes are distinct from .


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