Emended descriptions of Clostridium acetobutylicum and Clostridium beijerinckii, and descriptions of Clostridium saccharoperbutylacetonicum sp nov and Clostridium saccharobutylicum sp nov.

On the basis of 16S rRNA gene sequencing and DNA-DNA reassociation, industr ial solvent-producing clostridia have been assigned to four species. In thi s study, the phenotypic characteristics of Clostridium acetobutylicum, Clos tridium beijerinckii, 'Clostridium saccharoperbutylacetonicum', and an unna med Clostridium sp. represented by the strains NCP 262(T) and NRRL B643 are compared. In addition, a further 40 strains of solvent-producing clostridi a have been classified by biotyping, DNA fingerprinting and 16S rRNA gene s equencing. These included 14 C. beijerinckii strains, two strains currently designated as 'Clostridium kaneboi' and 'Clostridium butanologenum', and 2 4 production strains used in the commercial acetone-butanol fermentation. A ll of the C. beijerinckii strains were confirmed to have been classified co rrectly. The 'C. kaneboi' and 'C, butanologenum' strains require reclassifi cation as C: acetobutylicum and C. beijerinckii, respectively. The commerci al production strains were found to belong either to C. beijerinckii or to the unnamed Clostridium sp. For the comparative phenotypic studies of the f our species, representative strains were selected from each of the DNA-fing erprint subgroups within each species. These strains were analysed for thei r ability to utilize different carbohydrates, hydrolyse gelatin or aesculin , and produce indole, and were tested for the presence of catalase and urea se. On the basis of these results, several phenotypic traits were found to be useful for differentiating between the four species. The descriptions of C. acetobutylicum and C, beijerinckii have been emended. The names Clostri dium saccharoperbutylacetonicum sp. nov. [type strain =N1-4 (HMT) = ATCC 27 021(T)] and Clostridium saccharobutylicum sp. nov. (type strain = DSM 13864 (T) = ATCC BAA-117(T)) are proposed for the two new species.