On the basis of 16S rRNA gene sequencing and DNA-DNA reassociation, industrial solvent-producing clostridia have been assigned to four species. In this study, the phenotypic characteristics of Clostridium acetobutylicum, Clostridium beijerinckii, 'Clostridium saccharoperbutylacetonicum', and an unnamed Clostridium sp. represented by the strains NCP 262T and NRRL B643 are compared. In addition, a further 40 strains of solvent-producing clostridia have been classified by biotyping, DNA fingerprinting and 16S rRNA gene sequencing. These included 14 C. beijerinckii strains, two strains currently designated as 'Clostridium kaneboi' and 'Clostridium butanologenum', and 24 production strains used in the commercial acetone-butanol fermentation. All of the C. beijerinckii strains were confirmed to have been classified correctly. The 'C. kaneboi' and 'C. butanologenum' strains require reclassification as C. acetobutylicum and C. beijerinckii, respectively. The commercial production strains were found to belong either to C. beijerinckii or to the unnamed Clostridium sp. For the comparative phenotypic studies of the four species, representative strains were selected from each of the DNA-fingerprint subgroups within each species. These strains were analysed for their ability to utilize different carbohydrates, hydrolyse gelatin or aesculin, and produce indole, and were tested for the presence of catalase and urease. 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 Clostridium saccharoperbutylacetonicum sp. nov. [type strain = N1-4 (HMT) = ATCC 27021T] and Clostridium saccharobutylicum sp. nov. (type strain = DSM 13864T = ATCC BAA-117T) are proposed for the two new species.

Ng, Henry (University of California, Davis) and Reese H. Vaughn. Clostridium rubrum sp. n. and other pectinolytic clostridia from soil. J. Bacteriol. 85:1104-1113. 1963.-Reports in the literature and results of experiments described herein suggest that pectinolytic anaerobes constitute a very heterogeneous group. The cultures isolated in this study all belonged to the genus Clostridium. The following species were identified: C. butyricum, C. fallax, C. multifermentans, and C. indolis. In addition, a species believed to be previously undescribed was named C. rubrum sp. n. The ability to ferment galacturonic acid was found to be adaptive. Some cultures fermented pectin and pectic acid to the same degree, whereas others fermented pectin only partially. The partial fermentation was attributed to the lack of a pectinesterase. On the basis of fermentation balances, it was concluded that the four strains of galacturonic acid fermenters selected for study yielded identical end products in approximately the same proportions. Per mole of galacturonic acid fermented, about 2 moles of CO(2), 1.5 moles of H(2), 1.5 moles of acetic acid, and 0.25 mole of butyric acid were produced.