A novel solvent-producing, anaerobic clostridium, strain P7(T), was isolated from sediment from an agricultural settling lagoon after enrichment with CO as the substrate. The metabolism of this Gram-positive, motile, spore-forming rod was primarily acetogenic. Acetate, ethanol, butyrate and butanol were the end-products of metabolism. Strain P7(T) grew on CO, H(2)/CO(2), glucose, galactose, fructose, xylose, mannose, cellobiose, trehalose, cellulose, starch, pectin, citrate, glycerol, ethanol, propanol, 2-propanol, butanol, glutamate, aspartate, alanine, histidine, asparagine, serine, betaine, choline and syringate as sole substrates. Growth was not supported by methanol, formate, D-arabinose, fucose, lactose, melibiose, amygdalin, gluconate, lactate, malate, arginine, glutamine or vanillate. Nitrate reduction, production of indole, gelatin hydrolysis and aesculin hydrolysis were not observed. Analysis of the 16S rRNA gene sequence of the isolate showed that it was closely related to Clostridium scatologenes ATCC 25775(T) (99.7% sequence similarity) and clostridial strain SL1(T) (99.8% sequence similarity). Strain SL1 had been classified as a strain of C. scatologenes. However, DNA-DNA reassociation analysis showed that both strain P7(T) and strain SL1 represented novel clostridial species. It is proposed that strain P7(T) (=ATCC BAA-624(T)=DSM 15243(T)) be classified as the type strain of Clostridium carboxidivorans sp. nov. and that strain SL1(T) (=ATCC BAA-623(T)=DSM 12750(T)) be reclassified as the type strain of Clostridium drakei sp. nov.