A strictly anaerobic, gram-positive, motile, sporulated bacterium, designated strain CIN5, was isolated from olive mill wastewaters after enrichment on cinnamic acid. The rod-shaped cells were slightly curved (0.4-1.1 x 2.0-15 microm) and occurred singly or in pairs. Strain CIN5 utilized a limited number of carbohydrates (glucose, fructose, maltose, sorbitol), grew optimally at 37 degrees C and at pH 7.3-7.5 and had a DNA G+C content of 29.1+/-0.3 mol%. Strain CIN5 was very closely related to Clostridium glycolicum DSM 1288T. Both strain CIN5 and the type strain of C. glycolicum transformed cinnamic acid to hydrocinnamic acid and a wide range of other cinnamic acid derivatives, including o-, m- and p-coumaric, o-, m- and p-methoxycinnamic, p-methylcinnamic, caffeic, ferulic and isoferulic acids, to their corresponding 3-phenylpropionic acids by reducing the double bond of the side chain. Glucose supplementation increased the rate of conversion markedly. The emendation of the description of C. glycolicum is proposed to include these new characteristics.