Fermentation of isoleucine and arginine by pure and syntrophic cultures of Clostridium sporogenes

Abstract The fermentation of isoleucine, arginine and isoleucine + arginine by pure and syntrophic cultures of Clostridium sporogenes was investigated. Growth of C. sporogenes on isoleucine, if any, was poor, but some isoleucine was fermented to 2-methylbutyrate and hydrogen. In syntrophic cultures with Methanobacterium formicicum or Methanosarcina barkeri growth was better, and isoleucine was completely fermented, the hydrogen being used for methane production. Pure cultures of C. sporogenes grew on arginine and produced 5-aminovalerate, ornithine and acetate. The reducing equivalents for 5-aminovalerate production from intermediarily formed proline were provided by oxidative conversion of arginine to acetate and by oxidative metabolism of some amino acids present in the yeast extract. However, when isoleucine was available together with arginine in syntrophic cultures of C. sporogenes and M. formicicum , the reducing equivalents for arginine fermentation came mainly from the oxidation of isoleucine (Stickland reaction), and the hydrogen produced in excess served for the reduction of CO₂ to methane.