Fermentation of alanine and glycine by pure and syntrophic cultures ofClostridium sporogenes

Abstract

Clostridium sporogenes was grown on alanine, glycine and alanine + glycine in pure culture and in syntrophic cultures with methanogens. Batch and continuous pure cultures of C. sporogenes grew only poorly on alanine as the sole amino acid, due to an elevated hydrogen partial pressure and converted alanine to acetate, CO2, H2 and presumably NH3. Growth on glycine was also poor and accompanied by the formation of acetate, CO2, some H2 and NH3. In the presence of alanine + glycine C. sporogenes performed an almost stoichiometric Stickland reaction in batch cultures. However, some hydrogen accumulated and little more CO2 was produced than could be accounted for by alanine utilization. Excellent growth of C. sporogenes was observed in a chemostat culture on alanine and glycine. Both amino acids were quantitatively fermented, as judged from the acetate production. When alanine was the sole substrate in syntrophic cultures of C. sporogenes and Methanobacterium formicicum it was almost quantitatively utilized and methane was produced by interspecies hydrogen transfer. More methane was generated, when a H2/CO2− and acetate-utilizing Methanosarcina barkeri was co-cultured with C. sporogenes . Compared to pure cultures, glycine fermentation in syntrophic cultures of C. sporogenes and M. formicicum was not improved, but less of it was reductively converted to acetate, in favour of oxidative metabolism with the formation of CO2 and methane. More glycine was fermented in cocultures of C. sporogenes and Ms. barkeri . In syntrophic cultures growing in the presence of alanine and glycine not more glycine was utilized than in cultures growing in the presence of glycine alone. Judging from the acetate production, a reductive metabolism was predominant.