PRODUCTION OF CAPROIC ACID BY COCULTURES OF RUMINAL CELLULOLYTIC BACTERIA AND CLOSTRIDIUM-KLUYVERI GROWN ON CELLULOSE AND ETHANOL

Ruminal cellulolytic bacteria (Fibrobacter succinogenes S85 or Ruminoc occus flavefaciens FD-1) were combined with the non-ruminal bacterium Clostridium kluyveri and grown together on cellulose and ethanol. Succ inate and acetate produced by the cellulolytic organisms were converte d to butyrate and caproate only when the culture medium was supplement ed with ethanol. Ethanol (244 mM) and butyrate (30 mM at pH 6.8) did n ot inhibit cellulose digestion or product formation by S85 or FD-1; ho wever caproate (30 mM at pH 6.8) was moderately inhibitory to FD-1. Su ccinate consumption and caproate production were sensitive to culture pH, with more caproic acid being produced when the culture was control led at a pH near neutrality. In a representative experiment under cond itions of controlled pH (at 6.8) 6.0 g cellulose 1(-1) and 4.4 g ethan ol 1(-1) were converted to 2.6 g butyrate 1(-1) and 4.6 g caproate 1(- 1). The results suggest that bacteria that efficiently produce low lev els of ethanol and acetate or succinate from cellulose should be usefu l in cocultures for the production of caproic acid, a potentially usef ul industrial chemical and bio-fuel precursor.