SCREENING OF ANAEROBIC THERMOPHILIC BACTERIA

Screening of anaerobic thermophilic bacteria 43 ___________________________________________________________________________ 3 SCREENING OF ANAEROBIC THERMOPHILIC BACTERIA 3.1 Summary Fermentation of milk permeate to produce acetic acid under anaerobic thermophilic conditions (~ 60°C) was studied. Although none of the known thermophilic acetogenic bacteria can ferment lactose, it has been found that one strain can use galactose and two strains can use lactate. Moorella thermoautotrophica DSM 7417 and Moorella thermoacetica DSM 2955 were able to convert lactate to acetate at thermophilic temperatures with a yield of ~0.93 g/g. Among the strains screened for their abilities to produce acetate and lactate from lactose, Clostridium thermolacticum DSM 2910 was found to produce large amounts of lactate and acetate. However, it also produced significant amounts of ethanol, CO and H . 2 2The lactate yield was affected by cell growth. During the exponential phase, acetate, ethanol, CO and H were the main products of fermentation with an equimolar acetate/ethanol ratio, 2 2whereas during the stationary phase, only lactic acid was produced with a yield of 4 mol per mol lactose, thus reaching the maximal theoretical value. When this bacterium was co-cultured with M. thermoautotrophica, lactose was first converted mainly to lactic acid, then to acetic acid, with a zero residual lactic acid ...