ORGANISM DEVELOPMENT AND CHARACTERIZATION FOR ETHANOL-PRODUCTION USING THERMOPHILIC BACTERIA

This article provides an overview and evaluation of our recent interdi sciplinary work having a bearing on ethanol production using thermophi lic bacteria. Based on steady-state effluent substrate concentrations in continuous culture, the ratio of the ethanol-inhibited growth rate and the uninhibited growth rate ((mu I)/(mu O))(S) was determined for Clostridium thermosaccharolyticum grown on xylose at both 55 and 60 de grees C. ((mu I)/(mu O))(S) exhibited an approximately linear pattern in relation to ethanol concentration. Based on least square linear fit s to the data, ethanol concentrations corresponding to ((mu I)/(mu O)) (S) = 0.5 were 29 g/L ethanol at 60 degrees C, and 36 g/L ethanol at 5 5 degrees C, and 31 g/L for the data combined for both temperatures. I t is concluded that ethanol inhibition is unlikely to constrain utiliz ation of C. themrosaccharalyticum in processes for ethanol production from cellulosic biomass. Growth at high substrate concentrations using a defined medium has been achieved for C. thermocellum in continuous culture with essentially complete substrate utilization at 54 g/L cell obiose concentration. We also include work aimed at elucidating the mo lecular genetics of C. thermocellum with the ultimate goal of pathway manipulation. Antibiotics effective against C. thermocellum include ch loramphenicol, thiamphenicol, and erythromycin at 125, 10, and 40 mu g /mL, respectively. Summarized is work describing a restriction system of C. thermocellum and protection against it by methylation. Demonstra tion of restriction protection and antibiotic sensitivity provides two elements likely to be useful in the transformation of C. thermocellum .