This article provides an overview and evaluation of our recent interdisciplinary work having a bearing on ethanol production using thermophilic 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 degrees C. ((mu I)/(mu O))(S) exhibited an approximately linear pattern in relation to ethanol concentration. Based on least square linear fits 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 55 degrees C, and 31 g/L for the data combined for both temperatures. It is concluded that ethanol inhibition is unlikely to constrain utilization 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 cellobiose concentration. We also include work aimed at elucidating the molecular genetics of C. thermocellum with the ultimate goal of pathway manipulation. Antibiotics effective against C. thermocellum include chloramphenicol, 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. Demonstration of restriction protection and antibiotic sensitivity provides two elements likely to be useful in the transformation of C. thermocellum.