, Volume 45-46, Issue 1, pp 209-223

Organism development and characterization for ethanol production using thermophilic bacteria

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Abstract

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 (ΜI0)s was determined forClostridium thermosaccharolyticum grown on xylose at both 55 and 60 ‡C. (ΜI0)S exhibited an approximately linear pattern in relation to ethanol concentration. Based on least square linear fits to the data, ethanol concentrations corresponding to (Μ I0 S = 0.5 were 29 g/L ethanol at 60‡C, and 36 g/L ethanol at 55‡C, and 31 g/L for the data combined for both temperatures. It is concluded that ethanol inhibition is unlikely to constrain utilization ofC. thermosaccharolyticum in processes for ethanol production from cellulosic biomass. Growth at high substrate concentrations using a defined medium has been achieved forC. 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 ofC. thermocellum with the ultimate goal of pathway manipulation. Antibiotics effective againstC. thermocellum include chloramphenicol, thiamphenicol, and erythromycin at 125, 10, and 40 Μg/mL, respectively. Summarized is work describing a restriction system ofC. thermocellum and protection against it by methylation. Demonstration of restriction protection and antibiotic sensitivity provides two elements likely to be useful in the transformation ofC. thermocellum.