High ethanol tolerance of the thermophilic anaerobic ethanol producer Thermoanaerobacter BG1L1

Abstract

Abstract:The low ethanol tolerance of thermophilic anaerobic bacteria, generally less than 2% (v/v) ethanol, is one of the main limiting factors for their potential use for second generation fuel ethanol production. In this work, the tolerance of thermophilic anaerobic bacterium Thermoanaerobacter BG1L1 to exogenously added ethanol was studied in a continuous immobilized reactor system at a growth temperature of 70• C. Ethanol tolerance was evaluated based on inhibition of fermentative performance e.g. inhibition of substrate conversion. At the highest ethanol concentration tested (8.3% v/v), the strain was able to convert 42% of the xylose initially present, indicating that this ethanol concentration is not the upper limit tolerated by the strain. Long-term strain adaptation to high ethanol concentrations (6−8.3%) resulted in an improvement of xylose conversion by 25% at an ethanol concentration of 5% v/v, which is the concentration required in practice for economically efficient product recovery. For all ethanol concentrations tested, relatively high and stable ethanol yields (0.40 − 0.42 g/g) were seen. The strain demonstrated a remarkable ethanol tolerance, which is the second highest displayed by thermophilic anaerobic bacteria known to the authors. This appears to be the first study of the ethanol tolerance of these microorganisms in a continuous immobilized reactor system.

Metabolic engineering of a thermophilic bacterium to produce ethanol at high yield

“…The concentrations of ethanol produced by strain ALK2, 37 g/liter in fed batch culture and 33 g/liter in continuous culture, are higher than previously reported for thermophilic bacteria (13). These concentrations are, however, only approximately half the maximum concentration of added ethanol that will cease growth by ethanol-adapted thermophilic strains (23)(24)(25)(26)(27). Moreover, whereas ethanol can readily be recovered at the maximum concentrations tolerated by thermophiles, this is not the case for the maximum concentrations produced thus far.…”

Recent Advances in Second Generation Ethanol Production by Thermophilic Bacteria

“…Another Thermoanaerobacter strain has also been intensively investigated on the subject, Thermoanaerobacter BG1L1, an efficient xylose degrader. This bacterium showed 8.3% (v/v) tolerance in continuous culture studies [61]. Increased ethanol tolerance was also observed with Thermoanaerobacter thermohydrosulfuricus 39E by successively sub-culturing the strain to higher ethanol concentrations [79].…”

“…Another difference lies in the slightly higher Topt for Thermoanaerobacter species (mostly between 65 °C and 75 °C) as compared with Thermoanaerobacterium (mostly 55-65 °C). The type species, Thermoanerobacter ethanolicus and several other species within the genus have been extensively studied for ethanol production [52,[59][60][61][62][63][64][65][66][67] and the highest yields of ethanol production from sugar by a thermophile was observed by this species. Other high yielding species are T. pseudoethanolicus, T. mathranii, Thermoanaerobacter strain AK5 and Thermoanaerobacter strain J1 (Table 1).…”

Ethanol and Hydrogen Production with Thermophilic Bactera from Sugars and Complex Biomass

“…Several studies have been done with Clostridium thermosaccharolyticum (Baskaran et al, 1995;Klapatch et al, 1994) and Thermoanaerobacter sp. (Georgieva et al, 2008b) to increase EtOH tolerance. The highest EtOH tolerance is by a mutant strain of Thermoanaerobacter ethanolicus, or 9% (wt/vol) at 69°C (Carriera & Ljungdahl, 1983) but later studies with JW200 Fe(4), one of its derivatives, show much less tolerance (Hild et al, 2003).…”

“…The highest EtOH tolerance is by a mutant strain of Thermoanaerobacter ethanolicus, or 9% (wt/vol) at 69°C (Carriera & Ljungdahl, 1983) but later studies with JW200 Fe(4), one of its derivatives, show much less tolerance (Hild et al, 2003). Georgieva and co-workers published very high EtOH tolerance (8.3%) for Thermoanerobacter BG1L1, a highly efficient xylose degrader in continuous culture studies (Georgieva et al, 2008b). Thermoanerobacter thermohydrosulfuricus degrades various pentoses and hexoses as well as starch to high concentrations of EtOH (Ng et al, 1981).…”