Sunday, April 29, 2007 - 2:20 PM

Conversion of sugars in undetoxified lignocellulosic hydrolysates using thermophilic bacteria

Tania I. Georgieva, BioCentrum-DTU, Technical University of Denmark, Building 227, DK-2800 Lyngby, Denmark and Birgitte K. Ahring, Bsel, WSU, 2710 University Drive, Richland, WA 99354, Denmark.

Some gram-positive thermophilic anaerobic bacteria have unique ability to metabolise naturally both pentose and hexose sugars into ethanol. Moreover, there are a number of potential advantages associated with the production of ethanol at higher temperatures, including high bioconversion rates, low risk of contamination, and facilitate product recovery. This group of organisms has, however, not been seriously considered for ethanol fermentation since at present, there is only limited data for using these organisms under conditions of practical interest including high substrate concentrations and real hydrolysate media.

 Recently, we succeeded in developing a lactate dehydrogenase deficient mutant of bacterial strain Thermoanaerobacter BG1 (e.g. BG1L1). Results of an extended study of continuous thermophilic ethanol fermentation at 70°C in a lab-scale fluidized bed reactor using the mutant strain Thermoanaerobacter BG1L1 will be presented. The strain was able to co-ferment effectively glucose and xylose with an ethanol yield up to 0.45 g/g and an ethanol productivity of 1 g/l/h. In the presentation special attention will be given to the fermentation of undetoxified lignocellulosic hydrolysates such as wheat straw and corn stover hydrolysates. Data of strain tolerance to ethanol will also be presented and discussed in the context of using thermophilic continuous fermentation with high cell density in real production scale.

 Overall, the results obtained in our studies reveal a bright future for using specialized thermophilic anaerobic bacteria as ethanol producers during conversion of lignocellulosic biomasses.