[Characterization of an acidotolerant, thermophilic Thermoanaerobacter sp. xyl-d with a high xylose conversion].

ABSTRACT

OBJECTIVE: We screened a thermophilic xylolytic bacterium that produced fuel ethanol from a high-temperature oil reservoir, and provided microbial resources to genetic engineering strains construction and consolidated bioprocessing. METHODS: We adopted Hungate anaerobic technique to isolate strain xyl-d from oil reservoir water sample enriched for two years from Shengli Oilfield in China, and we identified strain xyl-d with morphological, physiological, biochemical and phylogenetic analysis. RESULTS: Strain xyl-d was gram-negative, rod-shaped, spore-forming and strictly anaerobic. The growth temperature ranged from 30 degrees C to 85 degrees C (optimum 65 degrees C) and the pH ranged from 3.0 to 10.0 (optimum 7.5) and salt concentration was 0% - 4% (optimum at 2.0%). It converted D-xylose into ethanol, acetate, CO2, trace amount of iso-butanol and propionate. The genomic DNA G + C contents of strain xyl-d was 45.6 mol%. Based on 16S rRNA gene sequence, strain xyl-d was most close to Thermoanaerobacter wiegelii DSM10319(T) and Thermoanaerobacter ethanolicus DSM 2246(T) both with the 99.3% similarity. It produced more ethanol and less acetate at initial pH 8.5 than other pH. Ethanol yield was increased significantly with yeast extract, and ethanol became the main end product. In addition, growth of strain xyl-d was inhibited obviously with ethanol concentration more than 7% (V/V). In the optimum growth conditions, xylose degradation rates reached to 91.37%. CONCLUSION: Strain xyl-d was thermophilic, high xylose conversion rate, acidotolerant anaerobe. It was a potential bacterium that can be used for consolidated bioprocessing.