Abstract

This work showed ethanol production by a microbial consortium of Clostridium cellulolyticum and a recombinant Zymomonas mobilis (ZM4 pAA1). The ZM4 pAA1 and wild type ZM4 (ZM4 WT) were first tested on RM medium (ATCC 1341) containing 2% cellobiose as the carbon source. Ethanol production from ZM4 pAA1 was three times higher than that observed from the ZM4 WT. Concomitant with ethanol production was the reduction in OD from 2.00 to 1.580. The ZM4 pAA1 was then co-cultured with C. cellulolyticum using cellobiose and microcrystalline cellulose, respectively, as carbon sources. Results indicate that the ZM4 pAA1 with C. cellulolyticum utilized 2.0 g/L cellobiose, producing as much as 0.40 mM of ethanol, whereas only 0.20 mM ethanol was detected for the ZM4 WT co-cultured with C. cellulolyticum under similar conditions. A consortium of the ZM4 pAA1 and C. cellulolyticum using 7.5 g/L microcrystalline cellulose gave a far lower ethanol yield than when using cellobiose. In the latter case, ethanol production was detected within 5 days, whereas it took about 10 days for ethanol to be detectable for the ZM4 WT and C. cellulolyticum. Future efforts will concentrate on identifying suitable partners for the ZM4 pAA1, the correct concentration of feedstocks at which synergy will be observed, as well as optimize medium formulations and inoculation techniques.

Key words: Biofuel, ethanol, cellulosome, consortium, Zymomonas mobilis, Clostridium cellulolyticum.