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.
Highlights
Zymomonas mobilis is a facultative anaerobic Gramnegative bacterium belonging to the alpha subdivision of the phylum Proteobacteria, class Alpha-Proteobacteria, orderSphingomonadales and familySphingomonadaceae
The present study aimed to study the effects of using a consortium of a recombinant Z. mobilis and C. cellulolyticum on the conversion of biomass to bioethanol and using this study as a Launchpad for further experimental studies and process improvement
The recombinant Z. mobilis bearing the plasmid vector pAA1 supported the findings of Yanase et al (2005) in which ZM4 re-engineered with β-glucosidase gene from Ruminococcus albus was able to secrete 61% through the cytoplasmic membrane which resulted in the production of 0.49 g ethanol per gram of cellobiose
Summary
Zymomonas mobilis is a facultative anaerobic Gramnegative bacterium belonging to the alpha subdivision of the phylum Proteobacteria, class Alpha-Proteobacteria, order. 1.0-2.0 × 4.0-5.0 μm, motile, does not sporulate, does not produce capsules, intracellular lipids or glycogen, optimal pH range for growth is 6 to 7.0, optimal temperature range is 25 to 31°C, the G + C content of the cellular DNA is about 47.5 to 49.5% with an average Tm of 89.3 to 89.5°C (Gunasekeran et al, 1990). Z. mobilis uses the Entner-Doudoroff (ED) pathway which is found in microrganisms that are strictly aerobic, conducts fermentation with 50% less ATP produced relative to the Embden-Meyerhof-Parnas (EMP) pathway, which leads to improved ethanol yield (Yang et al, 2016).
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