Abstract
BackgroundThe twin problem of shortage in fossil fuel and increase in environmental pollution can be partly addressed by blending of ethanol with transport fuel. Increasing the ethanol production for this purpose without affecting the food security of the countries would require the use of cellulosic plant materials as substrate. Clostridium thermocellum is an anaerobic thermophilic bacterium with cellulolytic property and the ability to produce ethanol. But its application as biocatalyst for ethanol production is limited because pyruvate ferredoxin oxidoreductase, which diverts pyruvate to ethanol production pathway, has low affinity to the substrate. Therefore, the present study was undertaken to genetically modify C. thermocellum for enhancing its ethanol production capacity by transferring pyruvate carboxylase (pdc) and alcohol dehydrogenase (adh) genes of the homoethanol pathway from Zymomonas mobilis.ResultsThe pdc and adh genes from Z. mobilis were cloned in pNW33N, and transformed to Clostridium thermocellum DSM 1313 by electroporation to generate recombinant CTH-pdc, CTH-adh and CTH-pdc-adh strains that carried heterologous pdc, adh, and both genes, respectively. The plasmids were stably maintained in the recombinant strains. Though both pdc and adh were functional in C. thermocellum, the presence of adh severely limited the growth of the recombinant strains, irrespective of the presence or absence of the pdc gene. The recombinant CTH-pdc strain showed two-fold increase in pyruvate carboxylase activity and ethanol production when compared with the wild type strain.ConclusionsPyruvate decarboxylase gene of the homoethanol pathway from Z mobilis was functional in recombinant C. thermocellum strain and enhanced its ability to produced ethanol. Strain improvement and bioprocess optimizations may further increase the ethanol production from this recombinant strain.
Highlights
The twin problem of shortage in fossil fuel and increase in environmental pollution can be partly addressed by blending of ethanol with transport fuel
The present study explored the possibility of enhancing the ethanol production capacity of Clostridium thermocellum by transferring pyruvate decarboxylase and alcohol dehydrogenase genes from Zymomonas mobilis
C. thermocellum is a difficult species for plasmid transformation due to endospore formation and strict anaerobic growth [20]
Summary
The twin problem of shortage in fossil fuel and increase in environmental pollution can be partly addressed by blending of ethanol with transport fuel. Blending of ethanol with fossil fuel is recommended to address the problem of increasing demand for transportation fuel without environmental pollution. This implementation was planned because ethanol is derived from renewable biological sources, and has promising properties such as anti-knock potential [1, 2] and cleaner combustion [3, 4]. Several countries around the world are adopting this strategy, and are planning to increase the percentage of ethanol blending in a phased manner [5] In this context, allocation of natural resources for ethanol production in place of food production, and completing interests in ethanol for industrial and potable purposes are the major concerns to be addressed. Plant materials from forests, urban wastes, and agricultural wastes were considered for their utility as feedstock for ethanol production [10]
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