Engineering of Zymomons mobilis for Farnesene Production from Lignocellulosic Biomass Sugars

Zymomonas mobilis is a facultative anaerobe and is well known for both its high specific glucose uptake rate and rapid catabolism which results in remarkably specific ethanol productivity, exceeding by 3-5-fold that of yeast and 3-fold that of Escherichia coli.  Furthermore, Z. mobilis has been engineered to metabolize xylose, the second most abundant sugar in nature, to ethanol.   Interestingly, this microbe is found to contain the highest level of triterpenic isoprenoids (C30) within the bacterial kingdom.   This makes it an intriguing and promising candidate for production of compounds based on isoprenoid intermediates. Therefore, we explored the potential of redirecting intermediates from the native iosoprenoid pathway for farnesene synthesis.  By introducing farnesene synthase gene into the glucose and xylose co-utilizing strain of Z. mobilis 8b under a strong inducible promoter, we showed that the overexpression of heterologous farnesene synthase gene enabled the strain to convert the intermediate in the triterpenic isoprenoid synthesis pathway, into farnesene from both glucose and xylose as well as pretreated biomass hydrolysate.   To further improve the titer, we have begun to focus on strategies to improve the production by understanding and modulating the terpenoid and other metabolic pathways in Zymomonas. Several key genes are being studied for their effect on enhancing the carbon flux toward the hydrocarbon product.  We will report on the progress of the pathway engineering in a hydrocarbon-producing Z. mobilis strain and the impact of the engineering on the production of hydrocarbon compounds.