Abstract
Zymomonas mobilis, as an ethanologenic microorganism with many desirable industrial features, faces crucial obstacles in the lignocellulosic ethanol production process. A significant hindrance occurs during the pretreatment procedure that not only produces fermentable sugars but also releases severe toxic compounds. As diverse parts of regulation networks are involved in different aspects of complicated tolerance to inhibitors, we developed ZM4-hfq and ZM4-sigE strains, in which hfq and sigE genes were overexpressed, respectively. ZM4-hfq is a transcription regulator and ZM4-sigE is a transcription factor that are involved in multiple stress responses. In the present work, by overexpressing these two genes, we evaluated their impact on the Z. mobilis tolerance to furfural, acetic acid, and sugarcane bagasse hydrolysates. Both recombinant strains showed increased growth rates and ethanol production levels compared to the parental strain. Under a high concentration of furfural, the growth rate of ZM4-hfq was more inhibited compared to ZM4-sigE. More precisely, fermentation performance of ZM4-hfq revealed that the yield of ethanol production was less than that of ZM4-sigE, because more unused sugar had remained in the medium. In the case of acetic acid, ZM4-sigE was the superior strain and produced four and two-fold more ethanol compared to the parental strain and ZM4-hfq, respectively. Comparison of inhibitor tolerance between single and multiple toxic inhibitors in the fermentation of sugarcane bagasse hydrolysate by ZM4-sigE strain showed similar results. In addition, ethanol production performance was considerably higher in ZM4-sigE as well. Finally, the results of the qPCR analysis suggested that under both furfural and acetic acid treatment experiments, overproduction of both hfq and sigE improves the Z. mobilis tolerance and its ethanol production capability. Overall, our study showed the vital role of the regulatory elements to overcome the obstacles in lignocellulosic biomass-derived ethanol and provide a platform for further improvement by directed evolution or systems metabolic engineering tools.
Highlights
To decrease reliance on limited fossil reserves and to control global warming, an alternative environment-friendly fuel is important
As we can conclude from previous researches, this study aimed to consider the role of overproduction of hfq and sigE genes in response to acetic acid, furfural and sugarcane bagasse hydrolysate
The parental and recombinant strains of Z. mobilis were submitted to different concentrations of furfural and acetic acid treatments
Summary
To decrease reliance on limited fossil reserves and to control global warming, an alternative environment-friendly fuel is important. Bioethanol, as a sustainable energy source, can be a substitution for the finite resources of fossil fuels and is considered to decrease the rate of environmental pollution [1]. Various enzymes within the Embden–Meyerhof–Parnas (EMP) pathway, Krebs cycle and pentose phosphate pathway (PPP) are not identified in this microorganism. These truncated pathways and enzyme deficiencies drive more carbon flux into the ED pathway and bioethanol production [1, 2]. Fermentation by Z. mobilis does not need aeration control, and reduces the bioethanol production costs [2,3,4]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
