In silico Simulation for Enhancing Production of Organic Acids in Zymomonas mobilis

Abstract

The anaerobic Zymomonas mobilis has been acknowledged as a promising microorganism for bioethanol production due to its numerous advantages over the popular bioethanol producer, Saccharomyces cerevisiae. Z. mobilis has higher sugar uptake, higher ethanol yield, and tolerance to higher ethanol concentration. Despite of many advantages of Z. mobilis, the wild strain ferments only glucose, fructose, and sucrose. Nevertheless, recent studies have successfully engineered strains, which were capable of fermenting xylose and arabinose. Several advanced studies were conducted to acquire more information regarding the physiology data that can be used to improve the production yield. These studies have so far been limited to time and resources consuming experimental work. Therefore, the use of biological model can enable a systematic approach for Z. mobilis strain improvement. To this end, we developed a complete model of Z. mobilis by reconstructing a genome- scale metabolic network. We built the stoichiometric model of Z. mobilis ATCC31821 (ZM4), based on its annotated genome and biochemical information. The reconstructed model successfully predicts the experimental observations of Z. mobilis ZM4 growht on glucose. The intracellular flux distribution obtained from the model analysis is in close agreement with NMR-measured fluxes in engineered strain fueled by various carbon sources (glucose, fructose and xylose). Further, comparative performance analysis with other ethanol producers (E. coli and S. cerevisiae) and gene essentiality analysis have also allowed us to confirm the functional role of pdc and adh genes in the ethanologenic activity of Z. mobilis, thus leading to better understanding of this natural ethanol producer.Subsequently, we explored the Z. mobilis metabolic capacity for organic acids production, particularly lactic acid, acetic acid, and succinic acid. We performed gene deletion analysis on central metabolic reactions and the results suggested that pyuvate is the key metabolite in Z. mobilis fermentation and knocking out the competing pyruvate- consuming reactions could lead to increased production of desired product. Thus, this finding could be used as assistance for conducting strain improvement to enhance organic acids production in Z. mobilis. © 2012 Elsevier B.V.