Quantifying Growth and Maintenance Atp Requirements for Cofermentation of Glucose and Xylose by Metabolically Engineered Zymomonas Mobilis

摘要

An intracellular adenosine-5'-triphosphate (ATP) balance-based method is described for quantifying glucose- and xylose-associated growth and non-growth (maintenance) energy requirements. Zymomonas mobilis, a gram-negative bacterium that distinctively uses the Entner-Doudoroff pathway (net yield of only one mole ATP per mole of glucose or -putatively- xylose consumed), is capable of efficiently converting both glucose and xylose to ethanol as well as moderately tolerating acetic acid and other inhibitory components typically present in biomass hydrolyzates. We have measured the concentrations of sugars (glucose and xylose), ethanol, byproducts (e.g., xylitol and acetic acid), as well as intracellular ATP concentrations, across a 2-factor, 3-level response surface design using the methods of analysis, techniques, and calculations described previously [AIChE 2004 Annual Meeting Proceedings, paper 29a]. Batch and various continuous fermentations of mixtures of 5% glucose/5% xylose (w/v) were conducted at a temperature of 30 °C and at pH 5.0, 5.3, or 6.0 in the presence of varying amounts of acetic acid (0, 4, and 8 g/L) in the input fermentation media.