Abstract
Zymomonas mobilis is the most efficient bacterial ethanol producer and its physiology is potentially applicable to industrial-scale bioethanol production. However, compared to other industrially important microorganisms, the Z. mobilis metabolome and adaptation to various nutritional and genetic perturbations have been poorly characterized. For rational metabolic engineering, it is essential to understand how central metabolism and intracellular redox balance are maintained in Z. mobilis under various conditions. In this study, we applied quantitative mass spectrometry-based metabolomics to explore how glucose-fed non-growing Z. mobilis Zm6 cells metabolically adapt to change of oxygen availability. Mutants partially impaired in ethanol synthesis (Zm6 adhB) or oxidative stress response (Zm6 cat) were also examined. Distinct patterns of adaptation of central metabolite pools due to the change in cultivation condition and between the mutants and Zm6 reference strain were observed. Decreased NADH/NAD ratio under aerobic incubation corresponded to higher concentrations of the phosphorylated glycolytic intermediates, in accordance with predictions of the kinetic model of Entner–Doudoroff pathway. The effects on the metabolite pools of aerobic to anaerobic transition were similar in the mutants, yet less pronounced. The present data on metabolic plasticity of non-growing Z. mobilis cells will facilitate the further metabolic engineering of the respective strains and their application as biocatalysts.
Highlights
Over recent decades, there has been an ever-growing interest in the production of renewable biofuels
This bacterium generates only 1 molecule of ATP per catabolizing 1 molecule of glucose, and it has been shown that its Tricarboxylic acid cycle (TCA) is truncated and Pentose phosphate pathway (PPP) is incomplete [5]
Another distinctive physiological characteristics of Z. mobilis is its high capacity of aerobic respiration, proceeding almost without concomitant energy production [3,6,7,8]
Summary
There has been an ever-growing interest in the production of renewable biofuels. Concerning the intracellular metabolome, these authors focussed on stationary phase cells with near-zero glucose concentration left in their growth media, and used GC-MS metabolite profiling with limited coverage of central metabolite pools Another recent work [12] monitored the metabolome of exponentially growing cultures during anaerobic to aerobic transition. 29191 (Zm6) and its mutant derivatives, catalase and alcohol dehydrogenase knock-out strains with altered aerobic physiology at metabolically active non-growing (resting) state under aerobic and anaerobic condition Such a comparative metabolomic analysis exposed the scale of catabolic plasticity of Z. mobilis without interfering with pathways related to cellular growth
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