Abstract:
:A recently discovered thermophilic bacterium, Geobacillus thermoglucosidasius M10EXG, ferments a range of C5 (e.g., xylose) and C6 sugars (e.g., glucose) and is tolerant to high ethanol concentrations (10%, v/v). We have investigated the central metabolism of this bacterium using both in vitro enzyme assays and 13C-based flux analysis to provide insights into the physiological properties of this extremophile and explore its metabolism for bio-ethanol or other bioprocess applications. Our findings show that glucose metabolism in G. thermoglucosidasius M10EXG proceeds via glycolysis, the pentose phosphate pathway, and the TCA cycle; the Entner-Doudoroff pathway and transhydrogenase activity were not detected. Anaplerotic reactions (including the glyoxylate shunt, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase) were active, but fluxes through those pathways could not be accurately determined using amino acid labeling. When growth conditions were switched from aerobic to micro-aerobic conditions, fluxes (based on a normalized glucose uptake rate of 100 units (g DCW)(-1) h(-1)) through the TCA cycle and oxidative pentose phosphate pathway were reduced from 64 +/- 3 to 25 +/- 2 and from 30 +/- 2 to 19 +/- 2, respectively. The carbon flux under micro-aerobic growth was directed to ethanol, L-lactate (> 99% optical purity), acetate, and formate. Under fully anerobic conditions, G. thermoglucosidasius M10EXG used a mixed acid fermentation process and exhibited a maximum ethanol yield of 0.38 +/- 0.07 mol mol(-1) glucose. In silico flux balance modeling demonstrates that lactate and acetate production from G. thermoglucosidasius M10EXG reduces the maximum ethanol yield by approximately threefold, thus indicating that both pathways should be modified to maximize ethanol production.
journal_name
Biotechnol Bioengjournal_title
Biotechnology and bioengineeringauthors
Tang YJ,Sapra R,Joyner D,Hazen TC,Myers S,Reichmuth D,Blanch H,Keasling JDdoi
10.1002/bit.22181subject
Has Abstractpub_date
2009-04-01 00:00:00pages
1377-86issue
5eissn
0006-3592issn
1097-0290journal_volume
102pub_type
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