Introduction: Clostridium thermocellum is considered a model organism for consolidated bioprocessing, due to its ability to hydrolyze lignocellulosic biomass more efficiently than many other organisms and to produce ethanol.In order to meet the industrial requirements of ethanol yield and titer, metabolic engineering efforts have been made resulting in a strain that successfully displays increased ethanol yield with reduced amount of some byproducts.However, the ethanol yield in this engineered strain still does not meet the industrial requirements and significant amounts of amino acids are still produced. To attempt to decrease the level of amino acid excretion intended to improve the ethanol yield in C. thermocellum, it is essential to understand its metabolism and how it is affected by different cultivation conditions and mediumcompositions. This study aimed to gain an insight in how carbon- and nitrogenlimitation affect amino acid excretion in C. thermocellum, with the hypothesisthat excess of carbon and nitrogen yields more amino acid excretion. Methods: Mass-balance based calculations of rates and yields were used to analyze the metabolism of a wild-type of C. thermocellum (DSM 1313) grownanaerobically in carbon- or nitrogen-limiting chemostats. For this, Low-Carbonmedium containing, respectively, cellobiose (5 g/L) and urea (0.15 g/L) as the limiting nutrient was used. Both cultivations were performed at 55 °C, pH 7.0and 400 RPM shaking at a dilution rate of 0.1 h-1.Conclusions: Considering yields of total amino acids excreted in both limitations, it was hypothesized that C. thermocellum exploited the amino acid excretion to maintain carbon balance around the pyruvate node caused by excess of the carbon. Based on yield of valine excreted in particular, it was hypothesized that amino acid excretion was used to maintain redox balance in the metabolism of C. thermocellum, where malate shunt could play a major role.However, results of the Carbon-limitation did not allow any conclusion of nitrogen excess having an effect on amino acid excretion in C. thermocellum.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-246982 |
| Date | January 2019 |
| Creators | Phongsawat, Chonticha |
| Publisher | KTH, Skolan för kemi, bioteknologi och hälsa (CBH) |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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