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Title
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New substrates for mannosylerythritol lipid production by Moesziomyces aphidis
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Author
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Abstract
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| Mannosylerythritol lipids (MEL) receive increasing interest due to their high fermentation yield and excellent surface-active properties. Potential applications include use in pharmaceutical industry, cosmetics or bioremediation. However, industrialization of MEL is complicated due to the high cost of the production process. The use of vegetable oil as a substrate is one of the drivers for this production cost. Moreover, the use of agricultural land for biosurfactant production conflicts with the use of this land for food and feed. In this work, side and waste streams are proposed as a possible solution. A two-step fermentation was investigated (chapter 3), in which initially microbial oil is produced by Cutaneotrichosporon oleaginosus. This yeast is known for its ability to accumulate oil from various waste streams, such as volatile fatty acids through anaerobic digestion. Subsequently, the intracellular single cell oil was recovered by cell disruption using a ball mill. After cell lysis, the oleaginous cell lysate containing 12.1 g L-1 triacylglycerol as substrate was used for MEL production (chapter 4). A yield of 2.3 g MEL L-1 was obtained. After a gene expression study (chapter 5) to provide insight into the molecular basis of the observations, it was postulated that the presence of an unfavourable nitrogen source, NH4+, causes the deficiency of MEL accumulation. MEL production requires a high NADP+ flux, which is present when NO3- is used as a nitrogen source. However, this flux is obstructed by nitrogen catabolic repression in the presence of NH4+. Another interesting side stream is sludge from the dissolved air flotation (DAF) unit of a wastewater treatment plant. Lipid rich and biodegradable DAF sludge can be found in the food industry and offers potential as a substrate for MEL production. In this work, DAF sludge from the wastewater treatment plant of a sauce producer was demonstrated to be a potential substrate for MEL production with promising titers up to 9.7 g MEL L-1 (chapter 6). Currently, DAF sludge is often used for the production of biogas. A preliminary economic analysis shows potential for MEL produced from DAF sludge. However, the investment costs are high, there is a lot of variability in production, and there is limited application potential for MEL from DAF sludge. The use of different substrates affects not only the production cost of MEL, but also the MEL structure. Moesziomyces aphidis uses partial β-oxidation of lipid rich substrates for subsequent incorporation into MEL. Vegetable oil such as rapeseed oil as a substrate for MEL production results in limited structural variation, which in turn leads to limited applications. For certain applications, for example cleaning agents, more hydrophilic components are desirable. In this work, the use of fatty acid derivatives as substrates for new glycolipid structures with high application potential is described. Using ricinoleic acid, a hydroxylated fatty acid, as a substrate, MEL was successfully produced by M. aphidis (chapter 7). In addition to the typical MEL structures, a small and more hydrophilic fraction was obtained, which is not present when rapeseed oil or similar vegetable oil is used as a substrate. This more hydrophilic fraction ensured that no MEL droplets were formed in the medium, and no orange pigmentation was observed. The structure of this new component is not yet identified, but it is a MEL-like compound with molecular formula C30H54O13. This research contributes to the feasibility of industrial scale MEL production from waste streams, and an increased structural diversity of MEL-like compounds, resulting in an expanded range of potential applications. Future efforts should include the further elucidation of genetic regulation and expansion of the genetic toolbox for M. aphidis to increase MEL yields from waste and side streams. Furthermore, Identification of new-to-nature MEL-like surfactants should be followed by an application study. |
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Language
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English
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Publication
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Antwerp
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University of Antwerp, Faculty of Applied Engineering
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2023
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Volume/pages
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x, 129 p.
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Note
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:
Dries, Jan [Supervisor]
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Full text (publisher's version - intranet only)
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