Abstract
Sophorolipids are one of the best known microbial biosurfactants and are produced by several yeast species. The best studied producer is Starmerella bombicola, a non-pathogenic yeast associated in nature with bumblebees. Sophorolipids are built up of the rare disaccharide sophorose, which is attached to a fatty acid through a glyosidic bound. Sophorolipids produced by S. bombicola mainly contain oleic acid as the incorporated hydrophobic group. Other chain lengths can, to a certain content, be incorporated by feeding the yeast with substrates of alternative chain lengths. However, the efficiency for such substrates is low as compared to the preferred C18 chain length and defined by the substrate specificity of the first enzymatic step in sophorolipid biosynthesis, i.e., the cytochrome P450 enzyme CYP52M1. To increase product uniformity and diversity at the same time, a new strain of S. bombicola was developed that produces sophorolipids with a palmitic acid acyl chain. This was achieved by heterologous expression of the cytochrome P450 cyp1 gene of Ustilago maydis and feeding with palmitic acid. Optimization of the production was done by protein and process engineering.
Highlights
Starmerella bombicola is a yeast known for its efficient production of sophorolipids, a kind of naturally produced glycolipid biosurfactants [1]
Engineering of S. bombicola by knocking-out the β-oxidation or enzymes involved in long-chain alcohol oxidation already improves the production of these novel new-to-nature molecules using cheaper substrates, but the traditional sophorolipids still remain a part of the mixture since de novo fatty-acid synthesis still occurs with subsequent incorporation of these fatty acids into the sophorolipids [9,10]
The native cyp52m1 gene of S. bombicola was replaced by the cyp1 gene of U. maydis in S. bombicola as described in the Materials and Methods section
Summary
Starmerella bombicola is a yeast known for its efficient production of sophorolipids, a kind of naturally produced glycolipid biosurfactants [1]. Engineering of S. bombicola by knocking-out the β-oxidation or enzymes involved in long-chain alcohol oxidation already improves the production of these novel new-to-nature molecules using cheaper substrates, but the traditional sophorolipids still remain a part of the mixture since de novo fatty-acid synthesis still occurs with subsequent incorporation of these fatty acids into the sophorolipids [9,10]. The major factors hindering a uniform and efficient production of new-to-nature molecules are de novo sophorolipid synthesis enzymes with quite strict substrate specificity, resulting in suboptimal production of these new types. Because the enzyme solely catalyzes terminal hydroxylation, issues associated with the stereochemistry of the hydroxy group are circumvented as well These features render CYP1 a promising candidate for creating sophorolipids with an altered fatty acid chain in S. bombicola
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