Production of long-chain hydroxy fatty acids by Starmerella bombicola.

To decrease our dependency for the diminishing source of fossils resources, bio-based alternatives are being explored for the synthesis of commodity and high-value molecules. One example in this ecological initiative is the microbial production of the biosurfactant sophorolipids by the yeast Starmerella bombicola. Sophorolipids are surface-active molecules mainly used as household and laundry detergents. Because S. bombicola is able to produce high titers of sophorolipids, the yeast is also used to increase the portfolio of lipophilic compounds through strain engineering. Here, the one-step microbial production of hydroxy fatty acids by S. bombicola was accomplished by the selective blockage of three catabolic pathways through metabolic engineering. Successful production of 17.39 g/l (ω-1) linked hydroxy fatty acids was obtained by the successive blockage of the sophorolipid biosynthesis, the ß-oxidation and the ω-oxidation pathways. Minor contamination of dicarboxylic acids and fatty aldehydes were successfully removed using flash chromatography. This way, S. bombicola was further expanded into a flexible production platform of economical relevant compounds in the chemical, food and cosmetic industries.

One-step production of unacetylated sophorolipids by an acetyltransferase negative Candida bombicola.

Sophorolipids from the non-pathogenic yeast Candida bombicola are applied commercially as biodegradable, eco-friendly surface active agents. These sophorolipids are produced by cultivation in presence of a hydrophobic carbon source and are always constituted of a mixture of structurally related molecules. For some applications however, certain structural variants perform better than others. Acetylation of the sophorolipid molecule is such a parameter that gains interest because of its influence on water solubility, foaming properties, and biological activity. Fully unacetylated sophorolipids therefore are interesting metabolites but cannot be produced in a pure way by conventional cultivation. Here we report the identification of the acetyltransferase gene AT, responsible for acetylation of de novo synthesized sophorolipids in Candida bombicola. By the creation of a Δat deletion mutant, we could create a yeast strain producing purely unacetylated sophorolipids with a yield of 5 ± 0.7 g/L using rapeseed oil as hydrophobic carbon source. In contrast to the chemical production of unacetylated sophorolipids used nowadays, the microbial production leads to mainly lactonic sophorolipids, in addition to minor amounts of acidic sophorolipids.

Cloning and functional characterization of the UDP-glucosyltransferase UgtB1 involved in sophorolipid production by Candida bombicola and creation of a glucolipid-producing yeast strain.

Sophorolipids produced by the non-pathogenic yeast Candida bombicola ATCC 22214 are glycolipid biosurfactants applied commercially as biodegradable and eco-friendly detergents. Their low cell toxicity, excellent wetting capability and antimicrobial activity attract the attention of high-value markets, such as the cosmetic and pharmaceutical industries. Although sophorolipid production yields have been increased by the optimization of fermentation parameters and feed sources, the biosynthetic pathway and genetic mechanism behind sophorolipid production still remains unclear. Here we identify a UDP-glucosyltransferase gene, UGTB1, with a key function in this economically important pathway. The protein shows sequence and structural homology to several bacterial glycosyltransferases involved in macrolide antibiotic synthesis. Deletion of UGTB1 in C. bombicola did not affect cell growth and resulted in a yeast producing glucolipids, thereby opening the route for in vivo production of these glycolipid intermediates. Activity assays on cell lysates confirmed that the identified gene is responsible for the second glucosylation step during sophorolipid production and illustrated that sophorolipid production in C. bombicola involves the stepwise action of two independent glucosyltransferases. The complete UGTB1 sequence data have been submitted to the GenBank database (http://www.ncbi.nlm.nih.gov) under Accession No. HM440974.