Starmerella bombicola sophorolipid MDR transporter: from fundamental studies to improved production of novel biosurfactants

Surfactants are amphiphilic molecules, defined as surface active agents. They are used for a wide variety of applications in households, industry, and agriculture, thus belonging to chemicals of high economic importance. However, concerning the increasing environmental awareness, natural microbial-derived surfactants (biosurfactants) have gained increasing interest since they are produced from renewable-resource substrates, and demonstrate high biodegradability and low eco-toxicity. The organism of choice for the production of biosurfactants is the yeast Starmerella bombicola, capable of producing over 400g/L of sophorolipids. Although the sophorolipids have already been commercialized, the well-defined biosurfactant molecular structures determined by the producing organism limit their economic potential. Since the increasing industrial demand for biologically derived surfactants of extended structural diversity, S. bombicola has been transformed into a platform for the production of tailor-made glycolipids. Indeed, this yeast has been used for the efficient production of various glycolipids, such as pure lactonic, pure acidic and bola-form SLs. Other molecules including cellobiose lipids, glucolipids and non-acetylated sophorolipids, were synthesised in significantly lower amounts due to limited transport over the cellular membrane to the extracellular space. To resolve mentioned difficulties associated with the secretion of some structurally different glycolipids, transport mechanisms and preferences of the SL transporter need to be understood. The S. bombicola SL transporter is a multidrug resistance protein (MDR) of the ATP-binding cassette (ABC) superfamily. The role of these ATP binding permeases is to carry out the transport of some compounds and ions including salt ions, sugars, lipids, toxins, and secondary metabolites. Detailed characterisation and evaluation of SL MDR transporter specificity will be performed by heterologous expression in Saccharomyces cerevisie and subsequent analysis using vesicular transport assays. In order to get acquainted with these procedures the candidate will get training at Rega Institute- Department of Microbiology and Immunology, KU Leuven under supervision of Prof. Dr. Tassos Economou. Protein engineering will provide insight and useful knowledge on the structure-function relation of the protein and pin-point regions responsible for activity and substrate recognition. This way it will be applied to create transporters with improved selectivity towards difficult to secrete glycolipids. Simultaneously, in order to create strains with wider production potentials, the candidate will perform screening of the glycolipids transporters of other organisms, and heterogeneously express the ones which show the desired substrate specificity in particular S. bombicola strains. The newly created mutants with improved properties will be evaluated and compared to the maternal strains..