SILAC-based proteome analysis of Starmerella bombicola sophorolipid production

Starmerella (Candida) bombicola is the biosurfactant-producing species that caught the greatest deal of attention in the academic and industrial world due to its ability of producing large amounts of sophorolipids. Despite its high economic potential, the biochemistry behind the sophorolipid biosynthesis is still poorly understood. Here we present the first proteomic characterization of S. bombicola for which we created a lys1Δ mutant to allow the use of SILAC for quantitative analysis. To characterize the processes behind the production of these biosurfactants, we compared the proteome of sophorolipid producing (early stationary phase) and nonproducing cells (exponential phase). We report the simultaneous production of all known enzymes involved in sophorolipid biosynthesis including a predicted sophorolipid transporter. In addition, we identified the heme binding protein Dap1 as a possible regulator for Cyp52M1. Our results further indicate that ammonium and phosphate limitation are not the sole limiting factors inducing sophorolipid biosynthesis.