Improvement of sophorolipids production from Starmerella riodocensis GT-SL1R strain under high carbon-to-nitrogen ratio

Sophorolipids (SLs), renowned glycolipid biosurfactants, are produced by non-pathogenic yeast Starmerella species, yielding high quantities. Their distinctive environmental compatibility and high biodegradable properties. In this study, we aimed to investigate the effect of the carbon-to-nitrogen (C/N) ratio on SLs production from Starmerella riodocensis GT-SL1R. Specifically, we explored how varying C/N ratios influence SLs production when using glucose and palm oil as carbon sources, and yeast extract as a nitrogen source, while also investigating genes and proteins related to SLs production. The results indicate that high C/N ratios maximize SLs production from this yeast species, with values of nearly 25 g/L. Genes related to SLs synthesis, encode putative enzymes including CP450 monooxygenase, glucose transferase I and II, acyl transferase, and lactone esterase, respectively, exhibited high expression levels when the yeast was cultured in media with high C/N ratios. However, when the yeast was cultured at a low C/N ratio or very high C/N ratio, these genes exhibited low expression levels. In conclusion, a high C/N ratio in the media can increase the production of SLs by the yeast S. riodocensis GT-SL1R and promote the expression of genes and proteins involved in SLs synthesis.