Sophorolipids from Torulopsis bombicola: possible relation to alkane uptake

Torulopsis bombicola produces extracellular sophorolipids when it is grown on water-insoluble alkanes. Sophorolipids and related model compounds, which were not themselves used for growth, were found to stimulate markedly the growth of T. bombicola on alkanes. This stimulatory effect was restricted to growth on C10 to C20 alkanes, whereas no significantly influence was observed for growth on fatty alcohols, fatty acids, glucose, or glycerol. The nonionic methyl ester of the glycolipid supported the greatest cell yield. However, a number of synthetic nonionic surfactants were unable to replace the glycolipid. When organisms were grown on hexadecane, stimulation of growth by sophorolipids was observed almost exclusively with strains of Torulopsis yeasts. In contrast, the growth of other typical alkane-utilizing yeasts, such as candida and Pichia strains, was inhibited or not affected. It appears that sophorolipids are involved in alkane dissimilation by T. bombicola through an undetermined mechanism.