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Sophorolipids are biobased and biodegradable glycolipid surface-active agents contributing to the shift from petroleum to biobased surfactants, associated with clear environmental benefits. However, their production cost is currently too high to allow commercialisation. Therefore, a continuous sophorolipid production process was evaluated, i.e., a retentostat with an external filtration unit. Despite an initial increase in volumetric productivity, productivity eventually declined to almost 0gL-1 h-1. Following comprehensive metabolomics on supernatant obtained from a standardised retentostat, we hypothesised exhaustion of the N-starvation-induced autophagy as the main mechanism responsible for the decline in bolaform sophorolipid productivity. Thirty-six metabolites that correlate with RNA/protein autophagy and high sophorolipid productivity were putatively identified. In conclusion, our results unveil a plausible cause of this bola sophorolipid productivity decline in an industrially relevant bioreactor set-up, which may thus impact majorly on future yeast biosurfactant regulation studies and the finetuning of bola sophorolipid production processes.

Metabolites are substances that are formed within our bodies that help us live and grow. Examples include glucose and vitamin D. When changes happen in our bodies, like when we get sick, these metabolites can change. By studying metabolite changes, using a method called metabolomics, we can learn a lot about diseases, what causes them, and how to avoid them. We know that eating foods like fish, fruits, and vegetables is healthy. Eating too much red and processed meat, however, increases our chances of developing certain types of cancer. Unfortunately, we still do not understand why that is. It could be that there are unhealthy, toxic elements or substances in the meat itself or that there are toxic metabolites formed during or after the digestion of red and processed meat. To find out, we must journey into the gut, using metabolomics!