From lab to market: An integrated bioprocess design approach for new-to-nature biosurfactants produced by Starmerella bombicola

Abstract : Glycolipid microbial biosurfactants, like sophorolipids (SLs), generate high industrial interest as 100% biobased alternatives for traditional surfactants. A well-known success story is the efficient SL producer Starmerella bombicola, which reaches titers well above 200 g/L. Recent engineering attempts have enabled the production of completely new types of molecules by S. bombicola, like the ‘non-symmetrical bolaform (nsBola) SLs’. As classic SLs are mostly applied in eco-friendly detergents, the possible use of these bolaform SLs in detergent applications was evaluated by scaling up the production process (150 L) and evaluating the purified product. This paper shows that they can be used as green and non-irritant surfactants in for example (automatic) dishwasher applications. However, the limited chemical stability at higher pH values (> 6.5), due to the presence of an ester function in the biosurfactant molecule, is a major drawback that will most likely inhibit market introduction. An integrated bioprocess design was thus applied to resolve this issue. The strategy was to replace the fed fatty acids, responsible for the ester bond in nsBola SLs, with fatty alcohols, to generate so-called ‘symmetrical bolaform (sBola) SLs’, containing two instead of one glycosidic bond. This requires a change in the feeding strategy, but also the blocking the fatty alcohols from metabolizing/oxidizing through the suggested ω-oxidation pathway. Two putative fatty alcohol oxidase genes (fao1 and fao2) were identified in the S. bombicola genome and deleted in the nsBola SL producing strain (ΔatΔsble). Shake flask experiments for these new strains (ΔatΔsbleΔfoa1 and ΔatΔsbleΔfoa2) were performed to evaluate if the fed fatty alcohols were directly implemented into the SL biosynthesis pathway. Indeed, sBola SL production up to 20 g/L was observed for the ΔatΔsbleΔfao1 strain, while the ΔatΔsbleΔfao2 strain only produced nsBola SLs. The sBola SLs were purified and their symmetrical structure was confirmed by NMR. They were found to be significantly more stable at higher pH, opening up the application potential of the biosurfactant by enhancing its stability properties.
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Lisa Renterghem, Sophie Roelants, Niki Baccile, Katrijn Uyttersprot, Marie Taelman, et al.. From lab to market: An integrated bioprocess design approach for new-to-nature biosurfactants produced by Starmerella bombicola. Biotechnology and Bioengineering, Wiley, In press, 115 (5), pp.1195-1206. ⟨10.1002/bit.26539⟩. ⟨hal-01685428⟩

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