Enhancement of mono-acylated MEL-D production in an acyltransferase gene-deleted strain of by supplementation with di-acylated MEL-B in culture medium.

Mannosylerythritol lipids (MELs) are glycolipid biosurfactants produced by various yeasts. MEL producers produce mainly di-acylated MELs (consisting of two fatty acid chains). Among them, is a di-acylated MEL-B (d-MEL-B) producer. In a previous study, we generated an acyltransferase-deleted strain of . (Δ), which selectively produced mono-acylated MEL-D (m-MEL-D, consisting of one fatty acid chain), but not d-MEL-B. However, m-MEL-D productivity in Δ was low, and oil consumption was significantly reduced compared to the parent strain. Based on these findings, we hypothesized that the d-MEL-B produced by the parent strain may act as an emulsifier in the culture medium, leading to easier utilization of the oil. By contrast, the m-MEL-D produced by Δ may not have the ability to emulsify oil, thus the oil is used inefficiently and productivity of m-MEL-D is low. Therefore, we expected that adding d-MEL-B to the culture medium during Δ cultivation would increase m-MEL-D production. To enhance the oil consumption and m-MEL-D production of Δ, d-MEL-B and chemical surfactants were added to the culture medium as emulsifiers during Δ cultivation. Adding d-MEL-B enhanced both the oil consumption and m-MEL-D production of Δ; Tween 20 and Triton X-100 also showed enhancement effects. As expected, d-MEL-B, Tween20 and TritonX-100, showed marked olive oil emulsification activity, whereas m-MEL-D did not. These results strongly support our hypothesis and significantly improve m-MEL-D productivity.