The non-pathogenic yeast Starmerella bombicola CGMCC 1576 is an efficient producer of sophorolipids (SLs). The lactonic SLs are mainly produced with yeast extract, and the acidic SLs are mainly produced with ammonium sulfate. Naturally produced SLs are a mixture of various lactonic and acidic SLs. Usually, the SL mixture is not well separated technically, and the separation cost is relatively high. In order to reduce the cost of separation, four secreted aspartic protease-like proteins were identified through proteomic analysis of fermentation broth of S. bombicola under different nitrogen source conditions. The coding genes of the four proteins, namely, sapl1, sapl2, sapl3, and sapl4, are of high sequence similarity (above 55%) and included in a gene cluster. The expression of the four genes was significantly upregulated on (NH₄)₂SO₄ compared with that on yeast extract. The four genes were deleted together to generate a strain Δsapl. The titer of SLs in Δsapl reached 60.71 g/L after 5 days of fermentation using (NH₄)₂SO₄ as the nitrogen source and increased by 90% compared with the wild-type strain. The concentration of acidic SLs was 55.84 g/L, accounting for 92% of the total SLs. The yield of SLs from glucose (g/g) by Δsapl was 0.78, much higher than that by wild-type strain (0.47). However, no increase of SLs production was observed in Δsapl under yeast extract condition. Compared with that of the wild-type strain, the expression levels of the key genes for SLs synthesis were all upregulated to varying degrees in Δsapl under (NH₄)₂SO₄ conditions, and particularly, the expression level of ugta1 encoding UDP glucosyltransferase was upregulated by 14.3-fold. The results suggest that the sapl gene cluster is negatively involved in the production of SLs in the case of (NH₄)₂SO₄ by restraining the expression of the key genes involved in SLs synthesis. The Δsapl strain is an excellent producer of high-titer and high-yield acidic SLs.

非致病性酵母 Starmerella BombicolaCGMCC 1576 是一种高效的槐糖脂 (SL) 生产商。内酯SLs主要用酵母提取物生产，酸性SLs主要用硫酸铵生产。天然产生的 SL 是各种内酯和酸性 SL 的混合物。通常，SL混合物在技术上没有很好的分离，分离成本较高。为了降低分离成本，通过发酵液的蛋白质组学分析，鉴定了四种分泌型天冬氨酸蛋白酶样蛋白。S.bombicola在不同的氮源条件下。四种蛋白质的编码基因，即树液1, 树液2, 树液3， 和 树液4，具有高序列相似性（超过 55%）并包含在基因簇中。与酵母提取物相比，(NH ₄ ) ₂ SO ₄上四种基因的表达显着上调。将四个基因一起删除以产生菌株Δ树液. 以 Δ 表示的 SL 滴度树液以(NH ₄ ) ₂ SO ₄为氮源发酵5天后达到60.71 g/L，比野生型菌株增加90%。酸性SLs的浓度为55.84 g/L，占SLs总量的92%。来自葡萄糖的 SLs 的产量 (g/g) Δ树液为 0.78，远高于野生型菌株（0.47）。然而，在 Δ 中没有观察到 SLs 产量的增加树液在酵母提取物条件下。与野生型菌株相比，SLs合成关键基因的表达水平在Δ中均不同程度上调树液(NH ₄ ) ₂ SO ₄条件下，特别是ugta1编码 UDP 葡糖基转移酶的 14.3 倍上调。结果表明，树液在(NH ₄ ) ₂ SO ₄的情况下，基因簇通过抑制参与SLs合成的关键基因的表达而负面参与SLs的产生。Δ树液 菌株是高滴度和高产量酸性 SL 的优秀生产者。