Heavy oils (mainly alkanes) over-production from inulin by Aureobasidium melanogenum 9-1 and its transformant 88 carrying an inulinase gene

After screening the yeast-like strains isolated from a mangrove ecosystem at Dongzaikang, Haikou, Hainan Province of China, it was found that Aureobasidium melanogenum 9-1 could produce 28.5 g l−1 of crude heavy oils when it was grown in the medium containing 120.0 g l−1 glucose. It is interesting to note that when grown in a medium containing 160.0 g l−1 inulin, it could produce 30.2 g l−1 of crude heavy oils. After an inulinase gene from Kluyveromyces marximus was actively expressed in A. melanogenum 9-1, a transformant 88 could produce 70.8 U ml−1 of inulinase activity within 72 h whereas A. melanogenum 9-1 only produced 17.4 U ml−1 of inulinase activity. During the 10-L fermentation, A. melanogenum 9-1 could yield 38.24 g l−1 of the crude heavy oils and cell dry weight was 25.2 g l−1 within 120 h while the transformant 88 could yield 43.0 g l−1 of the crude heavy oils and cell dry weight was 24.7 g l−1 under the same conditions. However, 9.97 g l−1 of total sugar and 2.55 g l−1 of reducing sugar were left in the culture of A. melanogenum 9-1 while only 3.2 g l−1 of total sugar and 0.48 g l−1 of reducing sugar were maintained in the culture of the transformant 88. The extracellular heavy oils produced by A. melanogenum 9-1 contained 87.12% alkanes and 12.88% fatty acids whereas the extracellular heavy oils produced by the transformant 88 contained 89.8% hydrocarbons and 10.2% fatty acids. In contrast, the intracellular oils produced A. melanogenum 9-1 contained 99.3% fatty acids and 0.7% alkanes while the intracellular oils produced by the transformant 88 contained 95.44% fatty acids and 4.56% alkanes. All these results showed that most of the secreted heavy oils were alkanes and most of the synthesized alkanes were secreted into the medium while most of the synthesized fatty acids remained in the cells.