Overexpression of a pyruvate carboxylase gene enhances extracellular liamocin and intracellular lipid biosynthesis by Aureobasidium melanogenum M39

摘要

The pyruvate carboxylase-encoding PYC1 gene from the yeast strain Aureobasidium sp. P6, which is a polymalate over-producer, was actively overexpressed in the marine-derived yeast Aureobasidium melanogenum 9-1, which is a heavy oil (liamocin) producer. The resulting PYC1-over-expressing transformant M39 produced 35.3 +/- 1.2 g/l liamocins and 24.6 +/- 0.5% (w/w) intracellular oil, and its cell dry weight was 17.0 +/- 1.6 g/l. On the other hand, wild-type strain 9-1 only produced 27.4 +/- 0.3 g/l liamocins and 22.6 +/- 0.8% (w/w) intracellular oil and had a cell dry weight of 15.3 +/- 2.0 g/l within 168 h. The results suggested that the over-expression of the PYC1 gene enhanced the biosynthesis of liamocins and intracellular lipids in transformant M39 due to the enhanced biosynthesis of citric acid, which could be the precursor for the biosynthesis of the intracellular lipids and extracellular liamocins. During fermentation, 43.04 +/- 1.2 g/l of extracellular liamocins, 17.7 +/- 0.5 g/l of cell dry weight and 23.8 +/- 0.2 g/l of intracellular lipids were produced by transformant M39 within 156 h, leaving 2.1% reducing sugar in the fermented medium. Moreover, the strong alkaline hydrolysis products of the extracellular liamocins mainly contained 5-hydroxy-2-decenoic acid lactone (92.1 +/- 0.3%), hexadecanoic acids (C-16:0 , 3.3 +/- 0.04%), octadecadienoic acids (C-18:2, 1.0 +/- 0.2%) and octadecanoic acids (C-18:0, 3.6 +/- 0.01%), while the intracellular lipids mainly contained C-16:0 , C-16:1, C-18:0, C-18:1 and C-18:2 fatty acids.