Effect of Heavy Metal Ions on Microbial Oil Contents and Citric Acids Secretion in Yarrowia lipolytica

The effects of different heavy metal ions on biomass,extracellular citric acid contents,oil contents and fatty acid composition were studied. And the influences of various heavy metal ions on lipid accumulation and citric acids secretion in Yarrowia lipolytica were also studied. The results showed that cell growth was inhibited by 4 heavy metal ions(Co²⁺,Cu²⁺,Mn²⁺ and Ni²⁺),and the inhibition efficiency increased with increasing concentration of those ions. Citric acid secretion and lipid accumulation also decreased in the presence of 4 heavy metal ions except Mn²⁺. When Mn²⁺ concentration was 1.0 mmol/L,the lipids contents reached maximum value(17.6%,w/w). And maximum citric acid production achieved 6.9 g/L with the addition of 2.0 mmol/L Mn²⁺. Furthermore,heavy metal ions also affected the lipid fatty acid composition. Co²⁺ and Ni²⁺ increased the contents of saturated fatty acids and decreased monounsaturated fatty acid. Cu²⁺ promoted the increase of linoleic acid content(from 7% to 40%). This study could provide a basis for the production of microbial oil and citric acids by fermentation.