Studies On Heavy Oil Production By The Aureobasidium Melanogenum Strain P5

With the development of economy, the research on biofuel production has received increasing attention, such as fuel ethanol and biodiesel,while they have a number of drawbacks in the production and use. such as high production costs, low energy density, low calorific value. Microbial lipids usually occur within the cells from which lipid extraction process is complex, so there are some restrictions on the production of biodiesel. Alkanes widely found in nature, are similar to main compositions in the petroleum in structure and properties. Bacteria, fungi and algae can produce intracellular and extracellular hydrocarbons, thus using microorganism to produce extracellular hydrocarbons can directly replace the main composition of paraffin oil. Whether marine yeast can produce extracellular alkanes is the main contents of this study.After 100 marine yeast strains which were isolated from mangrove ecosystem were screened for their ability to produce heavy oil, the strain P5 was found to produce the highest extracellular heavy oil and its concentration in the culture was 22.5 g/1. The strain P5 was finally identified to be a member of A. melonogenum through the results of morphology observation, physiological and biochemical reactions and molecular biology. After optimization of the medium for heavy oil production and cell growth by the yeast strain P5, it was found that 12% glucose,0.1% corn steep liquor,0.1% NH4NO3,0.01% KH2PO4,0.02% MgSO4·7H2O,0.05% KCl were the most suitable medium for heavy oil production. After 7 days, the yeast strain P5 could produce 31.8 g/1 heavy oil and the cell growth was 22.7 g/1. During 10-1 fermentation, the yeast strain P5 produced 32.5 g/1 of heavy oil and cell mass was 23.0 g/1 within 168 h.GC-MS analysis on heavy oil compositions showed that it contained long chain alkanes(≥C20), mainly hexacosane, heptacosane and octacosane accounting for 8.65%、8.76% and 32.31% respectively. This is the first time to show that the yeast can produce extracellular long chain alkanes. Although it can not directly as a feedstock for diesel and gasoline, it can be used as the raw material using existing oil refining process by catalyst to manufacture different length of carbon chain of alkanes. After analyzing six possible alkane biosynthesis pathways in different organisms, it was found that the alkane biosynthesis pathway in A.melanogenum may be similar to that in plant because they have similar enzymes such as CER6, CER1 and CER3 genes which have been found to be involved in long chain hydrocarbon biosynthesis in plants. However, this must be confirmed using genetic tools. The intracellular lipids contained C16:0(21.2%), C16:1(2.8%), C18:0(2.9%), C18:1 (39.8%), C18:2(33.3%) that were similar to those of the vegetable oils, so the intracellular lipids was a good feedstock for biodiesel production,but it didn’t contain long chain hydrocarbons.