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Microbial lipids have a great similarity to the lipids obtained from plants and animals. Triacylglycerol is the storage lipid in most of eukaryotic cells; this characteristic attracts a lot of attention for using these lipid sources in biodiesel production. Accumulation of neutral lipid composed of triacylglycerol and sterylster is an induced response to environmental stresses in many living organisms. In this situation lipid accumulates as intracellular lipid bodies in yeast cells. Production of microbial oil has more cost than plant’s oil. In this case, reducing the cost of this process must be done by optimization of culture conditions to reach higher production yield. In this study the effect of physical parameters on lipid production of two oleaginous yeasts: Yarrowia lipolytica M7 and Candida sp. was investigated. The mentioned parameters were pH range of 4-7; centrifugation rates of 100, 150, 200 rpm; temperature of 15, 25, 35 and 45ºC and times of incubation of 24, 48, 72 and 96 h. Temperature and time of incubation had a significant effect on lipid production by these strains and optimization of them resulted in increased production of lipid from 25% to 34% in Yarrowia lipolytica M7.

In this study, the factorial optimization method and designing of experiments by the Taguchi method were applied for optimization of lipid production by a native oleaginous yeast Rhodotorula spp. strain Yr2. The factors investigated were temperature, aeration, nitrogen source, carbon source, pH and incubation time. Based on results obtained by factorial optimization method, maximum production (8.9 g/L) was achieved with ammonium sulfate (1g/L) as nitrogen source, glucose (90g/L) as carbon source, at 25°C, aeration speed of 150rpm, incubation time of 96h and at pH 6. Whereas using the Taguchi method, the predicted optimal conditions were ammonium sulfate (1g/L) as nitrogen source, glucose (75g/L) as carbon source, at 25°C, aeration speed of 150rpm, incubation time of 72h and at pH 6.5. The amount of lipid production predicted by the software under these conditions was 11.052 g/L. and in the predicted case, 95% of the predicted value was achieved (10.49 g/L). The ANOVA results obtained with the Taguchi design showed that time; the amount of carbon, temperature, pH and nitrogen levels, respectively had the highest effects on lipid production in descending order. In conclusion, the application of the Taguchi method in compared with one factorial method led to increased lipid production by 1.59 g/L or 18%.

Micro-organisms such as bacteria, yeasts, molds and algae that accumulate lipid more than 20% of their biomass are called oleaginous. Microbial lipid has a lot of similarity to the oil obtained from plants and animals. Microbial lipids are renewable sources that can use for different purposes such as biodiesel production. Production of oil from yeasts has more advantages than plant’s oil. According to this, isolation of oleaginous yeast with high ability of lipid production is very valuable. In this investigation 176 yeasts were isolated. Between them 68 lipid producing yeasts were found that they were isolated from 34 soil samples. The strains were screened by an enrichment technique in glycerol and then Sudan black staining. After extraction of lipid by Bligh & Dyer method, best strain was selected which has lipid quantity, dry biomass and lipid productivity of 10.97g/l, 18.84g/l and 58.2% in optimized condition. Extracted lipid was analyzed by thin layer chromatography and FTIR spectroscopy.