Thermal analysis for differentiating between oleaginous and non-oleaginous microorganisms

The potential of thermal analysis for differentiating between oleaginous and non-oleaginous microorganisms was investigated using thermogravimetry (TG) and differential thermal analysis (DTA). The model oleaginous microorganisms used in the present study were the fungi, Mortierella alpina IFO32281 and Mortierella alliacea YN-15, the unicellular alga, Aurantiochytrium sp. CB 15-5, and the yeast, Rhodosporidium toruloides DMKU3-TK 16. Escherichia coli JM109, Rhodococcus opacus B-4, and Saccharomyces cerevisiae were used as the control non-oleaginous microorganisms. In simultaneous TG and DTA, the furnace temperature was linearly increased from 30 to 280 °C, decreased to 30 °C, linearly increased from 30 to 360 °C, and then isothermally held at 360 °C for 30 min. This two-step linear temperature program was effective in resolving overlapping exothermic peaks in the DTA curves in the temperature range from 280 to 360 °C. Heat evolved from a microbial sample was estimated from the area under the exothermic peak between 280 and 360 °C using indium as a standard material. There was a linear relationship between the exothermic heat and total lipid content of the tested microorganisms. Exothermic heat per dry sample mass (kJ/g) in the temperature range from 280 to 360 °C is a promising measure for differentiating between oleaginous and non-oleaginous microorganisms.