Calorimetric Studies on the Growth Behavior of Yeast under Some Compressed Hydrocarbon Gases

In this study, the inhibitory effect under compressed hydrocarbon gases on yeast growth was investigated quantitatively by microcalorimetry. The growth thermograms (heat output - incubation time curve) were obtained during incubation of yeast under various compressed hydrocarbon gases. When the gas pressure increased, the curves of thermograms shifted to the right, indicating an obvious inhibitory action on the yeast growth. After quantification of growth inhibition at various pressures, we determined the 50% inhibitory pressure (IP₅₀) and the minimum inhibitory pressure (MIP) values as indices which represent toxic potency of each gas. The lower the IP₅₀ and MIP values, the greater the growth inhibitory effects of the gas. Based on these values, the inhibitory potency of the gases increased in the order: methane < ethane < propane < i-butane < n-butane. In addition, the toxicity of some hydrocarbon gases was found to be correlated to their hydrophobicity. These results suggest that hydrocarbon gases interact with some hydrophobic region of the cell membrane, resulting in modification of membrane structure and function. However, no evidence was obtained in the yeast treated with compressed hydrocarbon gases as to the membrane damage. Therefore, we investigated the effects of hydrocarbon gases on the leakage of 260 nm absorbing material from treated cells. The release amount of 260 nm absorbing material increased with increasing pressure. This indicates that hydrocarbon gases affect the plasma membrane, particularly the nuclear membrane. Furthermore, we examined the effects of hydrocarbon gases on the morphology of the yeasts by scanning electron microscopy. Scanning electron microscopy showed that yeasts when exposed to compressed hydrocarbon gases undergo a dramatic morphological change that includes invagination of the cell surface.