Physiological Effects of Elevated Hydrostatic Pressure on Yeast
-A Study in "Barophysiology"-
Fumiyoshi ABE*, and Koki HORIKOSHI
The DEEPSTAR group, Japan Marine Science and Technology Center, 2-15 Natsushima-cho, Yokosuka 237, Japan
Hydrostatic pressure is a distinctive feature of the deep-sea environment and this thermodynamic parameter has a potentially disruptive effect on living organisms. There have been many reports concerning "barophilic" or "barotolerant" deep-sea bacteria which can grow under high hydrostatic pressure.
We have been analyzing the physiological effects of non-lethal hydrostatic pressure (<100 MPa) on yeast during research into a new experimental field, "Barophysiology". We are focusing on cell growth, cellular metabolisms and functions of organelles. The yeast vacuole is an acidic organelle, maintaining low pH through the function of vacuolar H+-ATPase (V-H+-ATPase) on its membrane. Acidification of vacuoles is essential for the activity of vacuolar enzymes, protein transport and cytoplasmic ion homeostasis. Recently, we found that the vacuolar pH, determined using a pH-sensitive fluorescence dye, (carboxyfluorescein, CF), was reduced by elevated hydrostatic pressure (1-4). A vma3 mutant defective in vacuolar acidification showed no reduction of vacuolar pH when hydrostatic pressure was applied (3, 4). The result indicates that the transient vacuolar acidification induced by elevated hydrostatic pressure is mediated through the function of V-H+-ATPase. The pressure-induced acidification of vacuoles was remarkable in the presence of fermentable sugars as carbon sources, suggesting that the CO2 generation was involved in the process (3, 4). We consider the pressure-induced acidification from the two points: (i) cytoplasmic pH homeostasis (ii) chemical reactions of low molecular weight compounds under hydrostatic pressure. To maintain a favorable cytoplasmic pH, the yeast vacuoles may serve as proton sequestrants under hydrostatic pressure.
1. Abe, F. and Horikoshi, K. (1995). FEMS Microbiol. Lett., 130, 307-312.
2. Abe, F. and Horikoshi, K. (1996). High Pressure Bioscience and Biotechnology ,13, 53-58.
3. Abe, F. and Horikoshi, K. (1997). Extremophiles., 1, 89-93.
4. Abe, F. and Horikoshi, K. (1997). High Pressure Research in the Bioscience and Biotechnology, 209-212.
