The Effect of Hydrostatic Pressure and Growth Temperature on the Growth and Membrane Composition of a Barotolerant Pseudomonas sp. Isolated from the Deep-sea Environment
Hiroyuki KANEKO*, Akira INOUE, and Koki HORIKOSHI
The DEEPSTAR group, Japan Marine Science and Technology Center, 2-15 Natsushima- cho, Yokosuka, 237, Japan
A barotolerant bacterium was isolated from deep-sea sediment in the Japan Trench, at a depth of 4418 m. The isolate was identified on the basis of standard biochemical and morphological tests as being of the genus Pseudomonas. The strain exhibited good growth in the temperature range of 10-40℃ at atmospheric pressure (0.1 MPa).
First, we investigated the profile of growth at 30℃. The microorganism was able to grow in the range of 0.1 to 60 MPa. The specific growth rates determined by measuring the optical density at 660 nm were 0.22 hr-1 '(at 0.1 MPa) to 0.04 hr-1 (at 60 MPa), and the optical densities at stationary phases were approximately 1.2 (at 0.1 - 40 MPa), 0.5 (at 50 MPa) and 0.2 (at 60 MPa).
To study the effect of hydrostatic pressure on the membrane fatty acid and phospholipid composition of the bacteria, the inner and outer membranes of the strain were separated and collected. It is generally said that growth temperature and hydrostatic pressure effects the composition and fluidity of the membrane, and that membrane fluidity is maintained by altering the proportion of unsaturated fatty acids in the phospholipids (1).
However, there was no significant difference in the composition of membrane fatty acids and phospholipids of the bacteria at any hydrostatic pressure, although the concentrations of unsaturated fatty acids in this microorganism were relatively high (about 80%) at all hydrostatic pressures at which the cells were able to grow well. This result indicated that hydrostatic pressure does not effect the fatty acid composition of all bacteria.
Here is a similar example: There are psychrotrophic Pseudomonas spp. with very high percentage of unsaturated fatty acids (about 60 - 80%) at various growth temperatures (2). This provides an example that growth temperature does not effect the fatty acid composition of all bacteria.
Secondly, we investigated the bacteria's growth profile at 10℃. The growth rate of the bacteria was very slow at 10℃. The doubling time was about 0.88 days (that meant the specific growth rate was 0.033 h-1) grown at 0.1 MPa. But, final optical
