HOMEOVISCOUS ADAPTATION IN A PSYCHROPHILIC BACTERIUM, VIBRIO SP. STRAIN ABE-1

Abstract

The phase separation of total phospholipids and four individual phospholipids from a psychrophilic bacterium, Vibrio sp. strain ABE-1 (Vibrio
ABE-1), was examined with methyl-9, 11, 13, 15-all-trans-octadecatetraenoate (methyl-t-parinarate) as a fluorescent probe. Phase separation of total phospholipids from the inner and outer membranes always occur at temperatures lower than the respective growth temperatures (0°C, 10°C, or 20°C). Moreover, in both inner and outer membrane phospholipids, fluorescence anisotropies calculated from polarization ratios were strikingly similar to one another when they were analyzed at the same temperatures as the respective growth temperatures. These results show that Vibrio ABE-1 can keep their membranes fluid state at least in the temperature range from 0°C to 20°C. Preservation of the membrane fluidity at low temperature seems to be attributable in this bacterium to an extremely high content of hexadecenoic acid (16:1) in the membrane phospholipids, especially in phosphatidyl ethanolamine and phosphatidyl glycerol.