Abstracts Biological Sciences

Temperature-salinity effects on net protein synthesis and viability of Vibrio marinus mp-1, an obligately psychrophilic marine bacterium

by Mary Faith Cooper

The relationship of temperature and salinity to protein synthesis was determined for cells of Vibrio marinus, MP-1. Protein synthesis was measured by the incorporation of radioactive proline into hot trichloroacetic acid precipitable material. At all salinities protein synthesis occurred at 15°C and 20°C but not at 25°C. The critical temperature of the lesion in protein synthesis increased with increasing salinity of the growth medium. A significant inhibition of protein synthesis occurred at 22°C at a salinity of 25%₀, but no inhibition of protein synthesis occurred at a salinity of 35%₀ until the cells were incubated for 20 minutes at 24°C. The possibility that the thermal lesion involved precursor accumulation mechanisms rather than protein synthesis at salinities between 25%₀ and 35%₀ was eliminated by determining the uptake of labeled proline by whole cells. At 40%₀, the uptake of extracellular amino acids was inhibited at 24°C and preceeded the inhibition of precursor into protein. RNA synthesis studies were determined at incubation temperatures inhibitory to protein synthesis. RNA synthesis was measured by the incorporation of radioactive uracil into cold trichloroacetic acid precipitable material. Total RNA synthesis continued for 50 minutes at 22°C in growth media at salinities between 15%₀ and 35%₀. At a salinity of 40%₀, incorporation of uracil into RNA decreased after 20 minutes of cell incubation at 22°C. At growth medium salinities between 15%₀ and 30%₀, total RNA synthesis continued at 15°C and 22°C, but cellular protein synthesis was inhibited by either temperature or salinity effects. Studies of cell viability loss at 22°C and 25°C in growth media at salinities of 25%₀ and 35%₀ showed that the onset of cell death occurs simultaneously with thermal inhibition of protein synthesis. The death of cells occurs more rapidly as the salinity of the growth medium is lowered and as the temperature of cell incubation is increased.