EVIDENCE FOR 2 DOMAINS OF GROWTH TEMPERATURE FOR THE PSYCHROTROPHIC BACTERIUM PSEUDOMONAS-FLUORESCENS MF0

The variations in the maximal specific growth rate of the psychrotroph ic bacterium Pseudomonas fluorescens MFO with respect to temperature w ere studied between 0 and 30 degrees C (optimal for growth). The Arrhe nius plot showed a drastic change in slope at the intermediate tempera ture of 17 degrees C. Over the cold domain from 0 to 17 degrees C, the temperature characteristic was twofold higher than over the suboptima l domain from 17 to 30 degrees C. The macromolecular composition of ex ponentially growing cells was invariant over the entire range from 0 t o 30 degrees C. Variations of temperature and growth rate were indepen dently investigated through chemostat experiments in order to characte rize their respective effects on cell macromolecular composition and s ize. The effect of growth rate in this psychrotrophic strain is identi cal to that of all other bacteria assayed so far. In contrast, an orig inal biphasic variation of total protein concentration was demonstrate d in strain MFO with respect to temperature, with a maximum at 17 to 2 0 degrees C, Indeed, increasing the temperature in the chemostat resul ted in a biphasic decrease in the net protein production rate: a very slight decrease below 17 degrees C and a much larger decrease from 17 to 28 degrees C. These results could signify an increase in the cellul ar protein degradation rate with increasing temperature, especially ab ove 17 degrees C.