Increase of the ATP-dependent phosphoenolpyruvate carboxykinase activity in Sinorhizobium meliloti (Rhizobium meliloti) during hypothermic environmental conditions

Sinorhizobium meliloti growth is affected when the incubation temperature is lower than 22°C. In culture media containing glucose or fructose (1%, w/v), the doubling time at 19°C was about 6.25 h during the exponential growth phase, while it was 2.75 h at 30°C; at 17°C it was three-fold higher than at 30°C. Modifications in the bacterial metabolism explain the doubling time increase when bacteria are incubated at low temperature. We determine here, the phosphoenolpyruvate carboxykinase (PEPCK) activity increases when S. meliloti cells first grown at 30°C are shifted at 17°C and incubated for 10 h at this low temperature; we noted the PEPCK activity was three-fold higher in cells incubated in media containing glucose and shifted from 30 to 17°C than in cells maintained at 30°C, while it was only 1.5-fold higher in cells grown in media containing fructose.