Influence of low-temperature storage and glucose starvation on growth recovery in Escherichia coli relA and relA+ strains.

To study the influence of microgravity on bacterial growth behavior during a space mission, the special experimental conditions and the hardware environment necessitate storage of cells at low temperature, and permit a relatively short experimental period. Before this experimental period, cells have to recover their condition of steady-state growth, because it is only in this condition that the growth behavior of the flight and ground populations can be adequately compared. To meet these requirements and to obtain cells which recover rapidly their steady-state growth, we analyzed the size and shape of Escherichia coli cells during storage at 4 degrees C, with and without previous glucose starvation of the cells. It appeared that cells stored at low temperature in the presence of glucose continued to increase in average mass and assumed ovoid shapes. In addition, upon restoration of maximal growth rate at 37 degrees C, they continued to increase in size and showed a transient overshoot of their final steady-state value, which was reached after about 5 h. Cells previously starved for glucose, however, maintained their average size and rod-shape during low-temperature storage. Recovery of the starved cells was most rapid in the relA+ strain which, contrary to the isogenic relA strain, showed no overshoot and reached its final steady-state size within 2 h.