The Transition Between Different Physiological States During Balanced Growth of Salmonella typhimurium

Abstract

SUMMARY : When cultures of Salmonella typhimurium undergoing balanced growth are shifted from one medium to another, a definite pattern of rate changes is observed. Shifts from a low to a high growth rate result in a strict succession of events: RNA synthesis is immediately affected and its rate rapidly increases to that characteristic of the new medium; the increase in optical density shows a lag of a few minutes before the new rate is attained; DNA synthesis and cell division, on the other hand, continue at the old rate for appreciable periods of time and then abruptly shift to the new rates. The times at which these shifts take place are, at 37', invariably 20 and 70 min., regardless of the actual growth rates before and after the shift. This rate maintenance effect on DNA synthesis and cell division is discussed in terms of specific rate-controlling mechanisms.In the preceding paper (Schaechter, Maalnre & Kjeldgaard, 1959) we showed that the size and chemical composition of Salmonella typhimurium vary exponentially with the growth rate afforded by different media. The present paper describes the transition from one state of balanced growth to another. The terms 'balanced growth' and 'cell' as used by us, have been defined in the preceding paper. Two types of experiments were performed, both involving precisely timed changes of medium at constant temperatures; one going to a higher growth rate (shift up), and the other to a lower rate (shijt d m ) .The shift up, exemplified by going from a glucose salt medium to nutrient broth, is characterized by an orderly dissociation of the main synthetic activities. Upon addition of broth, the rates of synthesis of ribonucleic acid (RNA) and of total mass immediately increase, whereas deoxyribonucleic acid (DNA) synthesis and cell division continue at the old rate for considerable periods of time. The new state of balanced growth is reached when, after about 70 min. (at 37O), the rate of cell division abruptly changes from thepreshift value to the definitive broth rate. We interpret this 'rate maintenance effect ' as evidence for the existence of separate rate-controlling mechanisms.The shqt down is rapidly effected by filtration of, say, a nutrient broth culture and resuspension of the cells in simple defined medium. It is characterized by a period during which cell division and DNA synthesis continue in the absence of net synthesis of RNA and total mass. By the time RNA and mass begin to increase the cells have already approached the size and the composition typical of balanced growth in the simpler medium. This behaviour

Protein Synthesis, Cell Division and the Cell Cycle in Saccharomyces cerevisiae following a Shift to a Richer Medium

“…Fantes & Nurse (1977) observed that one of the first effects of the shift is a complete but transient inhibition of nuclear division. They postulate on the basis of their results and earlier work by Nurse (1975) that there is in the fission yeast a cell size requirement for entry into nuclear division and that the cell size necessary for nuclear division is set or modulated by the prevailing growth conditions. The apparent differences in the control of cell division in these two yeasts warns against extrapolation of control models to other eukaryotes.…”

Early increases in the frequency of DNA initiations and of phospholipid synthesis discontinuities after nutritional shift-up in Escherichia coli

“…Most of the classical results [5][6][7]101 were interpreted in terms of 'rate maintenance' of DNA synthesis for some 20 min after a shift-up. Cooper [30] favored the idea of an advance of the following initiation and re-interpreted older data [5] in terms of an early and gradual increase in the rate of DNA synthesis.…”

“…Most of the classical results [5][6][7]101 were interpreted in terms of 'rate maintenance' of DNA synthesis for some 20 min after a shift-up. Cooper [30] favored the idea of an advance of the following initiation and re-interpreted older data [5] in terms of an early and gradual increase in the rate of DNA synthesis. Our unpublished results, using an accurate one-step fluorimetric DNA assay on synchronized cultures [31], do not differ significantly from the classical results, in that they show a 'rate maintenance' of DNA synthesis for about 20min on the average.…”

The Use of Chemostats in Microbial Systems Biology

“…The experimental control of growth rate using chemostats was critical to the development of an understanding of how cell physiology changes with rates of growth 5,6 . However, this former mainstay of microbiological methods became increasingly obscure during the explosion in molecular biology research during the late twentieth century.…”