An Outline of the Pattern of Bacterial Generation Times

Abstract

SUMMARY: The generation times of four species of organisms have been measured, each under several sets of conditions : Aerobacter cloacae, Serratia marcescens, Streptococcus f aecalis and Pseudomonas aeruginosa. Minor variations in the experimental conditions appear to affect the mean generation time less in large samples than in small. This can be explained as a result of association between the generation times of closely related organisms. Positive correlation between the generation times of sisters, cousins and perhaps second cousins shows that the influence of an ancestor is felt through two or three generations. The observed correlation between mothers and daughters is usually small, probably because of bias due to the interval between fission of cytoplasm and fission of cell wall. The coefficient of variation of generation time is not a constant for the species but it is stable under given circumstances. It is possibly related systematically to the chemical complexity of the growth medium. In unhampered growth, less than 1% of the organisms produced are non-viable. There is positive association between the viabilities of sisters, and between the viability of an organism and the generation time of its mother. The distribution of generation times can be represented by a Pearson Type I11 or else a Pearson Type V distribution ; both are convenient in applications.The generation time of an individual is considered to be determined partly by molecular accidents, partly by heredity.In a previous paper on this subject (Powell, 1955), I gave an account of some preliminary work designed to test and compare the hypotheses of Rahn (1932) and Kendall (1948, 1952) about the causes of variability in the generation times ( 7 ) of individual bacteria. It turned out that a comparison of the observed distributions of 7 with those predicted by the hypotheses was not altogether satisfactory, and I suggested that a further test might be made by determining the effect of alterations in temperature and growth medium on the coefficient of variation of 7. At the same time I concluded that such experiments should await improvements in observational technique. There appeared to be a possibility that the relevance of the observations was altogether vitiated by ' delayed fission ', that is, by the lapse of an appreciable and variable interval between the termination of the processes considered by Rahn and Kendall, and the overt occurrence of fission.The results which I now present consist of generation time measurements on unicellular organisms of four species-Aerobacter cloacae, Serratia marcescens, Streptococcus faeculis and Pseudomonas aeruginosa-each under several different growth conditions. The undertaking was originally encouraged by the development of an improved culture chamber (Powell, 1956a), which would permit much greater accuracy in the determination of times of fission. At first, I hoped that the results would be of enhanced diacritical value, but it soon became clear that the generation times of bacteria do not depend ...

Persistence of Staphylococcus aureus in Penicillin in vitro

“…In general, bacteria which survive the action of various harmful substances may not transfer this ability to their progeny (Eddy & Hinshelwood, 1953), After survival in acid, for example, closely related cells share similar resistance for several divisions, but this is not propagated through an overnight subculture (Powell, 1958). In populations treated withvarious chemicals, heat, or radiation the 108 organisms/ml.…”

Characterization of dependencies between growth and division in budding yeast

“…Indeed, correlation and biological lineage analysis have been intertwined at least as far back as the development of the correlation coefficient by Galton, Pearson and co-workers [14,[19][20][21][22][23]. Statistical models of correlation in cellular characteristics have been successfully applied to bacterial and mammalian cell lineage data [24,25].…”

“…In multicellular systems, coordination of division among cells has important implications for higher-scale phenomena like development, differentiation and tissue organization [14 -18]. In unicellular organisms like the budding yeast S. cerevisiae, inter-cycle dependencies between growth and division are also plausible [19] and might affect more classically studied intra-cycle dependencies or characteristics. For example, a mother cell with some advantage in cell division or growth might transmit that advantage to her progeny, resulting in a fast-dividing or fast-growing daughter cell.…”

Dynamic variability in apoptotic threshold as a strategy for combating fractional killing

“…13 Similarly, fractional killing of a cancer cell population by chemotherapy depends on 14 arrival time: the shorter the arrival time is, the more are the cells killed, indicating 15 the therapeutic efficacy is better. In short, timing precision and arrival time are two 16 important indices measuring the event timing. Characterization of control strategies that 17 reduces variability in the event timing or/and shortens arrival time is critically needed 18 to understand both reliable functioning of diverse intracellular pathways that relies on 19 precision in the timing and drug efficacy that depends on the time that drug-dependent 20 regulatory proteins reach threshold levels.…”

“…On the one hand, 2 some important cellular processes depend on precision in the timing of key intracellular 3 events, e.g., cell fate decision presumably requires a precise control of gene expression 4 timing [2][3][4][5][6][7][8][9][10][11][12][13][14][15], and the controls of cell cycle and circadian clocks require timing precision 5 that can be crucial for the correct physiology [16][17][18][19][20][21][22][23][24]. Most of these processes are based 6 on gene expression, e.g., an activated gene may be required to reach in a precise time threshold level of p53 to execute apoptosis and this threshold increases with time [26].…”