Exponential growth of Escherichia coli B/r during its division cycle is demonstrated by the size distribution in liquid
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© Springer-Verlag 1998
O R I G I N A L PA P E R
F. J. Trueba · L. J. H. Koppes
Exponential growth of Escherichia coli B/r during its division cycle is demonstrated by the size distribution in liquid culture
Received: 12 November 1997 / Accepted: 29 January 1998
Abstract The Collins and Richmond equation was used to analyze the growth of individual bacterial cells. Birth size was derived from the size of deeply constricted cells in the sample. The analysis was applied to normalized and pooled data from electron micrographs of Escherichia coli showing that cellular length, surface, and volume do not grow linearly as reported before. We present evidence that bacteria grow exponentially during the division cycle, which is consistent with previous proposals. Our results confirm previous incorporation studies that demonstrate basically exponential growth patterns for cell mass during the division cycle. Key words Escherichia coli · Cell size distribution · Collins and Richmond · Kinetics of growth
Introduction Various proposals for cell growth during the bacterial divisional cycle have been postulated: linear models (Kubitschek 1968, 1969, 1970; Koppes et al. 1987; Kubitschek and Pai 1988) and exponential patterns (Koch 1966; Koppes et al. 1987; Cooper 1988a, 1991). In order to ascertain one or the other alternative, individual cellular growth has been observed by light microscopy (Schaechter et al. 1962; Adler and Hardigree 1964; Errington et al. 1965; Donachie et al. 1976; Eksztejn and Varon 1977; Tzagoloff and Novick 1977; Westling-Häggström et al. 1977; Miyata et al. 1978; Rolinson 1980). The F. J. Trueba1 · L. J. H. Koppes2 Institute for Molecular Cell Biology, University of Amsterdam, Biocentrum, Kruislaan 316, NL-1098 SM Amsterdam, The Netherlands Present addresses: 1 Teseo, 40, E-28027 Madrid, Spain Tel. +34-1-3204644; Fax +34-1-3206812 2 Plantage Muidergracht 14, NL-1018 TV Amsterdam, The Netherlands Tel. +31-20-5256219; Fax +31-20-5256271
results concur with each other, showing that cells of widely different bacterial species grow continuously between divisions. But the minuteness of bacteria makes it difficult, using optical methods, to discriminate between different patterns of individual cellular growth. At variance with light microscopy, early biochemical studies of the incorporation of radioactive precursors have consistently demonstrated that growth is surely not linear (Ecker and Kokaisl 1969; Zusman et al. 1971). This result has been confirmed by membrane elution experiments showing that growth is clearly exponential (Meijer et al. 1979; Koppes et al. 1980; Cooper 1988b). Collins and Richmond (1962) have invented a method of analysis based on the distribution of cell sizes at any given instant rather than on following cells in time. Their formula has also been derived by Ramkrishna et al. (1968). The CR-method has been applied to several organisms with inconclusive results (Collins and Richmond 1962; Harvey et al. 1967; Anderson et al. 1969; Marr et al. 1969; Zusman et al. 197l; Cullum and Vicente
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