title: Synchronous cultures from the baby machine: anatomy of a model.
abstract: The baby-machine system, which produces newborn Escherichia coli cells from cultures immobilized on a membrane, was developed many years ago in an attempt to attain optimal synchrony with minimal disturbance of steady-state growth. In the present article, we describe in some detail a model designed to analyse such cells with a view to characterizing the nature and quality of the synchrony in a quantitative manner; it can also serve to evaluate the methodology itself, its potential and its limitations. The model consists of five elements, giving rise to five adjustable parameters (and a proportionality constant): a major, essentially synchronous group of cells with ages distributed normally about zero; a minor, random component from a steady-state population on the membrane that had undergone only very little age selection during the elution process; a fixed background count, to account for the signals recorded by the electronic particle counter produced by debris and electronic noise; a time-shift, to allow for differences between collection time and sampling time; and the coefficient of variation of the interdivision-time distribution, taken to be a Pearson type III. The model is fitted by nonlinear least-squares to data from cells grown in glucose minimal medium. The standard errors of the parameters are quite small, making their estimates all highly significant; the quality of the fit is striking. We also provide a simple yet rigorous procedure for correcting cell counts obtained in an electronic particle counter for the effect of coincidence. An example using real data produces an excellent fit.
authors.affiliation: Hubert H. Humphrey Center for Experimental Medicine and Cancer Research, The Hebrew University Faculty of Medicine, Jerusalem, Israel. norman@md.huji.ac.il
authors.forename: N B
authors.initials: NB
authors.lastname: Grover
authors.forename: C
authors.initials: C
authors.lastname: Coustère-Yakir
authors.forename: C E
authors.initials: CE
authors.lastname: Helmstetter
mesh_terms: D018929:Cell Culture Techniques / Q000379:methods*; D002455:Cell Division / Q000502:physiology; D002478:Cells, Cultured; D003470:Culture Media; D004926:Escherichia coli / Q000502:physiology*; D005947:Glucose; D016018:Least-Squares Analysis; D008954:Models, Biological; D013997:Time Factors
chemical_list: D003470:Culture Media; D005947:Glucose