Interdivision Time Research Articles

Residual thymidine incorporation in the presence of chloramphenicol in synchronous cultures of Escherichia coli B-r.

Escherichia coli B/r ATCC 12407 which grew synchronously with interdivision times of 45 and 85 min were exposed at intervals to chloramphenicol (200 mug/ml) and [(14)C]thymidine for short or long (residual) periods. The results suggested that the pattern of residual thymidine incorporation in 85-min cells yielded an estimate of the length of the D period rather than the time of initiation of chromosome replication.

Genealogies of clones of diploid fibroblasts: Cinemicrophotographic observations of cell division patterns in relation to population age

Direct assessment of cell division patterns of human diploid fibroblasts (WI-38) has been achieved using techniques of time-lapse cinemicrophotography. Pedigrees of progeny cells in clones from middle and late passage WI-38 cultures are presented. The passage 28 clone exhibited a division pattern that was highly synchronous through four generations and had an average interdivision time that increased linearly from the second through sixth generations. Division was essentially logarithmic through the fourth generation. The passage 53 clone was much more variable in interdivision time, less synchronous, and less motile than the passage 28 clone. While there is considerable overlap in the interdivision times of cells of the passage 28 and 53 clones, the late passage cells generally exhibit more variation in interdivision times. The average population doubling time was 16.8 h in thepassage 28 clone and 32.0 h in the passage 53 clone.

Kinetic invetigations of biosynthesis of cellulose by Actobacter xylinum

1.1. The relation between the yield of cellulose, the weight average degree of polymerization, DPW, the time of synthesis, and the growth of the bacterial population were studied.2.2. The yield of cellulose and the bacterial population obey the same first-order reaction law with the same rate contants. DPW increases linearly with time and is inversely proportional to the corresponding interdivision time, τN, of the bacteria. Acetobacter xylinum synthesizes, besides cellulose, other compounds (probably also polysaccharides) according to the same reaction law and with the same rate constants.3.3. The results permit us to draw the following conclusions: A strict control of the synthetic processes is exerted by the bacteria. This control apparently affects the initiation of a defined number of polysaccharide chains during cell division of another event related to it. Once started, the cellulose (or polysaccharide)molecules grow independently from further divisions of the bacteria during several generation times and with a rate directed by the enzymatic activity, which in turn also directs the value of τN. 1. The relation between the yield of cellulose, the weight average degree of polymerization, DPW, the time of synthesis, and the growth of the bacterial population were studied. 2. The yield of cellulose and the bacterial population obey the same first-order reaction law with the same rate contants. DPW increases linearly with time and is inversely proportional to the corresponding interdivision time, τN, of the bacteria. Acetobacter xylinum synthesizes, besides cellulose, other compounds (probably also polysaccharides) according to the same reaction law and with the same rate constants. 3. The results permit us to draw the following conclusions: A strict control of the synthetic processes is exerted by the bacteria. This control apparently affects the initiation of a defined number of polysaccharide chains during cell division of another event related to it. Once started, the cellulose (or polysaccharide)molecules grow independently from further divisions of the bacteria during several generation times and with a rate directed by the enzymatic activity, which in turn also directs the value of τN.

Clone size variation in the human diploid cell strain, WI-38.

AbstractBy mapping the location of isolated single cells; and then counting the number of cells at each location as a function of time. it was possible to accumulate data on the growth history for each of a large group of clones. The clone size distribution, its mean and standard deviation were computed for each day in culture. Variations in schedule of medium change and time of exposure to trypsin, did not measurably affect variation in clone size. Neither could clone size variation be accounted for on the basis of (1) occurrence of nondividing cells nor (2) presence of heritable growth rate variants in the population. It is probable that clone size variation under our conditions is primarily a consequence of a highly variable interdivision time among the constituent cells.

Control of F'lac replication in Escherichia coli B-r.

The timing of replication of an F'lac plasmid during the division cycle of Escherichia coli B/r lac(-)/F'lac was examined in relation to the timing of initiation of chromosome replication. This was accomplished by measuring the induction of beta-galactosidase and the incorporation of radioactive thymidine into cells at different ages in cultures growing exponentially at various rates. In cells growing with interdivision times of 27, 36, and 55 min, the F'lac replicated at various stages in the division cycle but always at approximately the same time as initiation of chromosome replication. In cells growing with an interdivision time of 85 min, the F'lac episome replicated midway through the division cycle, whereas chromosome replication initiated at the start of the cycle. Measurements of absorbance at 450 nm per cell suggested that the F'lac replicated when the cells reached a mass which was a constant multiple of the number of episomes per cell at each growth rate. In contrast, the mass per cell at initiation of chromosome replication in cells with an 85-min interdivision time was significantly lower than this constant value. A possible explanation for the apparent coupling between F'lac replication and initiation of chromosome replication at the higher growth rates, and the lack of coupling at the lowest growth rate, is discussed.

On the average cellular volume in synchronized cell populations.

As was done by Sinclair and Ross (1969(, we consider a cellular population that consists initially (at time zero) ofN0 newborn cells, all with the same volumevo. It is assumed that the occurrence of cell division is determined only by a cell’s age, and not by its volume. The frequency function of interdivision times, τ, is denoted byf(τ). If cell death is negligible, the expected number of cells,N(t), will increase according to the laws of a simple age-dependent branching process. The expression forN(t) is obtained as a sum over all generations; thevth term of this sum, in turn, is a multiple convolution integral, reflecting the life history ofvth generation cells (i.e., the lengths of thev successive interdivision periods plus the age of the cell at timet). Assuming that cell volume is a given function of cell age, e.g., linear or exponential, and that cellular volume is exactly halved at each division, it is possible to calculate the volume of a cell with a given life history, and thus the average cellular volume of the whole population as a function of time. If at time zero the volumes differ from cell to cell, the final equation must be modified by averaging over initial volumes. In the case of linear volume increase with age, a very simple asymptotic expression is found for the average cellular volume ast→∞. The case of exponential volume increase with age also leads to a simple asymptotic formula, but the resulting volume distribution is unstable.

Synchronous growth of enteric bacteria.

Helmstetter and Cummings devised a technique of synchronization in which cells are implanted on a membrane filter and the membrane is subjected to reverse flow of liquid medium. The cells in the effluent stream have predominantly the characteristics of newborn cells. The advantage of this technique is that the population experiences a minimum of physiological stress; hence, the behavior of the synchronous culture should reflect the normal divisional cycle. The disadvantage is that strains other than Escherichia coli B/r cannot be synchronized. We have found that a modification of the method makes it possible to synchronize several strains of E. coli, including both male and female strains, as well as Salmonella typhimurium LT2. The principal difference in technique is a prolonged period (>400 doublings) of cultivation in glucose minimal medium at 30 C and at low density (<5 x 10(6) cells/ml) prior to implantation. This precaution was taken to insure that the bacterial growth population is in a steady state of balanced growth. From the resulting synchronous growth, the distribution of interdivision times has been computed; these distributions have coefficients of variation in the range 0.18 to 0.22 and are not appreciably skewed.

Inequality of Mean Interdivision Time and Doubling Time

Microbiology Society journals contain high-quality research papers and topical review articles. We are a not-for-profit publisher and we support and invest in the microbiology community, to the benefit of everyone. This supports our principal goal to develop, expand and strengthen the networks available to our members so that they can generate new knowledge about microbes and ensure that it is shared with other communities.

Kinetics of growth of individual cells of Escherichia coli and Azotobacter agilis.

Escherichia coli and Azotobacter agilis were grown in minimal media until a steady state was established. The distribution of cell size was determined electronically. From the equation of Collins and Richmond, the growth rate of individual cells was computed as a function of size. The main features of the growth of individual E. coli and A. agilis cells revealed by this work were: the specific growth rate decreased at the time of division, and both the absolute and specific growth rates increased between divisions. The frequency function of interdivision times was computed and was found to be positively skewed with a coefficient of variation of approximately 0.3. The results supported the hypothesis of Koch and Schaechter that the size of an individual cell at division is highly regulated.

Growth, cell and nuclear divisions in some bacteria.

SUMMARY: The timing of cell and nuclear division of certain enteric bacteria was determined under conditions of balanced growth. Organisms were grown in a high refractive index medium and photographed at frequent intervals with a phase-contrast microscope. This allowed an estimation of the time between successive divisions of nuclei and cells (interdivision times) and the growth rate of each individual. The interdivision times of cell and nuclear divisions had a similar degree of variation (coefficients of variation of about 20%). The interdivision times of sister cells and sister nuclei were positively correlated to a significant degree. The correlation between mothers and daughters was negative to a significant degree in some, but not all, experiments. The correlation between interdivision times of a cell and that of its corresponding nucleus was positive in most experiments. The rate of mass increase of individual cells was estimated by measuring the rate of elongation. Within the limitations of the method of observation, it could be concluded that cells grew exponentially between successive divisions. Different individuals grew with very nearly the same rate constant. The variation in size of cells at the time of nuclear and cell division was smaller (coefficients of variation of about 10%) than that of the interdivision times. Some observations on the morphological changes of nuclei during growth and division are presented.