Aggregation of Escherichia coli B/r A during agar filtration: Effect on morphometric measurements

Abstract

We have investigated the phenomenon of particle aggregation in a sample of 71,038 Escherichia coli B/r A cells in balanced exponential growth, during preparation for electron microscopy by agar filtration. The bacteria were photographed in a transmission electron microscope and the dimensions and spatial relationships among all the members of each aggregate were recorded using an interactive image processing system. The proportion of aggregated cells, 22%, is much greater than that found by direct count in a light microscope (7%), implying that most aggregation takes place during the preparation stages. The aggregated cells are about 1% narrower than the free cells, because of mutual compression, and 1.5% longer, because of a selection bias in favor of longer cells. From a statistical analysis of the data, we conclude that the clustering of cells into aggregates in the course of sample preparation is the result of random encounters during the settling on the collodion membrane and of the changing surface tension during the drying process. A method is proposed to correct morphometric measurements for the distortion caused by cellular aggregation of this kind.0 1992 Wiley-Liss, Inc.

Dimensional regulation of cell-cycle events in Escherichia coli during steady-state growth

“…Later, electron-microscopic studies confirmed the essential findings and reported only small, apparently random fluctuations in diameter (Harvey & Marr, 1966). Trueba & Woldringh (1980) observed that the average diameter of slow-growing cells decreased gradually as a function of cell length prior to constriction, rising again during the constriction process ; this was later corroborated by Vardi & Grover (1992) elaborate analysis of more than 55 000 cells. Trueba & Woldringh (1980) inferred from their findings that the diameter of individual cells decreases systematically during their elongation, possibly because of the maintenance of a constant surface-to-volume ratio during the cell cycle.…”

“…Schematic representations of the diameter-length correlations r DL and the * Differences between  V and corresponding  L and  D are very highly significant (P 0n001) in all cases, as determined by the test proposed by Miller (Zar, 1999). † Microscopically selected cells : data obtained by Vardi & Grover (1992) diameter-volume correlations r DV as predicted by each of the models are indicated in Fig. 1.…”

“…In Table 3, the theoretical predictions are compared with experimental values obtained from the electronmicroscopic measurements of Vardi & Grover (1992).…”

“…‡ Probability that population correlation coefficient is zero (alternative hypothesis negative for diameter-length correlations, positive for diameter-volume correlations) : , P 0n05 ; *, 0n05 P 0n01 ; **, 0n01 P 0n001 ; ***, P 0n001. § Microscopically selected cells : data obtained by Vardi & Grover (1992) from electron-microscopic measurements of cells growing in steady state (doubling time 113 min). R Selected by membrane elution : data obtained from phase-contrast microscopic measurements ; scatter plot presented in Fig.…”

“…Clearly, the Length model and the Volume model make very different predictions about the correlations between the various dimensions of the cell and about the variations in these dimensions at all regulated cell-cycle events. We have therefore examined both previously published (Vardi & Grover, 1992) and newly acquired data in the light of these two models and carried out extensive simulation studies in an attempt to distinguish between them.…”