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Biomedical subjects

A G Fredrickson

Publications and source records attributed to A G Fredrickson.

25 records · Page 2Linked to original sources
PubMed1972

Predator-prey interactions of Dictyostelium discoideum and Escherichia coli in continuous culture.

Dictyostelium discoideum and Escherichia coli were aerobically propagated in mixed continuous culture in a predator-prey relationship, and the effects of temperature and holding times were examined. Oscillations developed in the concentration of glucose, the limiting substrate for E. coli, and in the densities of the two populations, but eventually steady-state populations were reached. The experimental data were analyzed according to the Lotka-Volterra model for prey-predator relationships and by the Monod model for saturation kinetics. A comparison of the adequacy of the two models in describing predation is given.

Aerobiosis↗
PubMed1970

Automated counting of microbial colonies.

The time required for direct counting of colonies on agar plates for estimating population density of viable microorganisms has precluded studies requiring measurement of such a parameter. Bowman, Blume, and Vurek have described a photo-electrical capillary tube scanner which automates the counting. Results obtained with an instrument similar to that of Bowman et al. have been intensively analyzed with respect to precision and accuracy. The sources of "errors" have been ascertained, and the instrument's potentialities and limitations are discussed.

Automation↗
PubMedDate not supplied

Selective synchronization of Tetrahymena pyriformis cell populations and cell growth kinetics during the cell cycle.

A selection synchronization technique based on ingestion of tantalum particles has been applied to obtain synchronized cultures of the filter feeding ciliate Tetrahymena pyriformis. Cell concentrations and cell volume distributions of synchronized cell populations have been monitored for more than four average generation times. A simple curve-fitting method has been used to decompose the cell volume distributions of a synchronous population into two populations representing cells before and after cell division. In this way, the time course of the growth of an initially synchronous culture is decomposed into the growth of successive generations. The data indicate that at any given time only two generations of cells are present in significant numbers. The measured cell volume distributions show that T. pyriformis has a complicated growth pattern during the cell cycle. Newborn T. pyriformis cells do not grow significantly at the beginning of the cell cycle. After the nongrowing stage, cells start growing in a possibly exponential rate before cells enter into a second nongrowing stage. The second nongrowing stage lasts until cell division. The presented data demonstrate that growing cell populations can be viewed as the composite of cells belonging to different generations. This concept has important implications for solving corpuscular models of cell growth.

Animals↗