Population Growth Kinetics Research Articles

EFFECT OF TEMPERATURE ON SUSPENSION CRYSTALLIZATION PROCESSES

Abstract A mathematical analysis was carried out to examine the effect of temperature on the nucleation and growth rates in continuous suspension crystallization systems. The analysis included consideration of the population balance, mass balance, nucleation and growth kinetics, and the temperature dependence of the nucleation and growth rate constants. This study provides a reasonable basis to understand the relationships between nucleation and growth rates and such factors as supersaturation, “overall” activation energies, and the kinetic order, i Various temperature behaviors that had been observed for different solute systems were also discussed based on the analysis of this work.

Impulszytophotometrische Untersuchungen an synchronisierten Euglena gracilis

The flagellate, Euglena gracilis , which can be cultivated under autotrophic or heterotrophic conditions has been synchronized using light-dark cycles and temperature changes, respectively. Synchronization of autotrophic Euglena cells by light-dark changes was found to be optimal. The kinetics of population growth and synchrony as well as the content of DNA were determined with an impulse cytophotometer. The results suggest that both synchronized Euglena cultures and the method used are suitable for their application as a standardized simple biological test system.

Ecological studies on bacteria in the sea and lake waters polluted with organic substances. III. Growth kinetics of the bacterial populations showing different responses to dissolved organic substances.

By the use of a chemostat the growth kinetics of two different bacterial populations which showed different responses to dissolved organic substances in the natural sea water was studied. The kinetics constants for the growth of Z1-bacteria, grown on a nutrient-rich medium, were: Ks=3.0mgC/l and βm=0.19h-1, and those for the growth of Z/20-bacteria, grown on nutrient-poor medium, were: Ks=1.2mgC/l and βm=0.15-1. Based on these data the relationship between the structure of bacterial community in the sea and the concentration of organic substances in sea water is discussed.

Concepts for systemic treatment of micrometastases.

If total tumor cell kill is a requirement for "cure," as it probably is for at least some tumors, treatment of micrometastases containing less than or equal to 10-6 viable tumor cells is a problem facing all cancer therapists. Metastatic tumor cell foci of less than or equal to 10-6 cells, particularly if widely disseminated, are, in the main, grossly undetectable and are, therefore, the proper targets for the chemotherapist and the immunotherapist. Current knowledge of tumor cell population growth kinetics indicates that the growth fraction (viable cells undergoing active cell replication) is inversely related to population size. Micrometastases should, therefore, be more sensitive to antimetabolite (cell-cycle-specific) anticancer drugs than the larger, grossly apparent, primary tumor from which they were derived. In fact, drug response of the primarytumor may not reliably predict the sensitivity of micrometastases to cell-cycle-specific drugs. In addition, optimal drug treatment scheduling for effective, but noncurative, drugs against clinically recognized tumors may not predict optimal scheduling of the same drugs against micrometastases. This is shown particularly in cell-cycle-specific drugs, since the generation time of tumor cells in small population foci (less than 10-7 cells) is often significantly shorter than in larger population foci (greater than 10-7 cells). Since first-order cell kill kinetics characterizes effective drug kill of tumor cells and the best currently known anticancer drugs have variable but generally limited tumor cell kill potential, drug treatment of likely micrometastases should be started as soon after the end of likely noncurative radiologic or surgical treatment as possible. Experimental data indicating that significantly smaller numbers of viable tumor cells can establish lethal tumors in the presence of radiation-inactivated tumor cells than in their absence suggest that small populations of residual viable tumor cells in radiation-treated tumor sites may be a greater threat to clinical cure than similar sized populations remaining in situ after surgery. Experimental data supporting the above concepts are presented and discussed.

The effect of hypoxia on the growth and radiation response of mammalian cells in culture.

Abstract During prolonged hypoxia, a progressive change occurs in the radiosensitivity of cultured mammalian cells. An attempt was made to determine whether this could be explained on the basis of a progressive change in the life cycle or age distribution of cells during hypoxia. Cell population growth kinetics and the cell life cycle were studied by two conventional methods of analysis. Both indicated an appreciable heterogeneity in the cell populations with regard to the ability of individual cells to negotiate their life cycle during hypoxia. This heterogeneity was confirmed by studying the development of individual microcolonies under hypoxia. From this study, the following conclusions were reached regarding changes which occurred during hypoxia: (1) the growth rate was decreased and the life cycle lengthened; (2) the overall proportion of cells in DNA synthesis decreased with time; (3) on average, a disproportionate lengthening of the G1 phase of the life cycle was implicated; and (4) these changes w...

A multi-unit sampling system and its use in the characterization of ultradian and infradian growth in Tetrahymena.

SYNOPSIS. A multi‐unit automatic sampling device for investigation of microbial growth under a wide variety of conditions is described. The kinetics of asynchronous population growth for batch cultures of Tetrahymena pyriformis (W) at several temperatures show that there are 2 distinct growth phases: an exponential ultradian growth phase that is strongly temperature dependent and a non‐stationary growth phase, the infradian phase, that shows little or no temperature dependence over the range from 15–27 C.