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W R LOCKHART

Publications and source records attributed to W R LOCKHART.

At least 19 recordsLinked to original sources
PubMed1965

ENVIRONMENTAL CONTROL OF CELL COMPOSITION IN ESCHERICHIA COLI.

Wright, D. N. (Iowa State University, Ames), and W. R. Lockhart. Environmental control of cell composition in Escherichia coli. J. Bacteriol. 89:1026-1031. 1965.-Escherichia coli was grown in continuous culture at various rates in a defined medium with either the carbon or the nitrogen source as rate-limiting substrate. Average cell size and the cellular content of ribonucleic acid, protein, and free amino acids varied both with growth rate and with the identity of the limiting nutrient, being greatest at high growth rates, and greater for nitrogen-limited than for carbon-limited populations. Immunoelectrophoresis of cell extracts revealed antigenic components associated uniquely with growth rate, and others associated with the identity of the limiting nutrient on which cells had been grown. Cell composition thus appears to reflect the physiological adjustment of a microbial population to its total environment.

Amino Acids↗
PubMed1965

EFFECTS OF GROWTH RATE AND LIMITING SUBSTRATE ON GLUCOSE METABOLISM IN ESCHERICHIA COLI.

Wright, D. N. (Iowa State University, Ames), and W. R. Lockhart. Effects of growth rate and limiting substrate on glucose metabolism in Escherichia coli. J. Bacteriol. 89:1082-1085. 1965.-Escherichia coli was grown in continuous culture at various rates in a defined medium with either glucose of (NH(4))(2)SO(4) as the rate-limiting substrate. Cellular content of polysaccharide ("glycogen") is greater in cells grown under nitrogen limitation with glucose available in excess, and is greater in rapidly grown than in slowly grown cells. The ability of cells to carry on endogenous respiration, as measured by tetrazolium reduction, can be correlated with their glycogen content. In carbon-limited cultures, the proportion of substrate glucose diverted to glycogen production is least for cells grown slowly, which may reflect greater energy requirements for cell maintenance in such cultures. The activity of glucose-6-phosphate dehydrogenase (indicating function of a C-1 preferential pathway for glucose degradation) is greater in rapidly grown cells, confirming earlier observations in batch cultures. Activity of this enzyme is also greater in nitrogen-limited than in carbon-limited cells, suggesting that there may be catabolic repression of the Embden-Meyerhoff pathway when glucose is available in excess.

Carbohydrate Metabolism↗
PubMed1963

Formation of monothetic groups in quantitative bacterial taxonomy.

Lockhart, W. R. (Department of Bacteriology, Iowa State University, Ames) and P. A. Hartman. Formation of monothetic groups in quantitative bacterial taxonomy. J. Bacteriol. 85:68-77. 1963.-Previous applications of quantitative methods to bacterial classification have resulted in polythetic groupings in which no organism necessarily has all the features characteristic of its group, and no single property is necessarily possessed by every member of a group. Such classifications are not altogether analogous to present taxonomies, and (since the possible groups are not mutually exclusive) hence cannot be evaluated completely by computer methods. A technique is presented for formation of hierarchical monothetic groups in which the criterion for addition of each new member is the possession of an array of properties common to all organisms already in the group. These monothetic relationships among individuals are expressed in terms of cumulative difference, which is linearly related to the taxonomic distance (a function of similarity ratio) of polythetic classifications. Monothetic groupings obtained for 50 representative microorganisms were essentially similar to the polythetic groups evaluated by earlier methods. The necessary computation is suitable for analyzing relationships among large numbers of organisms.

Bacteria↗
PubMed1962

Characteristics and significance of the physiological patterns accompanying growth limitation.

Baarda, I. F. (Iowa State University, Ames) and W. R. Lockhart. Characteristics and significance of the physiological patterns accompanying growth limitation. J. Bacteriol. 84:1085-1093. 1962.-The physiological characteristics of several related strains of Escherichia coli were studied during the transition from exponential growth to stationary phase in defined media with limiting concentrations of the carbon or nitrogen source. The metabolic changes typical of this transition, which often are set in motion before exhaustion of the limiting nutrient has occurred, appear to consist of a series of shifts in the relative emphasis placed on competing reaction sequences leading, respectively, to cell division, protoplasmic synthesis, or cell maintenance. This process of biochemical differentiation has characteristic patterns which are qualitatively distinct for particular limiting nutrients and quantitatively different among strains. Correlation of specific metabolic patterns with the characteristic values of certain growth constants for each strain permits hypotheses concerning the physiological significance of these constants.

Carbon↗
PubMed1961

Relationships between initial nutrient concentration and total growth.

Ecker, R. E. (Iowa State University, Ames), and W. R. Lockhart. Relationships between initial nutrient concentration and total growth. J. Bacteriol. 82:80-84. 1961.-The relationship observed between maximal attainable growth in a microbial population and initial concentration of limiting nutrient depends upon the parameter selected for measurement of growth. A linear relationship is found only when cell mass is the parameter. When population is used as the measure of growth, the relationship is: N(max) = K'C(0) (s), where N(max) is the maximal attainable population, C(0) is the initial concentration of limiting nutrient and K' and s are constants. The use of this expression in demonstrating subtle differences between strains is shown.

Bacteria↗
PubMed1961

Specific effect of limiting nutrient on physiological events during culture growth.

Ecker, R. E. (Iowa State University, Ames), and W. R. Lockhart. Specific effect of limiting nutrient on physiological events during culture growth. J. Bacteriol. 82:511-516. 1961.-In cultures of Escherichia coli strain K12, the sequence of physiological events at the time of growth cessation in populations limited by availability of carbon source (glucose), nitrogen source (ammonium sulfate), and oxygen was observed to differ in several respects. These included differences in the relationship between mass synthesis and cell division, the utilization of nonlimiting nutrients, and the nature of changes in energy metabolism. These observations are discussed with reference to problems involved in the experimental control of variables in growth studies.

Carbon↗