Judith E. Miller

Production of phenylalanine and organic acids by phosphoenolpyruvate carboxylase-deficient mutants ofEscherichia coli

SummaryIsogenic strains ofEscherichia coli were grown aerobically in minimal medium in a 2-liter airlift fermentor to determine whether appc (phosphoenolpyruvate carboxylase) mutation had the effect of directing glucose carbon into phenylalanine synthesis. Two host strains, YMC9 (ppc+) and KB285 (ppc−) were used, either with (Phec) or without (Phe0) a plasmid which determines constitutive phenylalanine production. Carbon consumption and metabolic products were monitored. Phenylalanine production occurred only in strains carrying the Phec plasmid.ppc− strains produced less cell mass and more acetate, pyruvate, and phenylalanine (in the Phec strains) than did isogenicppc+ strains. Lactate and ethanol production were not detected in any of the strains. Phec strains produced less acetate and pyruvate than their Phe0 homologs. Importantly,ppc−/Phec produced at least six times as much phenylalanine (0.32 g phenylalanine/g dry weight cells) asppc+/Phec. Even in this case, however, phenylalanine was produced at ten-fold lower levels than acetate. Thus, although theppc− mutation stimulates phenylalanine production, it also stimulates the production of unwanted by-products such as acetate and pyruvate.

Are Four Heads Better Than One? A Comparison of Cooperative and Traditional Teaching Formats in an Introductory Biology Course

The objective of this experiment was to compare the impact of a cooperative learning format with a traditional lecture-oriented format in the teaching of introductory biology. Differences were found in favor of the cooperative learning format in measures of student satisfaction, the ability to find information on ones own, the acquisition of factual knowledge, and the ability to work with others. The results of this study affirm the viability of using a cooperative learning approach over a traditional lecture format.

The educational developer’s portfolio

The roles and responsibilities described in internationally advertised job opportunities for educational developers reflect the diversity and emerging professionalism of the field. Models adapted from the traditional teaching portfolio are a promising means of articulating these roles and responsibilities, and of defining the nature of the educational development profession.

Effects of immobilization on growth, substrate consumption, β-galactosidase induction, and byproduct formation inEscherichia coli

SummarySome metabolic properties of both suspended and immobilized aerobically and anaerobically growingEscherichia coli cells were investigated. Metabolic activity was found to be substantially different whenE. coli cells were immobilized in alginate. Cells grown immobilized in alginate, and then released from the gel, synthesized 1.6 (aerobic growth) and 4.9 (anaerobic growth) times as much β-galactosidase per cell in response to induction as did suspended cells. Under both aerobic and anaerobic conditions, the cell yield from glycerol for immobilized cells was half that for suspended cells. At specific growth rates that were not significantly different from those of suspended cells, immobilized cells consumed glycerol at twice the rate of suspended cells. Immobilized cells produced elevated quantities of acetate, pyruvate, and lactate. Interpretation of these findings is discussed in terms of the kinetics of energy metabolism and the regulation of inducible protein synthesis inE. coli.

Collegiality in the classroom: The use of Peer Learning Assistants in cooperative learning in introductory biology

Experienced undergraduate students served as Peer Learning Assistants (PLAs) to facilitate group process and dynamics in cooperative learning groups. The use of this model in large classes (150 students) resulted in statistically significant improvements in group performance and satisfaction with the group experience. PLAs defused conflict in groups which were, by their cognitively diverse nature, conflict-prone. Student attitudes about their PLAs and PLA attitudes about the experience were positive. Faculty productivity was substantially enhanced because group dynamics problems rarely landed in the faculty office.

Effect of oxygen supply on metabolism of immobilized and suspended Escherichia coli.

The effect of reduced oxygen supply on the production of a recombinant protein (plasmid-encoded beta-galactosidase) was investigated in Escherichia coli. A novel modified bubble tank reactor was used to provide a direct comparison between immobilized and suspended cells in identical environments except for the immobilization matrix. Decreased oxygen supply led to increased beta-galactosidase synthesis by both immobilized and suspended cells. Immobilized cells produced similar amounts of beta-galactosidase as the suspended cells. Lactose consumption and acetate production, on a per cell basis, were significantly higher in immobilized cells, suggesting that immobilized cells utilized fermentative metabolism. However, a transport analysis of the immobilized cell system showed that immobilized cells were not subject to either external or internal mass transfer gradients.

The problem solving competition: a qualitative method for the assessment of problem solving and teamwork skills

A problem solving competition was used to assess teamwork and communication skills in freshman programs and problem solving in a sophomore chemical engineering curriculum. Invited students were offered compensation of

An investigation of bioreactor performance for the production of recombinant protein in immobilized and suspended Escherichia coli

50 each for an evenings work, plus the chance to win an additional

To Improve the Academy: Resources for Faculty, Instructional, and Organizational Development

50 if their team won the competition. Teams were given limited time and defined access to resources to solve an open-ended problem. Videotaped group work sessions were evaluated by trained raters according to a rubric that varied with the objectives of the assessment. Each groups videotaped oral presentation of their solution was sent to external experts for judging and awarding of prizes. Preliminary results suggest that this method has the potential to provide rich data about how students interact in teams and how they approach open-ended problems. Issues include cost, technical and logistical complexity, audio quality, and subject participation.

Student-Assisted Teaching: A Guide to Faculty-Student Teamwork.

Abstract The performance of packed bed (PBR) and modified bubble tank (MBTR) reactors was compared with respect to recombinant protein (β-galactosidase) production by suspended and immobilized E. coli. The MBTR was superior to the PBR due to easy operation and higher protein production. Gas-liquid mass transfer was not affected by the presence of gel beads, and there were no internal or external oxygen diffusion limitations in either reactor. High substrate concentration, small bead size, low cell densities, and similar values of effective diffusion coefficient of oxygen in water and in alginate may have decreased the internal mass transfer limitations.