Michelle K. Bothwell

Physicochemical properties of pretreated poplar feedstocks during simultaneous saccharification and fermentation

Physicochemical properties of native and dilute acid pretreated (0.6% H2SO4, 10 min, and either 170°C or 180°C) poplar were investigated before and during simultaneous saccharification and fermentation (SSF). SSF duration was 5 days and employed Trichoderma reesei cellulases and Saccharomyces cerevisiae fermentation. Chemical composition (glucan, xylan, lignin), enzyme-accessible surface area (based on solute exclusion), crystallinity index, particle size distribution, particle shape, and enzyme adsorption (cellulase, β-glucosidase) were compared to cellulose conversion. Cellulose conversion varied from 8% for native poplar to 78% for the 180°C-pretreated poplar. The physicochemical properties of native poplar changed little during SSF. In contrast, the physicochemical properties of the 180°C-pretreated feedstock changed markedly. Enzyme-accessible surface area and β-glucosidase adsorption increased by 83% and 65%, respectively, as cellulose was removed from the feedstock. Crystallinity index and particle size (large fraction) decreased by 65% and 93%, respectively. Cellulase adsorption per unit weight increased initially (+45%) followed by a slight decrease (−13%). The same trends were observed, although to a lesser extent, for 170°C-pretreated feedstock.

Adsorption of Trichoderma reesei CBHI cellulase on silanized silica.

Adsorption kinetics and surfactant-mediated elution of Trichoderma reesei CBHI cellulase were recorded in situ, at hydrophobic, silanized silica. Experiments were performed at different solution concentrations, ranging from 0.001 to 0.98 mg/mL. Adsorbed enzyme was partially elutable upon rinsing, with the amount of adsorbed mass remaining being highest at intermediate concentrations. In addition, the resistance to elution with buffer was generally lower at higher concentrations, and the resistance to elution with surfactant was generally lower at intermediate concentrations. These observations are tentatively explained with reference to a mechanism allowing for adsorption of associated monomers of CBHI as well as free monomers.

Adsorption of Thermomonospora fusca E5 and Trichoderma reesei cellobiohydrolase I cellulases on synthetic surfaces

The interfacial behavior of Thermomonospora fusca E5 and Trichoderma reesei cellobiohydrolase I (CBHI) cellulases were studied at synthetic surfaces. For this purpose, colloidal silica and polystyrene particles were used to prepare cellulase-particle suspensions that could be analyzed by solution-phase techniques. Circular dichroism spectroscopy of each cellulase, alone as well as in suspension with silica, was used to determine whether structural changes occurred on adsorption. Changes in spectra were observed for CBHI, but not for E5. Gel-permeation chromatography of the cellulase-particle suspensions showed that neither cellulase binds to silica, suggesting that changes in spectra for CBHI were a result of solution-phase phenomena. Microfiltration of cellulase-polystyrene suspensions showed that both cellulases bind to polystyrene. However, circular dichroism experiments with polysterene proved unworkable, owing to excessive light absorption by the polystyrene. Adsorption kinetics of each cellulase were recorded, in situ, at hydrophilic and silanized, hydrophobic silica surfaces using ellipsometry. Ellipsometric data recorded for each cellulase at hydrophilic silica showed insignificant adsorption. Binding did occur between each cellulase and silanized silica, most likely mediated through hydrophobic associations. Adsorption in this case was irreversible to dilution.

STEM Women Faculty Struggling for Recognition and Advancement in a “Men’s Club” Culture

Despite having made a number of positive steps to advance diversity and provide support for women scientist in the past ten years, STEM research institutions continue to be an environment where women faculty face a kind of “patriarchal DNA” that treats women scientists as subordinate to men. An environment continues to exist where women faculty often feel unwelcome, and unsatisfied with the rate of their accomplishments. At the time of promotion and tenure women can feel a sense of betrayal as their work is evaluated as being “less than” the work of men. To be successful in a derisive environment, many STEM women faculty report that they have developed coping strategies to adapt to a culture that often excludes them from occupying senior leadership roles, diminishes their accomplishments, and makes them feel remorseful for trying to find a work–life balance.

Special session - increasing awareness of issues of poverty, environmental degradation and war within the engineering classroom: A course modules approach

The goals of the proposed special session are the following: (1) Describe ongoing efforts at various institutions which attempt to integrate the issues of poverty, environmental degradation and war into existing engineering courses; (2) Describe process(es) used in developing course modules; (3) Provide an interactive, experiential process whereby the session participants will begin to develop their own course modules for use in their respective courses; (4) Further develop a community interested in increasing awareness of issues of poverty, environmental degradation and war within engineering education and the engineering profession; and (5) Explore options for establishing closer ties between the course modules and real-world community agencies/organizations.