Increased Hydrogen Production by Genetic Engineering of Escherichia coli

Escherichia coli is capable of producing hydrogen under anaerobic growth conditions. Formate is converted to hydrogen in the fermenting cell by the formate hydrogenlyase enzyme system. The specific hydrogen yield from glucose was improved by the modification of transcriptional regulators and metabolic enzymes involved in the dissimilation of pyruvate and formate. The engineered E. coli strains ZF1 (ΔfocA; disrupted in a formate transporter gene) and ZF3 (ΔnarL; disrupted in a global transcriptional regulator gene) produced 14.9, and 14.4 µmols of hydrogen/mg of dry cell weight, respectively, compared to 9.8 µmols of hydrogen/mg of dry cell weight generated by wild-type E. coli strain W3110. The molar yield of hydrogen for strain ZF3 was 0.96 mols of hydrogen/mol of glucose, compared to 0.54 mols of hydrogen/mol of glucose for the wild-type E. coli strain. The expression of the global transcriptional regulator protein FNR at levels above natural abundance had a synergistic effect on increasing the hydrogen yield in the ΔfocA genetic background. The modification of global transcriptional regulators to modulate the expression of multiple operons required for the biosynthesis of formate hydrogenlyase represents a practical approach to improve hydrogen production

Mapping Site-Specific Changes that Affect Stability of the NTerminal Domain of Calmodulin

Biophysical tools have been invaluable in formulating therapeutic proteins. These tools characterize protein stability rapidly in a variety of solution conditions, but in general, the techniques lack the ability to discern site-specific information to probe how solution environment acts to stabilize or destabilize the protein. NMR spectroscopy can provide site-specific information about subtle structural changes of a protein under different conditions, enabling one to assess the mechanism of protein stabilization. In this study, NMR was employed to detect structural perturbations at individual residues as a result of altering pH and ionic strength. The N-terminal domain of calmodulin (N-CaM) was used as a model system, and the 1H-15N heteronuclear single quantum coherence (HSQC) experiment was used to investigate effects of pH and ionic strength on individual residues. NMR analysis revealed that different solution conditions affect individual residues differently, even when the amino acid sequence and structure are highly similar. This study shows that addition of NMR to the formulation toolbox has the ability to extend understanding of the relationship between site-specific changes and overall protein stability

Activity of siderophores against drug-resistant Gram-positive and Gram-negative bacteria

Karuna Gokarn,1,2 Ramprasad B Pal1 1Department of Microbiology, Sir Hurkisondas Nurrotumdas Medical Research Society, 2Caius Research Laboratory, St Xavier’s College, Mumbai, India Abstract: Infections by drug-resistant bacteria are life-threatening. As iron is a vital element for the growth of bacteria, iron-chelating agents (siderophores) can be used to arrest their multiplication. Exogenous siderophores – exochelin-MS and deferoxamine-B – were evaluated for their inhibitory activity against methicillin-resistant Staphylococcus aureus and metallo-β-lactamase producers – Pseudomonas aeruginosa and Acinetobacter baumannii – by disc diffusion, micro-broth dilution, and turbidimetric growth assays. The drug-resistant isolates were inhibited by the synergistic activity of siderophores and antibiotics. Minimum inhibitory concentration of exochelin-MS+ampicillin for different isolates was between 0.05 and 0.5 mg/mL. Minimum inhibitory concentration of deferoxamine-B+ampicillin was 1.0 mg/mL and greater. Iron-chelation therapy could provide a complementary approach to overcome drug resistance in pathogenic bacteria. Keywords: iron-chelation, xenosiderophores, exochelin MS, deferoxamine

Solid-gas reactions: effect of solid shape on proposed diffusion model

The diffusion model for gas-solid reactions, proposed by Phadtare and Doraiswamy [9] and applied for the oxidation of zinc sulphide by Gokarn and Doraiswamy [6] for spherical pellets, has been extended to include different geometrical shapes. Model equations have been derived for the long cylinder, right circular cylinder (L = D), infinite cylinder and flat plate. Cylindrical ZnS pellets have been prepared at three different compression pressures, and oxidation carried out at various temperatures for each compression pressure. It has been confirmed that there is a definite shift in the controlling regime and that the "critical temperatures" [i.e. the temperature at which the shift occurs] is dependent on the porosity of the ZnS pellet, shifting to a lower temperature as the porosity is decreased. It has also been observed that the modified kinetic and diffusion models satisfactorily represent the experimental data in the respective zones of control for all the shapes studied. The value of the effective diffusivity obtained by the application of the model to the experimental data for various shapes at a particular temperature has been found to be the same irrespective of the pellet geometry, thus providing further confirmation of the proposed models. In the kinetic regime the activation energy of the reaction has been estimated to be 7.55 kcal/g mole and in the diffusion regime 1.92 kcal/g mole. The Aris approximation for the diffusion length has been found to be applicable to the various geometrical configurations examined, thus proving that this useful approximation, which was so far limited to catalytic reactions, can also be employed for gas-solid reactions

A model for solid-gas reactions

Studies on the oxidation of zinc sulphide spheres suggested kinetic control in the temperature range 600-670°C and diffusion control in the range 740-820°C. In the intermediate range probably both chemical reaction and diffusion are simultaneously operative. In the kinetic regime, experimental data could be fitted to the established Levenspiel model, while in the diffusional regime the model represented by the following equation depicted the data very well: 3θ/AM=x+Bi[1.5-x-1.5(1-x)2/3]. This equation has been derived on the assumption that diffusion of oxygen through the "ash" layer (zinc oxide shell) controls the overall reaction. The effective diffusivity of the reacting and product gases through the ash layer was measured experimentally in a newly developed diffusion cell. The value of the tortuosity parameter (α) thus estimated form an independent set of diffusion experiments and that obtained from kinetic data by using the model represented by the above equation agreed very closely. The external mass transfer coefficient (kg) calculated from the model also need with the values calculated by standard methods. It may therefore be concluded that the above equation (based on the retreating core model) is an adequate representation of the diffusional regime. Similar equtaions can be readily written for other systems starting from Eq. (2) of the text

Analysis of gas-solid reactions: formulation of a general model

A generalised zone reaction model for gas-solid reactions is proposed. It has been shown that the model reduces to the existing models under certain specific conditions which are defined in terms of the width of the reaction zone. Finally criteria are developed for the applicability of the most commonly used shrinking core and homogeneous models