Effects of EGTA on cell surface structures of Corynebacterium glutamicum.

The mycolic acid layer and S-layer of Corynebacterium glutamicum have been considered as permeability barriers against lytic agents. EGTA, a calcium chelator, inhibited C. glutamicum growth at relatively lower concentrations compared with other Gram-positive bacteria. We investigated the effect of EGTA on C. glutamicum cell surface structures. Simultaneous addition of EGTA and lysozyme resulted in cell lysis, whereas addition of these reagents separately had no such effect. Analysis of cell surface proteins showed that CspB, an S-layer protein, was released into the culture media and degraded to several sizes upon EGTA treatment. These findings suggest that EGTA treatment causes release and proteolysis of the CspB protein, resulting in increased cell surface permeability. FE-SEM visualization further confirmed alteration of cell surface structures in EGTA-treated cells. This is the first report suggesting the importance of calcium ions in cell surface integrity of C. glutamicum.

Three-dimensional observation of an immiscible polymer blend subjected to a step electric field under shear flow.

We have investigated the structural change of an immiscible blend consisting of two polymers with equal viscosity subjected to a step electric field under shear flow. During the process, three-dimensional images were successfully acquired with a confocal scanning laser microscope, and at the same time, the transient shear stress was also measured. From the images, the interface tensor was calculated. In a blend of polymers with equal viscosity, the total shear stress may consist of the viscous, interfacial, and electric stresses. An experiment was performed to separate these stresses, and the results are discussed in terms of the interface tensor.

Droplet coalescence process under electric fields in an immiscible polymer blend.

The droplet coalescence process was investigated in immiscible polymer blends when subjected to a step electric field. We present sequential three-dimensional images captured during the process with a confocal scanning laser microscope. Characteristic lengths parallel and perpendicular to the electric field were obtained from the spatial correlation functions of the images. It was found that the droplet growth rate increased with both the electric field and the volume fraction of droplets. A function describing the droplet growth rate was derived from theory using the "hierarchical model" and was found to be in good agreement with the experimental results.

Storage shear modulus of columnar structure formed in an immiscible polymer blend under electric fields.

Oscillatory measurements of a columnar structure were performed, which was formed in an immiscible polymer blend subjected to an electric field. The formation process was observed through a confocal scanning laser microscope and the structure for the measurements was confirmed to be well defined. The storage shear modulus at low frequencies increased with increasing the electric field. A linear relation was found between the storage shear modulus and the square of the electric field. The static modulus calculated on the basis of the Maxwell stress exerted on the interface and interfacial tension was in good agreement with the experimental result.

Response of shear stress to ac electric fields under steady shear flow in a droplet-dispersed phase.

We have measured the response of shear stress to ac electric fields under steady shear flow in the droplet-dispersed phase of an immiscible polymer blend. A characteristic mode was found under steady shear flow, the relaxation frequency of which increased with increasing the shear rate. In the frequency dispersion, a scaling relation derived from dimensional analysis was confirmed to hold. The origin of the mode was investigated on the basis of the Maffettone-Minale (MM) model, in which the droplet shape is described by a second-rank tensor. The frequency dispersion of the response was also calculated using a modified MM model.