Spotted fever group (SFG) rickettsiae are obligate intracellular prokaryotes that include tick-borne pathogens of vertebrates as well as nonpathogenic organisms living in symbiotic association with their tick hosts. We investigated the ability of SFG rickettsiae to move between and within host cells using tick cell culture and a SFG rickettsial isolate from a lone star tick (Amblyomma americanum) collected in Missouri. The isolate (MOAa), which is closely related to Rickettsia montana, grew in cell lines from the ticks Ixodes scapularis and Rhipicephalus appendiculatus. Transmission electron microscopy demonstrated that immediately following entry into tick cells, rickettsiae escaped from the host cell membrane, and intracellular rickettsiae came to lie in direct contact with host-cell cytoplasm. There was evidence of damage to the endoplasmic reticulum membrane which was broken down into vesicular structures. When rickettsiae exited host cells, host membrane stretched around them but was lost before re-entry. Use of a fluorescein-tagged monoclonal antibody to rickettsial outer membrane protein B and rhodamine-labeled phalloidin demonstrated association of actin tails with rickettsiae and suggested that SFG rickettsiae utilized host cytoskeletal components for movement. During early stages of infection, when cells harbored only one or a few organisms, “comet tails” of F-actin formed on one end of rickettsial cells, presumably pushing them ahead. Actin tails were not seen during later stages of infection when tick cells became completely filled with rickettsiae.

Particle size distributions obtained from a thin section are usually a skewed version of the true distribution. A previous method for determining the parent distribution was questionable because negative particle frequencies could be obtained. Here, we describe a method of determining parent distributions of spherical particles using a model with adjustable parameters. Our calculated distributions are somewhat broader than the distributions obtained with previous methods, but the average particle sizes are nearly identical. The newly developed model is applicable to any type of transmission microscopy.

A method for preparing a cross-section sample from a free-standing thin-film coupon suitable for transmission electron microscopy analysis has been successfully developed. The free-standing coupon presented a significant challenge for the preparation of a cross-section sample. A stack consisting of a silicon wafer, thin-film coupon, and glass coverslip was epoxied together, providing both support for thin film and enough surface area to handle the specimen during the sample preparation procedure. The tripod polisher wedge technique was used to thin the cross-section sample to 2 to 5 μm in thickness. This produced a sample with the required structural integrity. Final thinning was accomplished using an ion mill. This technique showed no artifacts introduced from the sample preparation procedure.

The quantity and spatial distribution of calcium bound to myofilaments is of considerable interest to physiologists studying the regulation of contraction in striated muscle, but few techniques allow these distributions to be directly measured. Methods are described here by which such data can be derived from electron probe X-ray microanalysis (EPXMA) images. Combination of data from multiple half sarcomeres improves the signal-to-noise level and allows assessment of variation between half sarcomeres. Profiles of calcium counts, calcium counts normalized to local bremstrahlung counts, and calcium counts normalized to the average bremstrahlung counts for the entire half sarcomere provide differing but complementary information. Such data help to identify and characterize spatial variations in Ca binding to regulatory proteins in muscle.

The kinetics of a thin-film, solid-state reaction were investigated in the spinel-forming oxide system Fe2O3/MgO. In this study, epitactic thin films of Fe2O3 (α, or corundum, structure) were deposited on (001)-oriented MgO using pulsed-laser deposition (PLD). The resulting diffusion couples were then reacted at elevated temperatures in air to induce the reaction between the thin-film and bulk substrate to form the spinel, MgFe2O4. Both the as-deposited and reacted diffusion couples were characterized using low-voltage scanning and transmission electron microscopy. These techniques allow the kinetics of the reaction and the structural properties of the spinel to be investigated.

This study describes the use of transmission electron holography to determine the mean inner potential of polystyrene. Spherical nanoparticles of amorphous polystyrene are studied so that the effect of specimen thickness on the phase shift of an incident electron wave can be separated from the intrinsic refractive properties of the specimen. A recursive four-parameter χ-squared minimization routine is developed to determine the sphere center, radius, and mean inner potential (Φ0) at each pixel in the phase image. Because of the large number of pixels involved, the statistics associated with determining a single Φ0 value characteristic of a given sphere are quite good. Simulated holograms show that the holographic reconstruction procedure and the χ-squared analysis method are robust. Averaging the Φ0 data derived from ten phase images from ten different polystyrene spheres gives a value of Φ0PS = 8.5 V (σ) = 0.7 V). Specimen charging and electron-beam damage, if present, affect the measurement at a level below the current precision of the experiment.

The use of Pt to mark the initial location of heterophase boundaries in solid-state reactions was extended to investigate the motion of interfaces during a thin-film solid-state reaction between In2O3 and MgO in the presence of an electric field. The Pt markers were prepared by sputtering a thin Pt film onto a single-crystal substrate. The resulting multilayer was then heated prior to thin-film deposition to de-wet the Pt film and thus form an array of small, isolated particles. These particles serve as fine-scale markers for tracking the motion of interfaces. However, there are certain situations in which the markers can move with the interface.

Fluorescence Microscopy and Fluorescence Probes, edited by Jan Slavik, 1996. Plenum Press, New York and London. 306 pages. (hardback, $95)

This volume is a compilation of abstracts of papers presented at the Fluorescence Microscopy and Fluorescence Probes Conference held in Prague in June 1995. This conference was one of the first tangible results of the end of the Cold War in the field of microscopy. As such, it attracted a great many of those who constitute the vanguard of progress in the field of fluorescence microscopy, on both sides of the old East-West divide. About one-third of the 127 contributors were from the West.

In this issue is an article about Albert Pre-bus, one of the pioneers in electron microscopy who recently passed away. John Watson has written much more than an obituary for this man, almost a biography. This kind of article enriches our understanding of the roots of microscopy and commemorates the contributions of an individual very important to the development of microscopy. It is my hope that this will be the first of such articles about individuals who've made major contributions to technical developments or disciplines upon which our exploration and understanding of structural and/or chemical characterization rests. If you are interested in writing an a-rticle about such an historical figure please contact me or if you have a suggestion of a name of someone you think would be desirable to have profiled, please send me that suggestion as well.

One of the two men who first brought the electron microscope to the North American continent in 1938 died on December 16, 1997, at his home in Columbus, Ohio. This description of Dr. Albert Prebus' life is not so much an obituary as it is a recognition of a quiet, modest, unassuming scientist, whose pioneering work in electron microscopy contributed directly to the great explosion of scientific knowledge, which has been characteristic of the last half of the twentieth century.

This list contains brief descriptions of each of the positions known to be open in Microscopy Society of America (MSA) Placement Office files as of January 1, 1998. Potential employers are urged to use the Placement Office as widely as possible to advertise their needs to MSA members. Likewise, MSA members who are seeking employment in microscopy are urged to register with the Office to receive data on open positions periodically.

E-mail messages regarding Microscopy and Microanalysis.

Following is a list of microscopy-related meetings and courses. The editors would greatly appreciate input to this list via the electronic submission form found in the MSA World-Wide Web page at http://www.msa.microscopy.com/. We will gladly add hypertext links to the notice on the Web and insert a listing of the meeting in the next issue of the Journal. Send comments and questions to Barbara Reine, [email protected] or Nestor Zaluzec, [email protected].