High-resolution Video Microscopy Research Articles

Global and local tension measurements in biomimetic skeletal muscle tissues reveals early mechanical homeostasis.

Tension and mechanical properties of muscle tissue are tightly related to proper skeletal muscle function, which makes experimental access to the biomechanics of muscle tissue formation a key requirement to advance our understanding of muscle function and development. Recently developed elastic in vitro culture chambers allow for raising 3D muscle tissue under controlled conditions and to measure global tissue force generation. However, these chambers are inherently incompatible with high-resolution microscopy limiting their usability to global force measurements, and preventing the exploitation of modern fluorescence based investigation methods for live and dynamic measurements. Here, we present a new chamber design pairing global force measurements, quantified from post-deflection, with local tension measurements obtained from elastic hydrogel beads embedded in muscle tissue. High-resolution 3D video microscopy of engineered muscle formation, enabled by the new chamber, shows an early mechanical tissue homeostasis that remains stable in spite of continued myotube maturation.

Motility Analysis of Trypanosomatids.

Motility analysis of microswimmers has long been limited to a few model cell types and broadly restricted by technical challenges of high-resolution in vivo microscopy. Recently, interdisciplinary interest in detailed analysis of the motile behavior of various species has gained momentum. Here we describe a basic protocol for motility analysis of an important, highly diverse group of eukaryotic flagellate microswimmers, using high spatiotemporal resolution videomicroscopy. Further, we provide a special, time-dependent tomographic approach for the proof of rotational locomotion of periodically oscillating microswimmers, using the same data. Taken together, the methods describe part of an integrative approach to generate decisive information on three-dimensional in vivo motility from standard two-dimensional videomicroscopy data.

Direct Observation of Lithium Dendrite Morphology, Propagation, and Reversibility in Garnet Solid Electrolytes Via Operando Video Microscopy

Among the most promising strategies to enable Li metal anodes for next-generation rechargeable batteries is the use of solid-state electrolytes (SSEs). This new generation of batteries with higher gravimetric and volumetric energy density will be critical to the development of a range of applications, perhaps most importantly for electric vehicles (EVs). To date, however, stabilization of the Li metal/SSE interface at high rates of charge has proven challenging in many material systems. The nucleation and propagation of Li filaments has been observed to cause short-circuit in a range of promising SSE materials.1 As fast-charge capability is a key requirement for many applications, but in particular for EVs, overcoming this challenge is critical to enabling the use of Li metal anodes. Limited understanding of the underlying mechanisms by which these Li structures nucleate and propagate within SSE materials has prevented rational design of solutions to the problem.2 In this work, a new operando visualization platform is developed and used to study the propagation of Li filaments within garnet LLZO SSE materials at current densities relevant to fast charge capability. Time-synchronization of voltage traces with high resolution video microscopy reveal new insights into the nature of the dendritic structures, the mechanism by which they propagate, and their reversibility. Post-mortem electron microscopy analysis of specific sites in the operando experiments provides a high resolution, 3D perspective of the structures, and helps to identify pathways for improved performance.

Fast Mechanically Driven Daughter Cell Separation Is Widespread in Actinobacteria.

ABSTRACTDividing cells of the coccoid Gram-positive bacterium Staphylococcus aureus undergo extremely rapid (millisecond) daughter cell separation (DCS) driven by mechanical crack propagation, a strategy that is very distinct from the gradual, enzymatically driven cell wall remodeling process that has been well described in several rod-shaped model bacteria. To determine if other bacteria, especially those in the same phylum (Firmicutes) or with similar coccoid shapes as S. aureus, might use a similar mechanically driven strategy for DCS, we used high-resolution video microscopy to examine cytokinesis in a phylogenetically wide range of species with various cell shapes and sizes. We found that fast mechanically driven DCS is rather rare in the Firmicutes (low G+C Gram positives), observed only in Staphylococcus and its closest coccoid relatives in the Macrococcus genus, and we did not observe this division strategy among the Gram-negative Proteobacteria. In contrast, several members of the high-G+C Gram-positive phylum Actinobacteria (Micrococcus luteus, Brachybacterium faecium, Corynebacterium glutamicum, and Mycobacterium smegmatis) with diverse shapes ranging from coccoid to rod all undergo fast mechanical DCS during cell division. Most intriguingly, similar fast mechanical DCS was also observed during the sporulation of the actinobacterium Streptomyces venezuelae.

Studying Axonal Regeneration by Laser Microsurgery and High-Resolution Videomicroscopy.

Heterogeneous and unpredictable environmental insult, disease, or trauma can affect the integrity and function of neuronal circuits, leading to irreversible neural dysfunction. The peripheral nervous system can robustly regenerate axons after damage to recover the capacity to transmit sensory information to the brain. The mechanisms that allow axonal repair remain incompletely understood. Here we present a preparation in zebrafish that combines laser microsurgery of sensory axons and videomicroscopy of neurons in multicolor transgenic specimens. This simple protocol allows controlled damage of axons and dynamic high-resolution visualization and quantification of repair.

The Nectin-4/Afadin Protein Complex and Intercellular Membrane Pores Contribute to Rapid Spread of Measles Virus in Primary Human Airway Epithelia.

The discovery that measles virus (MV) uses the adherens junction protein nectin-4 as its epithelial receptor provides a new vantage point from which to characterize its rapid spread in the airway epithelium. We show here that in well-differentiated primary cultures of airway epithelial cells from human donors (HAE), MV infectious centers form rapidly and become larger than those of other respiratory pathogens: human respiratory syncytial virus, parainfluenza virus 5, and Sendai virus. While visible syncytia do not form after MV infection of HAE, the cytoplasm of an infected cell suddenly flows into an adjacent cell, as visualized through wild-type MV-expressed cytoplasmic green fluorescent protein (GFP). High-resolution video microscopy documents that GFP flows through openings that form on the lateral surfaces between columnar epithelial cells. To assess the relevance of the protein afadin, which connects nectin-4 to the actin cytoskeleton, we knocked down its mRNA. This resulted in more-limited infectious-center formation. We also generated a nectin-4 mutant without the afadin-binding site in its cytoplasmic tail. This mutant was less effective than wild-type human nectin-4 at promoting MV infection in primary cultures of porcine airway epithelia. Thus, in airway epithelial cells, MV spread requires the nectin-4/afadin complex and is based on cytoplasm transfer between columnar cells. Since the viral membrane fusion apparatus may open the passages that allow cytoplasm transfer, we refer to them as intercellular membrane pores. Virus-induced intercellular pores may contribute to extremely efficient measles contagion by promoting the rapid spread of the virus through the upper respiratory epithelium. Measles virus (MV), while targeted for eradication, still causes about 120,000 deaths per year worldwide. The recent reemergence of measles in insufficiently vaccinated populations in Europe and North America reminds us that measles is extremely contagious, but the processes favoring its spread in the respiratory epithelium remain poorly defined. Here we characterize wild-type MV spread in well-differentiated primary cultures of human airway epithelial cells. We observed that viral infection promotes the flow of cytoplasmic contents from infected to proximal uninfected columnar epithelial cells. Cytoplasm flows through openings that form on the lateral surfaces. Infectious-center growth is facilitated by afadin, a protein connecting the adherens junction and the actin cytoskeleton. The viral fusion apparatus may open intercellular pores, and the cytoskeleton may stabilize them. Rapid homogenization of cytoplasmic contents in epithelial infectious centers may favor rapid spread and contribute to the extremely contagious nature of measles.

Feeding by the newly described heterotrophic dinoflagellate Stoeckeria changwonensis: A comparison with other species in the family Pfiesteriaceae

The feeding ecology of the newly described heterotrophic dinoflagellate Stoeckeria changwonensis was explored. The feeding behavior of S. changwonensis, and the kinds of prey species that it feeds on were investigated with several different types of microscopes and high-resolution video-microscopy. Additionally, the growth and ingestion rates of S. changwonensis as a function of prey concentration for perch (Lateolabrax japonicus) blood cells, the raphidophyte Heterosigma akashiwo, the cryptophytes Rhodomonas salina and Teleaulax sp., and the phototrophic dinoflagellate Amphidinium carterae prey were measured. S. changwonensis feeds on prey through a peduncle, after anchoring the prey by using a tow filament. This type of feeding behavior is similar to that of Stoeckeria algicida, Pfiesteria piscicida, and Luciella masanensis in the family Pfiesteriaceae; however, S. changwonensis feeds on various kinds of prey species different from those of the other heterotrophic dinoflagellates. S. changwonensis ingested perch blood cells and diverse algal species, in particular, the large thecate dinoflagellate Lingulodinium polyedrum which are not eaten by the other peduncle feeders. H. akashiwo and the perch blood cells supported positive growth of S. changwonensis, but R. salina, Teleaulax sp., and A. carterae which support positive growth of P. piscicida and L. masanensis did not support positive growth of S. changwonensis. With increasing mean prey concentration the growth rates for S. changwonensis on H. akashiwo and the perch blood cells increased rapidly and then slowly or became saturated. The maximum growth rates of S. changwonensis on H. akashiwo and the perch blood cells were 0.376 and 0.354d−1, respectively. Further, the maximum ingestion rates of S. changwonensis on H. akashiwo and the perch blood cells were 0.35ngCpredator−1d−1 (3.5cellspredator−1d−1) and 0.27ngCpredator−1d−1 (29cellspredator−1d−1), respectively. These maximum growth and ingestion rates of S. changwonensis on H. akashiwo, the perch blood cells, R. salina, Teleaulax sp., and A. carterae differed considerably from those of S. algicida, P. piscicida, and L. masanensis on the same prey species. Thus, the feeding behavior of S. changwonensis may differ from that of other species in the family Pfiesteriaceae.

Time-lapse video microscopy and image analysis of adherence and growth patterns of Candida albicans strains

Digital image analysis of high time resolution video microscopy was used to investigate hyphal growth dynamics in different Candida albicans strains. The effects of the quorum sensing molecules tyrosol and farnesol, the deletion of the fungus specific protein phosphatase Z1 CaPPZ1), and the hypha-specific cyclin (HGC1) genes were analyzed by this method. Our system monitored cell growth in a CO2 incubator under near-physiological conditions and measured three major parameters under the following stringent conditions: (a) the time of yeast cell adherence, (b) the time of hyphal outgrowth, and (c) the rate of hyphal growth. This method showed that hyphal extension of wild-type SC5314 cells was accelerated by tyrosol and inhibited by farnesol. Hyphal growth rate was moderately lower in cappz1 and strongly reduced in hgc1 mutants. In addition, tyrosol treatment caused a firm adherence, while farnesol treatment and hgc1 mutation prevented the adherence of yeast cells to the surface of the culture flask. Transition from yeast-to-hyphal state was faster after tyrosol treatment, while it was reduced in farnesol-treated cells as well as in the cappz1 and hgc1 mutants. Our data confirm the notion that the attachment of yeast cells, the yeast-to-hyphal transition, and hyphal growth rate are closely related processes. Time-lapse video microscopy combined with image analysis offers a convenient and reliable method of testing chemicals, including potential drug candidates, and genetic manipulations on the dynamic morphological changes in C. albicans strains.

Concentration landscape generators for shear free dynamic chemical stimulation

In this paper we first introduce a novel fabrication process, which allows for easy integration of thin track-etched nanoporous membranes, within 2D or 3D microchannel networks. In these networks, soluble chemical compounds can diffuse out of the channels through well-defined and spatially organized microfabricated porous openings. Interestingly, multiple micron-scale porous areas can be integrated in the same device and each of these areas can be connected to a different microfluidic channel and reservoir. We then present and characterize several membrane-based microdevices and their use for the generation of stable diffusible concentration gradients and complex dynamic chemical landscapes under shear free conditions. We also demonstrate how a simple flow-focusing geometry can be used to generate "on-demand" concentration profiles. In turn, these devices should provide an ideal experimental framework for high throughput cell-based assays: long term high-resolution video microscopy experiments can be performed, under multiple spatially and temporally controlled chemical conditions, with simple protocols and in a cell-friendly environment.

Feeding by the Newly Described, Nematocyst‐Bearing Heterotrophic Dinoflagellate Gyrodiniellum shiwhaense

We explored the feeding ecology of the newly described, nematocyst-bearing heterotrophic dinoflagellate Gyrodiniellum shiwhaense (GenBank accession number=FR720082). Using several different types of microscopes and high-resolution video-microscopy, we investigated feeding behavior and types of prey species that G. shiwhaense feeds upon. Additionally, we measured its growth and ingestion rates on its optimal algal prey, the cryptophyte Teleaulax sp. and the dinoflagellate Amphidinium carterae, as a function of prey concentration. These rates were measured for other edible prey at single prey concentrations at which the growth and ingestion rates of G. shiwhaense were saturated. After anchoring the prey with a tow filament, G. shiwhaense fed using a peduncle, ingesting small algal species with equivalent spherical diameters (ESDs) of <13 μm. However, it did not feed on larger algal species that had ESDs≥13 μm or the small diatom Skeletonema costatum. The specific growth rates for G. shiwhaense feeding upon Teleaulax sp. and A. carterae increased rapidly with increasing mean prey concentration before saturating at concentrations of ca. 180-430 ng C/ml. The maximum specific growth rate of G. shiwhaense on Teleaulax sp. and A. carterae were 1.05 and 0.82/d, respectively. However, Heterosigma akashiwo did not support positive growth of G. shiwhaense. The maximum ingestion rates of G. shiwhaense on Teleaulax sp. and A. carterae were 0.35 and 0.54 ng C/grazer/d, respectively. The calculated grazing coefficients attributable to G. shiwhaense on co-occurring cryptophytes and Amphidinium spp. were 0.01-1.87/d and 0.08-2.60/d, respectively. Our results suggest that G. shiwhaense can have a considerable grazing impact on algal populations.

AUTOMATIC ESTIMATION OF SIZE PARAMETERS USING VERIFIED COMPUTERIZED STEREOANALYSIS

State-of-the-art computerized stereology systems combine high-resolution video microscopy and hardwaresoftware integration with stereological methods to assist users in quantifying multidimensional parameters of importance to biomedical research, including volume, surface area, length, number, their variation and spatial distribution. The requirement for constant interactions between a trained, non-expert user and the targeted features of interest currently limits the throughput efficiency of these systems. To address this issue we developed a novel approach for automatic stereological analysis of 2-D images, Verified Computerized Stereoanalysis (VCS). The VCS approach minimizes the need for user interactions with high contrast [high signal-to-noise ratio (S:N)] biological objects of interest. Performance testing of the VCS approach confirmed dramatic increases in the efficiency of total object volume (size) estimation, without a loss of accuracy or precision compared to conventional computerized stereology. The broad application of high efficiency VCS to high-contrast biological objects on tissue sections could reduce labor costs, enhance hypothesis testing, and accelerate the progress of biomedical research focused on improvements in health and the management of disease.

Mixotrophy in Red Tide Algae Raphidophytes1

Marine raphidophytes are common red tide organisms that are distributed worldwide. They are known to be harmful to other plankton and fish and have often caused large-scale fish mortality in many countries. Thus, the population dynamics of raphidophytes is a critical concern for scientists, the aquaculture industry, and government officers from many countries. Raphidophyte growth and mortality should be investigated to understand bloom dynamics. Raphidophytes were thought to be exclusively autotrophic organisms. However, several recent studies have revealed that raphidophytes are able to feed on heterotrophic and autotrophic bacteria, i.e. raphidophytes are mixotrophic algae. Further, high-resolution video microscopy has revealed the mechanism by which raphidophytes feed on bacteria, which involves capturing prey cells in the mucus excreted by mucocysts and engulfing the cells through mucocysts. These discoveries may influence the conventional view on both raphidophyte bloom dynamics and plankton energy flow and carbon cycling. In the present study, I review prey, feeding mechanisms, and ingestion rates of mixotrophic marine raphidophytes. In addition, I examine the ecological significance of raphidophyte mixotrophy.

Feeding by the Newly Described Mixotrophic Dinoflagellate Paragymnodinium shiwhaense: Feeding Mechanism, Prey Species, and Effect of Prey Concentration

To investigate the feeding by the newly described mixotrophic dinoflagellate Paragymnodinium shiwhaense (GenBank accession number=AM408889), we explored the feeding process and the kinds of prey species that P. shiwhaense is able to feed on using several different types of microscopes, including a transmission electron microscope and high-resolution video-microscopy. In addition, we measured the growth and ingestion rates of P. shiwhaense on its optimal algal prey Amphidinium carterae as a function of prey concentration. We also measured these parameters for edible prey at a single concentration at which the growth and ingestion rates of P. shiwhaense on A. carterae were saturated. Paragymnodinium shiwhaense feed on algal prey using a peduncle after anchoring the prey by a tow filament. Among the algal prey offered, P. shiwhaense ingested small algal species that had equivalent spherical diameters (ESDs) < or =11 microm (e.g. the prymnesiophyte Isochrysis galbana, the cryptophytes Teleaulax sp. and Rhodomonas salina, the raphidophyte Heterosigma akashiwo, and the dinoflagellates Heterocapsa rotundata and A. carterae). However, it did not feed on larger algal species that had ESDs > or =12 microm (e.g. the dinoflagellates Prorocentrum minimum, Heterocapsa triquetra, Scrippsiella trochoidea, Alexandrium tamarense, Prorocentrum micans, Gymnodinium catenatum, Akashiwo sanguinea, and Lingulodinium polyedrum) or the small diatom Skeletonema costatum. The specific growth rates for P. shiwhaense feeding upon A. carterae increased rapidly with increasing mean prey concentration before saturating at concentrations of ca. 350 ng C/ml (5,000 cells/ml). The maximum specific growth rate (i.e. mixotrophic growth) of P. shiwhaense on A. carterae was 1.097/d at 20 degrees C under a 14:10 h light-dark cycle of 20 microE/m(2)/s, while its growth rate (i.e. phototrophic growth) under the same light conditions without added prey was -0.224/d. The maximum ingestion and clearance rates of P. shiwhaense on A. carterae were 0.38 ng C/grazer/d (5.4 cells/grazer/d) and 0.7 microl/grazer/h, respectively. The calculated grazing coefficients for P. shiwhaense on co-occurring Amphidinium spp. was up to 0.07/h (i.e. 6.7% of the population of Amphidinium spp. was removed by P. shiwhaense populations in 1 h). The results of the present study suggest that P. shiwhaense can have a considerable grazing impact on algal populations.

Feeding by raphidophytes on the cyanobacterium Synechococcus sp.

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 58:181-195 (2010) - DOI: https://doi.org/10.3354/ame01354 Feeding by raphidophytes on the cyanobacterium Synechococcus sp. Hae Jin Jeong1,*, Kyeong Ah Seong2, Nam Seon Kang1, Yeong Du Yoo1, Seung Won Nam3, Jae Yeon Park4, Woongghi Shin5, Patricia M. Glibert6, Desmond Johns6 1School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Republic of Korea 2Saemankeum Environmental Research Center, Kunsan National University, Kunsan 573-701, Republic of Korea 3Division of Electron Microscopic Research, Korea Basic Science Institute, 113 Gwahangno, Yuseong-gu, Daejeon 305-333, Republic of Korea 4Environment Energy Resource Institute, Advanced Institute of Convergence Technology, Suwon 443-270, Republic of Korea 5Department of Biology, Chungnam National University, Daejeon 305-764, Republic of Korea 6University of Maryland Center for Environmental Science, Horn Point Laboratory, PO Box 775, Cambridge, Maryland 21613, USA *Email: hjjeong@snu.ac.kr ABSTRACT: We investigated feeding by the raphidophytes Chattonella ovata, C. subsalsa, Fibrocapsa japonica, and Heterosigma akashiwo on the cyanobacterium Synechococcus sp. To explore whether each species is able to feed on Synechococcus sp., we carefully observed inside target grazer cells using an epifluorescence microscope and tranbsmission electron microscope (TEM). We also explored the feeding behaviors of C. ovata and H. akashiwo on Synechococcus using high-resolution video microscopy. In addition, we measured ingestion rates of C. ovata, C. subsalsa and H. akashiwo on Synechococcus sp. as a function of prey concentration. We calculated grazing coefficients by combining the field data on abundances of H. akashiwo and co-occurring Synechococcus spp. with laboratory data on ingestion rates. Both C. ovata and H. akashiwo were able to ingest single Synechococcus cells. However, neither TEM nor video microscopy showed any Synechococcus cells inside or ingested by F. japonica. One to two ingested Synechococcus cells inside the protoplasm of F. japonica cells were very rarely observed. C. ovata and H. akashiwo engulfed a single Synechococcus cell captured by the mucus excreted from mucocysts. The ingestion rates of C. ovata, C. subsalsa, or H. akashiwo on Synechococcus increased continuously with increasing prey concentration at prey concentrations ≤4 × 106 to 5.5 × 106 cells ml–1. At a given prey concentration, the highest ingestion rates of the raphidophytes on Synechococcus were 18.6 cells raphidophyte–1 h–1 for C. ovata, 20.5 cells raphidophyte–1 h–1 for C. subsalsa, and 3.9 cells raphidophyte–1 h–1 for H. akashiwo. The calculated grazing coefficients attributable to H. akashiwo on co-occurring Synechococcus spp. were up to 1.24 d–1. The results of the present study suggest that raphidophytes sometimes have a considerable grazing impact on populations of Synechococcus. KEY WORDS: Chattonella spp. · Fibrocapsa japonica · Graze · Heterosigma akashiwo · Harmful algal bloom · HAB · Ingestion · Red tide Full text in pdf format Supplementary material PreviousNextCite this article as: Jeong HJ, Seong KA, Kang NS, Yoo YD and others (2010) Feeding by raphidophytes on the cyanobacterium Synechococcus sp.. Aquat Microb Ecol 58:181-195. https://doi.org/10.3354/ame01354Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 58, No. 2. Online publication date: January 07, 2010 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2010 Inter-Research.

A coculture assay to visualize and monitor interactions between migrating glioma cells and nerve fibers

Glioma-cell migration is usually assessed in dissociated cell cultures, spheroid cultures, acute brain slices and intracranial implantation models. However, the interactions between migrating glioma cells and neuronal tracts remain poorly understood. We describe here a protocol for the coculture of glioma cells with myelinated axons in vitro. Unlike other methods, this protocol allows the creation of in vitro conditions that largely mimic the complex in vivo environment. First, long retinal axons from embryonic chicken are formed in an organotypic culture. Glioma cells are then positioned in the vicinity of the explants to allow them to contact the axons, interact with them and eventually migrate along them. High-resolution video microscopy and confocal microscopy can be used to monitor the migratory behavior. This protocol, which takes about 5 days to complete, could be applied to different types of tumor cells that interact with neurites, and is suitable for pharmacological and genetic approaches aimed at elucidating mechanisms underlying tumor migration.

A novel view on stem cell development: analysing the shape of cellular genealogies

The analysis of individual cell fates within a population of stem and progenitor cells is still a major experimental challenge in stem cell biology. However, new monitoring techniques, such as high-resolution time-lapse video microscopy, facilitate tracking and quantitative analysis of single cells and their progeny. Information on cellular development, divisional history and differentiation are naturally comprised into a pedigree-like structure, denoted as cellular genealogy. To extract reliable information concerning effecting variables and control mechanisms underlying cell fate decisions, it is necessary to analyse a large number of cellular genealogies. Here, we propose a set of statistical measures that are specifically tailored for the analysis of cellular genealogies. These measures address the degree and symmetry of cellular expansion, as well as occurrence and correlation of characteristic events such as cell death. Furthermore, we discuss two different methods for reconstruction of lineage fate decisions and show their impact on the interpretation of asymmetric developments. In order to illustrate these techniques, and to circumvent the present shortage of available experimental data, we obtain cellular genealogies from a single-cell-based mathematical model of haematopoietic stem cell organization. Based on statistical analysis of cellular genealogies, we conclude that effects of external variables, such as growth conditions, are imprinted in their topology. Moreover, we demonstrate that it is essential to analyse timing of cell fate-specific changes and of occurrence of cell death events in the divisional context in order to understand the mechanisms of lineage commitment.

Mitochondrial movement is random and increased by hyposalinity in coelomocytes from an estuarine worm

Mitochondria typically move non‐randomly due to attachment to cytoskeletal components. We investigated whether variation in ambient salinity affects mitochondrial movement in coelomocytes (nucleated “blood cells”) from the estuarine annelid Glycera dibranchiata using high‐resolution fluorescence video microscopy of live coelomocytes labeled with MitoTracker Green FM. Cells were exposed to normal seawater (1000 mOsm/L) or seawater diluted to 750, 500 and 250 mOsm/L (all with 10 mM HEPES and 0.1% glucose). Cell area and mitochondrial motion were analyzed in 100 cells and 400 mitochondria in a split plot, fully nested design (5 mitochondria x 5 cells x 4 worms x 4 dilutions). Surprisingly, mitochondrial movement at 1000 mOsm/L was continuous and random, characteristic of Brownian motion. Decreasing osmolarity proportionally increased the cell volume (P&lt;0.001), as expected, but also increased the length of each mitochondrial track (P&lt;0.0001) and the average total displacement (P&lt;0.001), with mitochondrial movement at 250 mOsm/L being 2.8‐fold greater than at 1000 mOsm/L. Furthermore, the change in the mitochondrial diffusion coefficient was 3‐fold greater than that predicted by the direct effect of salinity on water viscosity. We propose that changes in the composition of intracellular organic osmolytes associated with salinity adaptation substantially affect the motion of these organelles.

A study of electric field enhanced ultrafiltration of synthetic fruit juice and optical quantification of gel deposition

The effects of externally applied electric field during cross-flow ultrafiltration of synthetic juice (mixture of sucrose and pectin) are studied and the gel thicknesses are measured optically. The introduction of the electric field is found to be quite effective in enhancing the permeate flux due to the electrophoresis of the gel forming pectin molecules away from the membrane surface. A model based on gel layer theory is proposed and numerically solved to quantify the flux and growth of the gel layer thickness. The gel layer thickness is also measured with high-resolution video microscopy and successfully compared with results from the numerical solution of the model under various operating conditions.

The real-time, high-resolution x-ray video microscopy of solidification in aluminum alloys

The directional solidification of thin alloy sheets in a Bridgman furnace has been studied by x-radiography using high-brilliance synchrotron x-radiation in combination with a low-noise, fast-readout camera. Spatial resolutions down to 1.5 μm and a temporal resolution of about 0.15 s have permitted real-time video microscopy of microstructural evolution during columnar and equiaxed dendrite growth and eutectic and monotectic growth. The technique has also allowed for direct observations of important solidification phenomena such as dendrite fragmentation and porosity formation, primarily in aluminium alloys. As a result, insights have been gained into mechanisms of dendrite fragmentation, criteria for dendrite tip kinetics and interface stability during transient growth, and microstructure formation mechanisms during monotectic solidification. The results are expected to be important for validation of dendrite growth models. This paper presents a review of the technique as well as examples of images obtained during solidification of aluminum alloys.

High Motility Reduces Grazing Mortality of Planktonic Bacteria

We tested the impact of bacterial swimming speed on the survival of planktonic bacteria in the presence of protozoan grazers. Grazing experiments with three common bacterivorous nanoflagellates revealed low clearance rates for highly motile bacteria. High-resolution video microscopy demonstrated that the number of predator-prey contacts increased with bacterial swimming speed, but ingestion rates dropped at speeds of >25 microm s(-1) as a result of handling problems with highly motile cells. Comparative studies of a moderately motile strain (<25 microm s(-1)) and a highly motile strain (>45 microm s(-1)) further revealed changes in the bacterial swimming speed distribution due to speed-selective flagellate grazing. Better long-term survival of the highly motile strain was indicated by fourfold-higher bacterial numbers in the presence of grazing compared to the moderately motile strain. Putative constraints of maintaining high swimming speeds were tested at high growth rates and under starvation with the following results: (i) for two out of three strains increased growth rate resulted in larger and slower bacterial cells, and (ii) starved cells became smaller but maintained their swimming speeds. Combined data sets for bacterial swimming speed and cell size revealed highest grazing losses for moderately motile bacteria with a cell size between 0.2 and 0.4 microm(3). Grazing mortality was lowest for cells of >0.5 microm(3) and small, highly motile bacteria. Survival efficiencies of >95% for the ultramicrobacterial isolate CP-1 (< or =0.1 microm(3), >50 microm s(-1)) illustrated the combined protective action of small cell size and high motility. Our findings suggest that motility has an important adaptive function in the survival of planktonic bacteria during protozoan grazing.