Dictyostelium discoideum fruiting bodies observed by scanning electron microscopy.

The fruiting bodies of Dictyostelium discoideum, fixed in a vapor of 25% glutaraldehyde, were observed by scanning electron microscopy. The surface of the basal disk had rootlike ripples, sometimes with concentric rings of riblike striations at its periphery. The surface of the stalk had pleated and twisted ridges along its entire length, but no lateral projections. The spores were randomly orientated and had a crinkled surface. The surface of the lower part of the papilla had flattened ridges running horizontally. A slime coat remained in the region of transition between the stalk and sporangium, but not on the spores.     

Improved methods of isolation and purification of myxobacteria and development of fruiting body formation of two strains

By using baiting techniques and different purification methods, a high number of myxobacterial strains have been isolated as pure cultures from soil of different regions of China. Because myxobacterial cells do not disperse easily in liquid media, a medium containing an enzymatic hydrolysate of casein (CEH) medium have been used for purification and purity tests combined in a single step. The key method, in which isolates are reintroduced to sterile rabbit dung to induce fruiting bodies formation, facilitates purification of myxobacteria. Sterile rabbit dung pellets are used to mimic the natural growth substance of these organisms which has the advantage that characteristic fruiting bodies emerge, which is a key characteristics in the taxonomy of myxobacteria. In this study, the optimum program of isolation and purification of some myxobacteria strains has been established which will facilitate screening programs. Moreover, the development of fruiting body formation of strain BD20 (Chondromyces) and strain BD54 (Cystobacter) have been recorded in this study.     

Scanning electron microscopy of vaginal colonization.

Changes in the appearance of the vaginal epithelium of rats during the estrous cycle were seen by scanning electron microscopy. Bacterial colonization of this tissue appeared to be influenced by these changes.     

Scanning electron microscopy of the vitreous body in the rat eye

Summary The vitreous body of the rat eye was studied by scanning electron microscopy. The freeze-dried specimens were either unfixed, freshly frozen or fixed and rinsed before being frozen.The vitreous body is surrounded by a coat of intercellular material covering a thin sheath of chiefly parallel fibers. The latter forms the base for a regularly organized three-dimensional network of fibers. The interfibrillar spaces are filled with ground substance and also contain a few cells. The shape of the cells varies from bipolar to polyhedronal. Their interconnected processes are usually undivided. The functional importance of this complex regular organization of the fibers and cells in the vitreous body is stressed.Supported by grants from H. Jeanssons Stiftelse and the Swedish Medical Research Council (B70-12X-2534-02).I would like to thank the Swedish Silicate Research Institute, Göteborg, for using their scanning electron microscope and Miss M. Persson for skilful technical assistance.     

Adenylate energy charge during fruiting body formation by Myxococcus xanthus.

The adenylate energy charge of developing Myxococcus xanthus cells was measured. The energy charge of vegetative cells (0.81) does not change significantly during the course of fruiting body formation. Furthermore, myxospores, which are resistant, resting cells present in the fruiting body, have a relatively high energy charge (0.73).     

Developmentally induced autolysis during fruiting body formation by Myxococcus xanthus.

The developmental events during fruiting body construction by the myxobacterium M. xanthus is an orderly process characterized by several sequential stages: growth leads to aggregation leads to formation of raised, darkened mounds of cells leads to autolysis leads to myxospore induction. The temporal sequence of autolysis followed by myxospore induction is consistent with the interpretation that developmental autolysis provides essential requirements for the surviving cells to induce to myxospores. At intermediate developmental times on agar plates a fraction of the cell population is irreversibly committed to lyse; i.e., lysis continues in liquid growth medium or in magnesium-phosphate buffer. Lysis is cell concentration independent and is therefore likely to be by an autolytic mechanism. The lysis sequence can be preliminarily characterized as having an early stage during which deoxyribonucleic acid synthesis continues and a later irreversible stage during which deoxyribonucleic acid synthesis does not occur. Irreversible lysis in liquid growth medium or in magnesium-phosphate buffer is initiated on agar plates during nutrient deprivation and such lysis results in the induction of a fraction of the population to myxospores. This induction is dependent upon the concentration of lysis products, thus providing evidence that developmentally induced autolysis is required for myxospore induction.     

Scanning electron microscopy of polyhydroxyalkanoate degradation by bacteria

Bacterial degradation of sheets of selected polyhydroxyalkanoates by Comamonas sp., Pseudomonas lemoignei and Pseudomonas fluorescens GK13 is reported. Five natural polyhydroxyalkanoates were used, namely poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), a copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate, a copolymer of mainly 3-hydroxyoctanoate and minor amounts of 3-hydroxyhexanoate, and two rubber-like copolymers of saturated and unsaturated hydroxyalkanoic acids that had been modified by electron-beam-induced cross-linking. Each of these polymers was degraded by at least one bacterial strain, the rate of hydrolysis being dependent on the surface area of the polymer exposed to attack. Scanning electron microscopy of partially degraded samples showed that hydrolysis started at the surface and at physical lesions in the polymer and proceeded to the inner part of the material. No evidence for areas of non-degradable polymer was found for any of the polymers analysed, even if the polymer contained chemical cross-links. Received: 24 July 1996 / Accepted: 29 August 1996     

Scanning electron microscopy of four teleostean retinas.

The morphology of the retinas of the goldeye Hiodon alosoides (fam. Hiodontidae), the brook trout Salvelinus fontinalis (fam. Salmonidae), the yellow perch Perca flavescens and the walleye Stizostedion vitreum (fam. Percidae) was studied by SEM. Semi-thin plastic sections of the same retinas were also examined for comparison. Contrary to observation of earlier authors the goldeye retina was found to possess both rods and cones; in the case of the other three fishes' retinas, present observations correspond to previous ones, adding only details. SEM gives an impressive, three dimensil view of the gross surface features of the retinas. Shrinkage during the processing of the specimens for SEM, while not altering the general topography, does induce artifacts in both plexiform layers.     

不同分离方法对子实体形成和粘细菌分离的影响

[目的]基于模拟原位环境策略、可培养粘细菌的营养策略及细菌互作网络,改良分离培养基,以提高分离粘细菌的多样性.[方法]通过添加土壤浸提液、使用不同种类的诱导菌和改变诱导菌的接种方式设置分离方法,同时以传统的分离方法作对照.[结果]改良的分离方法比对照组诱导出了更多粘细菌子实体种类,采自4个地区的9份样品共分离纯化出40...     

Scanning electron microscopy of chloroplast ultrastructure

A range of fracturing and sectioning techniques are now available which permit intracellular structures to be observed in the scanning electron microscope. One such technique, based on the method of Tanaka (1981), has been used to study chloroplast ultrastructure in Japan laurel, Aucuba japonica. Small pieces of leaves were fixed, fractured whilst frozen and transferred to a dilute solution of osmium tetroxide in which cytoplasmic maceration took place. Specimens were dehydrated, critical point dried and examined was required to remove the stroma from fractured chloroplasts. Following this treatment details of the chloroplast envelope, frets, grana and plastoglobuli could be observed. The results were compared with conventionally prepared thin sections examined in the transmission electron microscope and with the three dimensional reconstructions described in the literature.     

Scanning electron microscopy of Penicillium conidia

The morphology of conidia in 211 species and 12 varieties belonging to the genus Penicillium Link ex Gray have been studied and compared.According to surface ornamentation, conidia have been classified into six groups: A, smooth-walled (7% of the species); B, delicately roughened (13%); C, warty (28%); D, echinate (10%); E, striate with low irregular ridges (36%); and F, striate with scarce high ridges or bars (6%). Whereas the first two groups are closely related in both shape and average size, a gradual reduction was observed in size and in the length/width (l/w) ratio in the remaining groups. Echinate conidia were globose, having the largest average size. Only four species produced conidia not surpassing 2 m in diameter. Maximum length observed was 8 m, and most elongated conidia had a l/w ratio of 3.5. Forty per cent of the species studied had globose conidia.Conidia of the monoverticillate species were generally smaller, more globose and frequently with ridges. In the Asymmetrica, the conidia were generally larger, and showed ridges in comparatively few species. Conidia of the Symmetrica, which were frequently striate with ridges, presented the most elongated forms. The largest average size was found in the conidia of the Polyverticillata which were generally warty. Finally, we have considered the variations in surface ornamentation of conidia during the evolution of the genus Penicillium and drawn attention to their possible relationship with certain habitats and ways of conidial dispersion.