The lattice arrangement of the collagen fibres in the submucosa of the rat small intestine: scanning electron microscopy

Summary The three-dimensional architecture of the submucosal collagen fibres of the rat (3 weeks old) small intestine was examined by scanning electron microscopy using a selective microdissection method. The main framework of the submucosa was composed of two arrays of collagen fibre bundles running diagonally around the intestinal wall, one set in a clockwise direction, the other counterclockwise. These fibre bundles were about 5 m in diameter and were oriented at a range of angle ± 30°–50° to the longitudinal axis of the intestine. With the advantage of the SEM observation it was demonstrated that these fibres in different arrays did not constitute two separate layers but interwove to form a unified lattice sheet. An irregular network of fine collagen fibrils over the main framework was also seen. The significance of their arrangement is discussed with respect to the skeletal function of the submucosa in the intestine.     

Orientation of microfibrils and microtubules in developing tension-wood fibres of Japanese ash (Fraxinus mandshurica var. japonica)

The orientation of cellulose microfibrils (MFs) and the arrangement of cortical microtubules (MTs) in the developing tension-wood fibres of Japanese ash (Fraxinus mandshurica Rupr. var. japonica Maxim.) trees were investigated by electron and immunofluorescence microscopy. The MFs were deposited at an angle of about 45° to the longitudinal axis of the fibre in an S-helical orientation at the initiation of secondary wall thickening. The MFs changed their orientation progressively, with clockwise rotation (viewed from the lumen side), from the S-helix until they were oriented approximately parallel to the fibre axis. This configuration can be considered as a semihelicoidal pattern. With arresting of rotation, a thick gelatinous (G-) layer was developed as a result of the repeated deposition of parallel MFs with a consistent texture. Two types of gelatinous fibre were identified on the basis of the orientation of MFs at the later stage of G-layer deposition. Microfibrils of type 1 were oriented parallel to the fibre axis; MFs of type 2 were laid down with counterclockwise rotation. The counterclockwise rotation of MFs was associated with a variation in the angle of MFs with respect to the fibre axis that ranged from 5° to 25° with a Z-helical orientation among the fibres. The MFs showed a high degree of parallelism at all stages of deposition during G-layer formation. No MFs with an S-helical orientation were observed in the G-layer. Based on these results, a model for the orientation and deposition of MFs in the secondary wall of tension-wood fibres with an S₁ + G type of wall organization is proposed. The MT arrays changed progressively, with clockwise rotation (viewed from the lumen side), from an angle of about 35–40° in a Z-helical orientation to an angle of approximately 0° (parallel) to the fibre axis during G-layer formation. The parallelism between MTs and MFs was evident. The density of MTs in the developing tension-wood fibres during formation of the G-layer was about 17–18 per m of wall. It appears that MTs with a high density play a significant role in regulating the orientation of nascent MFs in the secondary walls of wood fibres. It also appears that the high degree of parallelism among MFs is closely related to the parallelism of MTs that are present at a high density.Abbreviations FE-SEM field emission scanning electron microscopy - G gelatinous layer - MF cellulose microfibril - MT cortical microtubule - S₁ outermost layer of the secondary wall - TEM transmission electron microscopy We thank Dr. Y. Akibayashi, Mr. Y. Sano and Mr. T. Itoh of the Faculty of Agriculture, Hokkaido University, for their experimental or technical assistance.     

Chromosome organization revealed upon the decondensation of telophase chromosomes inAllium

Chromosomes of root tip cells ofAllium cepa andAllium sativum were studied in early, middle and late telophase to examine the organization of mitotic chromosomes, taking advantage of the naturally occurring chromosome dispersion during the process of decondensation in telophase. Longitudinal and transverse sections of telophase chromosomes viewed under the transmission electron microscope showed that mitotic chromosomes inAllium were composed of helically coiled 400–550 nm chromatin fibres. In some regions of the longitudinal sections, these chromatin fibres were seen to be orientated parallel to one another but formed roughly a right angle to the long axis of the chromosome. In transverse sections, the telophase chromosome appeared to have a hollow centre encircled by the 400–550 nm chromatin fibre which in turn was a hollow tube structure formed by the coiling of a thinner fibre of 170–200 nm. In addition, cross views of chromatin fibres of 170–200 nm and 50–70 nm were also identified in telophase chromosome preparations. These two organizational levels of chromatin fibres also showed a hollow centre. The process of decondensation of telophase chromosomes is described, and some morphological characteristics associated with the activities of chromosome decondensation are analysed. Based on the observations made onAllium chromosomes in this study, various models of chromosome organization are discussed.     

Arrangement of smooth muscle cells and intramuscular septa in the taenia coli

Summary Bands of electron-dense material beneath the cell membrane of smooth muscle cells of the guinea-pig taenia coli provide attachment to thin myofilaments and to intermediate (10 nm) filaments; about 50% of the cell membrane is occupied by dense bands in muscle cells transversely sectioned at the level of their nucleus, and between 50 and 100% in smaller cell profiles nearer the cell's ends. In addition to the known cell-to-cell junctions (intermediate contacts), more complex apparatuses anchor muscle cells together, either end-to-end or end-to-side or side-to-side. They consist of elaborate folds, invaginations and protrusions accompanied by large amounts of basal lamina material. In the end-to-end anchoring apparatuses numerous finger-like and laminar processes from the two cells interdigitate. Other muscle cells have a star-shaped profile in the last few microns of their length, or show longitudinal invaginations occupied by a thickened basal lamina and occasionally by collagen fibrils. The septa of connective tissue extend only for a few hundred microns along the length of the taenia. In taeniae fixed in condition of mild stretch the muscle cells form an angle of about 5° with the septa. In muscles fixed during isotonic contraction the angle increases to about 20–22°, and in longitudinal sections the muscle cells appear arranged in a herring-bone pattern. The collagen concentration in the taenia coli is 4–6 times greater that in skeletal and cardiac muscles. These various structures are discussed in terms of their possible role in the mechanism of force transmission.I thank Mr. S.J. Sarsfield and Miss E.M. Franke for expert technical assistance, and Dr. Adam Yamey for much help in the experiments on collagen content. This work is supported by grants from the Medical Research Council     

Effects of temperature on the properties of primary auditory fibres of the spectacled caiman,Caiman crocodilus (L.)

Summary The effect of temperature on the response properties of primary auditory fibres in caiman was studied. The head temperature was varied over the range of 10–35 ° C while the body was kept at a standard temperature of 27 °C (T_s). The temperature effects observed on auditory afferents were fully reversible. Below 11 °C the neural firing ceased.The mean spontaneous firing rate increased nearly linearly with temperature. The slopes in different fibres ranged from 0.2–3.5 imp s^–1 °C^–1. A bimodal distribution of mean spontaneous firing rate was found (<20 imp s^–1 and >20 imp s^–1 at T_s) at all temperatures.The frequency-intensity response area of the primary fibres shifted uniformly with temperature. The characteristic frequency (CF) increased nearly linearly with temperature. The slopes in different fibres ranged from 3–90 Hz °C^–1. Expressed in octaves the CF-change varied in each fibre from about O.14oct °C^–1 at 15 °C to about 0.06 oct °C^–1 at 30 °C, irrespective of the fibre's CF at T_s. Thresholds were lowest near T_s. Below T_s the thresholds decreased on average by 2dB°C^–1, above T_s the thresholds rose rapidly with temperature. The sharpness of tuning (Q_10db) showed no major change in the temperature range tested.Comparison of these findings with those from other lower vertebrates and from mammals shows that only mammalian auditory afferents do not shift their CF with temperature, suggesting that a fundamental difference in mammalian and submammalian tuning mechanisms exists. This does not necessarily imply that there is a single unifying tuning mechanism for all mammals and another one for non-mammals.Abbreviations BF best frequency: frequency of maximal response at an intensity 10 dB above the CF-threshold - CF characteristic frequency - FTC frequency threshold curve, tuning curve - T _s standard temperature of 27 °C     

Influence of adequate vestibular stimulation on locomotor activity in the guinea pig forelimb muscles. Tilting in relation to the longitudinal axis

The influence of adequate vestibular stimulation occurring as the animal tilted around longitudinal axis on locomotor activity of the forelimb muscles was investigated during experiments on guinea pigs decerebrated at precollicular level. Locomotor activity was produced by electrical stimulation of the mesencephalic locomotor region. An increase in extensor EMG activity was observed when the animal shifted its weight onto the limb ipsilateral to the tilt during the "standing" phase and a reduction in flexor activity during the swing phase. The reverse of these changes was seen in the activity of antagonist muscles in the contralateral limb. It was found that changes in muscular locomotor activity exceeded those observed during animal movements by 60–40° in the extensors and 40–20° in the flexors during cyclic sinusoidal tilting in the 0.02–0.4 Hz range. The mechanisms underlying vestibular control of locomotor activity are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 534–541, July–August, 1987.     

Thermal dependence of contractile properties of single skinned muscle fibres from Antarctic and various warm water marine fishes including Skipjack Tuna (Katsuwonus pelamis) and Kawakawa (Euthynnus affinis)

Summary Single fast fibres and small bundles of slow fibres were isolated from the trunk muscles of an Antarctic (Notothenia neglecta) and various warm water marine fishes (Blue Crevally,Carangus melampygus; Grey Mullet,Mugil cephalus; Dolphin Fish,Coryphaena hippurus; Skipjack-tuna,Katsuwonus pelamis and Kawakawa,Euthynuus affinis). Fibres were chemically skinned with the nonionic detergent Brij 58.For warm water species, maximum Ca²⁺-activated tension (P ₀) almost doubled between 5–20°C with little further increase up to 30°C. However, when measured at their normal body temperatures,P ₀ values for fast fibres were similar for all species examined, 15.7–22.5 N · cm^–2. Ca²⁺-regulation of contraction was disrupted at temperatures above 15°C in the Antarctic species, but was maintained at up to 30°C for warm water fish.Unloaded (maximum) contraction speeds (V _max) of fibres were determined by the slacktest method. In general,V _max was approximately two times higher in white than red muscles for all species studied, except Skipjack tuna. For Skipjack tuna,V _max of superficial red and white fibres was similar (15.7 muscle lengths · s^–1 (L ₀ · s^–1)) but were 6.5 times faster than theV _max of internal red muscle fibres (2.4±0.2L ₀ · s^–1) (25°C). V _max forN. neglecta fast fibres at 0–5°C (2–3L ₀ · s^–1) were similar to that of warm water species measured at 10–20°C. However, when measured at their normal muscle temperatures, theV _max for the fast muscle fibres of the warm water species were 2–3 times higher than that forN. neglecta.In general,Q _{10(15–30°C)} values forV _max were in the range 1.8–2.0 for all warm water species studied except Skipjack tuna.V _max for the internal red muscle fibres of Skipjack tuna were much more temperature dependent (Q _{10(15–30°C)}=3.1) (P<0.01) than for superficial red or white muscle fibres. The proportion of slower red muscle fibres in tuna (28% for 1 kg Skipjack) is 3–10 times higher than for most teleosts and is related to the tuna's need to sustain high cruising speeds. We suggest that the 8–10°C temperature gradient that can exist in Skipjack tuna between internal red and white muscles allows both fibre types to contract at the same speed. Therefore, in tuna, both red and white muscle may contribute to power generation during high speed swimming.     

Stomach stress and strain depend on location, direction and the layered structure

The stomach is as other parts of the gastrointestinal tract functionally subjected to dimensional change. Hence, the biomechanical properties are of functional importance. Our group has previously demonstrated that the stress–strain properties of the rat and rabbit stomach wall were species-, location- and direction-dependent. We further wanted to study the anisotropic biomechanical properties of the stomach wall in pigs. Furthermore, we made an in-depth biomechanical test on the layered wall of the stomach in different regions. Two stomach strips were cut both in longitudinal direction (parallel with the greater curvature) and circumferential direction (perpendicular to the greater curvature) from the gastric fundus, corpus and antrum. One strip was used for the non-separated (intact) wall test and the other one was separated for the test on the mucosa–submucosa and muscle layers individually. The length, thickness and width of each strip were measured from digital images. The uni-axial stress and strain were computed from the force generation and the tissue strip deformation during stretching. The muscle layer was the thickest in the antrum whereas the mucosal–submucosal layer was the thickest in the corpus of the stomach (P<0.01). The strips from the corpus were stiffest among the three regions in both longitudinal and circumferential directions (P<0.001). The longitudinal strips was stiffer than the circumferential strips in all three regions (P<0.001) and the mucosa–submucosa strips was stiffer than the intact wall and the muscle layer in both directions for the fundus and the corpus (P<0.001). The constant a of the intact wall and mucosa–submucosa layer was in both directions linearly associated with the mucosa–submucosa thickness. In conclusion, the uni-axial stress–strain curves of pig stomach were location-, direction- and layer-dependent. The stiffer wall in the corpus is likely due to its thicker mucosa, i.e., the stiffness of the mucosa–submucosa layer seems can explain the intact wall stiffness. Since the structure and function of the pig stomach are similar to the human stomach, we believe that the data obtained from this study can be extended to humans. Detailed biomechanical mapping of the stomach will likely help us to understand physiological functions of the different parts of the human stomach, such as gastric accommodation and mechanosensation.     

Effects of adequate vestibular stimulation on locomotor activity in the guinea pig fore- and hindlimb muscles. Tilting around a transverse axis

The effects of adequate vestibular stimulation occurring as the animal tilted around its transverse axis on locomotor activity of the fore- and hindlimb muscles produced by electrical brainstem stimulation were investigated during experiments on guinea pigs decerebrated at the precollicular level. An increase and decrease in forelimb and hindlimb extensor activity, respectively, at the standing phase of the locomotor cycle were observed when the animal was tilted head-downward. The reverse changes took place in the limb extensor muscles when the animal was tilted head-up. Forelimb extensor activity during the swing phase increased and decreased when the animal was tilted head-up and head-downward, respectively. Phase shifts of changes in locomotor activity of the forelimb extensors altered from 60 to –30°, from –150 to 220° in hindlimb extensors, and from –140 to –220° in forelimb flexors during sinusoidal tilting in the 0.02–0.4 Hz frequency range and an amplitude of ±20°. Mechanisms underlying the changes observed in locomotor muscle activity are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 833–838, November–December, 1987.     

The structure of calcified tendon

Summary The small angle X-ray scattering from unheated and heated calcified chicken tendon has been accurately measured using an automatically recording Kratky camera. A two-dimensional optical diffraction pattern of electron micrographs has been recorded and is in excellent agreement with the small angle X-ray diffraction pattern.The wide and small angle X-ray diffraction pattern, the Fraunhofer diffraction pattern, electron microscopic appearance, and a Fourier synthesis are mutually consistent, and indicate that the crystalline fraction of apatite in normal calcified tendon exists in the form of well oriented crystallites of about 330 Å in length and 50–60 Å in width with the long axis being parallel to the local fibre axis. The separate crystallites are largely located in parallel rows which repeat every 660 Å in the longitudinal direction of the tendon.Analysis of the small angle equatorial scattering shows the crystallites to be clustered together into three well-defined groups with diameters of about 60 Å, 190 Å, and 400 Å. It is suggested that the largest clusters are located in between the collagen fibrils and correspond to the primary calcification.This work was carried out under the supervision of Professor Arne Engström (Head of the Department of Medical Physics, Karolinska Institutet, Stockholm) while the author held a Longterm Fellowship from the European Molecular Biology Organization.     

Directionality of antennal sweeps elicited by water jet stimulation of the tailfan in the crayfish Procambarus clarkii

Summary Directionality and intensity dependence of antennal sweeps elicited by water jet stimulation of the tailfan in tethered, reversibly blinded adult and juvenile crayfish (Procambarus clarkii) were analyzed.Resting crayfish keep their antennae at about 50° symmetrically to the longitudinal body axis (Figs. 2 bottom, and 3).In adults, tailfan stimulation elicits synchronous backward sweeps of both antennae, which increase for more caudal stimulus directions (Figs. 2–4 and 5A). Directions differing by 30°–60° are significantly distinguished (Fig. 4). The mean sweep of the ipsilateral antenna significantly overrides that of the contralateral antenna for rostrolateral stimulation at 40–200 mm/s stimulus velocity and lateral to caudolateral stimulation at 40 mm/s and thus lateralization of the stimulus is revealed (Figs. 2 top, 4 and 5A). Mean antennal sweeps at a given stimulus direction and distance increase with increasing stimulus velocity (40–250 mm/s, Fig. 5A).In juveniles, the directional dependence of antennal sweeps is reduced compared to that of adults, while a similar intensity dependence is found (Fig. 5B).The pronounced directionality of the antennal response in adult crayfish vanishes and response latencies increase after reversibly covering the tailfan with a small bag or the telson with waterproof paste (Figs. 6 and 7). Thus, tailfan and especially telson mechanoreceptors play an important role in the localization of water movements elicited by predators or prey behind the crayfish.     

Methanotrophs of the Psychrophilic Microbial Community of the Russian Arctic Tundra

In tundra, at a low temperature, there exists a slowly developing methanotrophic community. Methane-oxidizing bacteria are associated with plants growing at high humidity, such as sedge and sphagnum; no methanotrophs were found in polytrichous and aulacomnious mosses and lichens, typical of more arid areas. The methanotrophic bacterial community inhabits definite soil horizons, from moss dust to peat formed from it. The potential ability of the methanotrophic community to oxidize methane at 5°C enhances with the depth of the soil profile in spite of the decreasing soil temperature. The methanotrophic community was found to gradually adapt to various temperatures due to the presence of different methane-oxidizing bacteria in its composition. Depending on the temperature and pH, different methanotrophs occupy different econiches. Within a temperature range from 5 to 15°C, three morphologically distinct groups of methanotrophs could be distinguished. At pH 5–7 and 5–15°C, forms morphologically similar to Methylobacter psychrophilus predominated, whereas at the acidic pH 4–6 and 10–15°C, bipolar cells typical of Methylocella palustris were mostly found. The third group of methanotrophic bacteria growing at pH 5–7 and 5–10°C was represented by a novel methanotroph whose large coccoid cells had a thick mucous capsule.     

Effects of adequate vestibular stimulation on evoked rhythmic activity in the forelimb nerves of immobilized guinea pigs

The effects of adequate vestibular stimulation, achieved by turning the animal around its longitudinal axis, on intensity of rhythmic activity in forelimb muscle nerves were investigated during experiments on immobilized decerebrate guinea pigs. This activity was produced by electrical stimulation of the mesencephalic locomotor region, following the action of DOPA administered i.v. Rhythmic activity arises mainly in the flexor muscle nerve under these circumstances. The intensity of such activity alters as the body was tilted, diminishing and increasing as the body is tilted to the ipsi- and contralateral side, respectively. Alterations in activity are characterized by an acceleration-related phase lag of –110 to –150° during cyclic tilting at the rate of 0.02–0.4 Hz.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 223–227, March–April, 1990.     

Ultrastructural visualization of elastic fibres with a tannate-metal salt method

Summary A modification of the tannic acid-metal salt method was applied as an ultrastructural stain for elastin. Thin sections of glutaraldehyde-fixed, embedded rat aorta and rabbit elastic cartilage, with and without osmication, were examined. Raising the pH of the tannic acid solution from 2.7 to 9.0 progressively increased the electron-density of elastic fibres and collagen fibrils in osmicated and unosmicated specimens. The maximum tannic acid staining of elastic fibres was observed in the pH range 7.0–9.0. Collagen staining, although less intense than that of elastic fibres, was also greatest in this pH range. Elastic fibres in osmicated specimens demonstrated the strongest tannic acid staining with a minimal increase in density of collagen and cell nuclei when compared to the unosmicated specimens. Sequential treatments of osmicated specimens with tannic acid pH 7.0–9.0, and uranyl acetate, pH 4.1, enhanced the density of the elastin intensely, increased collagen staining moderately, but hardly increased the density of nuclei and microfibrils. In elastase-digested osmicated specimens, all tannic acid (pH 7.0)-uranyl acetate-reactive elastin was selectively removed. These results demonstrate that all the neutral and alkaline tannic acid-uranyl acetate methods can be used as a postembedment stain for elastin specimens fixed in glutaraldehyde and osmium tetroxide.     

Biomechanical remodelling of obstructed guinea pig jejunum

Data on morphological and biomechanical remodelling are needed to understand the mechanisms behind intestinal obstruction. The effect of partial obstruction on mechanical properties with reference to the zero-stress state and on the histomorphological properties of the guinea pig small intestine was determined in this study. Partial obstruction and sham operation were surgically created in mid-jejunum of guinea pigs. The animals survived 2, 4, 7, and 14 days. The age-matched guinea pigs that were not operated served as normal controls. The segment proximal to the obstruction site was used for histological analysis, no-load state and zero-stress state data, and distension test. The segment for distension was immersed in an organ bath and inflated to 10 cm H₂O. The outer diameter change during the inflation was monitored using a microscope with CCD camera. Circumferential stresses and strains were computed from the diameter, pressure and the zero-stress state data. The opening angle and absolute value of residual strain decreased (P<0.01 and P<0.001) whereas the wall thickness, wall cross-sectional area, and the wall stiffness increased after 7 days obstruction (P<0.05, P<0.01). Histologically, the muscle and submucosa layers, especially the circumferential muscle layer increased in thickness after obstruction. The opening angle and residual strain mainly depended on the thickness of the muscle layer whereas the wall stiffness mainly depended on the thickness of the submucosa layer. In conclusion, the histomorphological and biomechanical properties of small intestine (referenced for the first time to the zero-stress state) remodel proximal to the obstruction site in a time-dependent manner.     

Scanning electron microscopy of the muscle coat of the guinea-pig small intestine

Summary We have studied the layers of the muscular coat of the guinea-pig small intestine after enzymatic and chemical removal of extracellular connective tissue. The cells of the longitudinal muscle layer are wider, have rougher surfaces, more finger-like processes and more complex terminations, but fewer intercellular junctions than cells in the circular muscle layer. A special layer of wide, flat cells with a dense innervation exists at the inner margin of the circular muscle layer, facing the submucosa. The ganglia of the myenteric and submucosal plexuses are covered by a smooth basal lamina, a delicate feltwork of collagen fibrils, and innumerable connective tissue cells. The neuronal and glial cell processes at the surface of ganglia form an interlocking mosaic, which is loosely packed in newborn and young animals, but becomes tightly packed in adults. The arrangement of glial cells becomes progressively looser along finer nerve bundles. Single varicose nerve fibres are rarely exposed, but multiaxonal bundles are common. Fibroblast-like cells of characteristic shape and orientation are found in the serosa; around nerve ganglia; in the intermuscular connective tissue layer and in the circular muscle, where they bridge nerve bundles and muscle cells; at the submucosal face of the special, flattened inner circular muscle layer; and in the submucosa. Some of these fibroblast like cells correspond to interstitial cells of Cajal. Other structures readily visualized by scanning electron microscopy are blood and lymphatic vessels and their periendothelial cells. The relationship of cellular elements to connective tissue was studied with three different preparative procedures: (1) freeze-cracked specimens of intact, undigested intestine; (2) stretch preparations of longitudinal muscle with adhering myenteric plexus; (3) sheets of submucosal collagen bundles from which all cellular elements had been removed by prolonged detergent extraction.     

Evidence that myenteric neurons of the gastric corpus project to both the mucosa and the external muscle: myectomy operations on the canine stomach

Summary The distribution of nerve cell bodies and fibres in the canine stomach was investigated using antibodies to the general neuronal marker, neuron-specific enolase. Prominent ganglia containing many reactive nerve cells were found in the myenteric plexus of the gastric corpus and antrum. Nerve cells were absent from the submucosa of the corpus and were extremely rare in the antrum. Renoval of areas of longitudinal muscle and myenteric plexus from the corpus (myectomy), with 7 days allowed for axon degeneration, resulted in the loss of fibres reactive for galanin, gastrin-releasing peptide, substance P and vasoactive intestinal peptide from both the circular muscle and mucosa in the area covered by the lesion. Combined vagotomy and sympathetic denervation did not significantly affect these fibres, but did cause fibres reactive for calcitonin gene-related peptide to degenerate. It is concluded that the myenteric plexus of the gastric corpus, like the myenteric plexus of the small intestine and colon, is the source of nerve fibres innervating the circular muscle, but, in contrast to other regions of the gastrointestinal tract, myenteric ganglia, not submucous ganglia, are the major, or sole, source of the intrinsic innervation of the mucosa.     

Visualization of the supramolecular architecture of chlorosomes (chlorobium type vesicles) in freeze-fractured cells of Chloroflexus aurantiacus

Freeze-fracture electron microscopy has been used to investigate the size, form, distribution and supramolecular organization of chlorosomes (chlorobium type vesicles) in Chloroflexus aurantiacus J-10fl, a phototrophic, filamentous gliding bacterium. The chlorosomes, that appear tightly attached to the cytoplasmic membrane, have the form of flat, elongated sacs with rounded ends, and measure 106±24×32±10×12±2nm. They are randomly distributed, and in most instances their longitudinal axis makes an angle of 30–60° to the filament axis. Each chlorosome consists of a core and an approx. 2 nm thick envelope. The core is filled with rod-shaped elements (approx. 5.2 nm in diameter) made up of globular subunits with a periodicity of approx. 6 nm. The rod elements extend the full length of the chlorosome. The membrane-associated envelope layer is marked by extremely fine striations with a repeating distance of 2.5–3nm, while the envelope layer adjacent to the cytoplasm exhibits no discernable substructure. The margins of the vesicles are delineated by regularly spaced 7 nm particles.No information is yet available on the organization of the cytoplasmic membrane areas to which the vesicles are attached since the fracture plane always passes into the adjacent vesicles in such region rather than continuing through the membrane. Upon cooling of the cells large particle-free areas develop in the cytoplasmic membrane. Simultaneously the chlorosomes become crowded into the remaining particle-rich areas, where some seem to fuse with each other to formAbbreviation bchl bacteriochlorophyll