Unusual swimming behavior of a magnetotactic bacterium

Magnetotactic bacteria of strain Mar 1–83, when swimming in an applied magnetic field, did not move as a homogeneous cell suspension, but aggregated in distinct wave-like structures. The waves remained stable during forward movement. The number of cells per wave ranged from a few cells in permanent lateral contact to hundreds of bacteria moving visibly within a wave. Wave formation required a horizontal and vertical magnetic component. Electron microscopy indicated at least 3 distinct parallel chains of magnetosomes inside the bacterium. The cellular magnetic dipole moment was determined. Cell-to-cell magnetic interaction could be ruled out as the sole mechanism that induced wave formation and kept waves stable. Other mechanisms are discussed.     

Cell organization and ultrastructure of a magnetotactic multicellular organism

Magnetotactic multicellular aggregates and many-celled magnetotactic prokaryotes have been described as spherical organisms composed of several Gram-negative bacteria capable to align themselves along magnetic fields and swim as a unit. Here we describe a similar organism collected in a large hypersaline lagoon in Brazil. Ultrathin sections and freeze fracture replicas showed that the cells are arranged side by side and face both the external environment and an internal acellular compartment in the center of the organism. This compartment contains a belt of filaments linking the cells, and numerous membrane vesicles. The shape of the cells approaches a pyramid, with the apex pointing to the internal compartment, and the basis facing the external environment. The contact region of two cells is flat and represents the pyramid faces, while the contacts of three or more cells contain cell projections and represent the edges. Freeze-fracture replicas showed a high concentration of intramembrane particles on the edges and also in the region of the outer membrane that faces the external environment. Dark field optical microscopy showed that the whole organism performs a coordinated movement with either straight or helicoidal trajectories. We conclude that the organisms described in this work are, in fact, highly organized prokaryotic multicellular organisms.     

The cytotoxicity of naturally occurring styryl lactones

We extracted and isolated three natural styryl lactones from Goniothalamus griffithii Hook f. Thoms and investigated their cytotoxicity on a panel of three hepatocyte cell lines, HepG2, drug resistant HepG2 (HepG2-R) and primary cultured normal mice hepatocyte in order to find candidates of potential anti-cancer drugs which have low toxicity on normal cells and high effect on tumors or drug resistant tumors. All the three styryl lactones showed evident cytotoxic activities on both HepG2 and HepG2-R cell lines; however, gonithalamin and goniodiol shows less toxicity on normal mice hepatocyte as the IC(50) values of them on normal mice hepatocyte were about three times of that on HepG2. Morphological observation and cell cycle analysis were employed to elucidate the mechanisms of cytotoxicity of the tested compounds. Many apoptotic cells were observed in gonithalamin- and altholactone-treated cells, whereas, cells with chromosomes gathered at the equator were easily found in goniodiol-treated cultures. The analysis of cell cycle showed that G(2)/M arrest contributed to goniothalimin- and gonidiol-caused cell death and apoptosis was the cause of gonithalamin- and altholactone-induced cell death. Our results suggest that the three styryl lactones may be prospectively developed into anti-tumor drugs, especially on treating drug-resistance tumor after structure modification.     

Studies on ultrastructure and composition of cell walls of the cyanobacterium Anacystis nidulans

The multilayered cell wall of the cyanobacterium Anacystis nidulans was studied by the freezeetching technique. A characteristic fracture face in the outer cell wall was demonstrated which is densely packed with particles of a diameter of 60–75 Å. This particle layer is comparable with layers which have been described in many cell walls of Gram-negative prokaryotes.The outer membrane of the cell wall was solubilised by extraction with phenol/water or sodium dodecyl sulfate (SDS). In the SDS-extract 31 bands were separated by polyacrylamide gel electrophoresis, among them 3–5 major proteins with molecular weights of approximately 60, 40, and 10 kdaltons, respectively. Several polypeptides of the Anacystis cell wall were comparable in their mobility with polypeptides extracted from cell walls of different Gramnegative bacteria. The analysis of the SDS-unsoluble electron dense layer (sacculi) revealed the typical components of peptidoglycan diaminopimelic acid, muramic acid, glutamic acid, glucosamine and alamine in the molar ratio of 1.0:0.9:1.1:1.5:1.9. In addition, other amino acids (molar ratio from 0.05–0.36), mannosamine (molar ratio 0.54), and lipopolysaccharide components were detected in low concentration.Abbreviations SDS sodium dodecyl sulfate - EDTA ethylene diamine tetraacetate     

Cell wall of Thermoanaerobacterium thermosulfurigenes EM1: isolation of its components and attachment of the xylanase XynA

Thermoanaerobacterium thermosulfurigenes EM1 has a gram-positive type cell wall completely covered by a surface layer (S-layer) with hexagonal lattice symmetry. The components of the cell envelope were isolated, and the S-layer protein was purified and characterized. S-layer monomers assembled in vitro into sheets with the same hexagonal symmetry as in vivo. Monosaccharide analysis revealed that the S-layer is associated with fucose, rhamnose, mannosamine, glucosamine, galactose, and glucose. The N-terminal 31 amino acid residues of the S-layer protein showed significant similarity to SLH (S-layer homology) domains found in S-layer proteins of different bacteria and in the exocellular enzymes pullulanase, polygalacturonate hydrolase, and xylanase of T. thermosulfurigenes EM1. The xylanase from T. thermosulfurigenes EM1 was copurified with the S-layer protein during isolation of cell wall components. Since SLH domains of some structural proteins have been shown to anchor these proteins noncovalently to the cell envelope, we propose a common anchoring mechanism for the S-layer protein and exocellular enzymes via their SLH domains in the peptidoglycan-containing layer of T. thermosulfurigenes EM1. Received: 23 October 1998 / Accepted: 21 December 1998     

降解菌HN36对二氯喹啉酸胁迫下烟草茎尖和叶片超微结构的影响

利用降解菌HN36降解土壤中的二氯喹啉酸及修复土壤的生态环境, 为稻田植烟地区烟叶安全生产提供技术和理论依据。采用盆栽试验, 将二氯喹啉酸与降解菌HN36配成一定量的溶液, 均匀喷洒到过筛的干土中, 将5叶期烟苗移栽到处理的塑料盆土中。当烟苗长到8叶期时分别取茎尖﹑顶叶和中部叶进行处理, 在电镜下观察细胞超微结构变化, 利用高效液相色谱仪检测土壤中二氯喹啉酸降解的动态。烟株细胞超微结构变化的程度有差异, 表现为受害烟株>修复烟株>健康烟株; 烟株的茎尖和顶叶细胞伤害最严重, 中部叶片细胞伤害较轻。研究结果还显示, 在含二氯喹啉酸的土壤中, 加入降解菌HN36能加速二氯喹啉酸降解, 改善土壤健康质量, 烟株细胞超微结构及烟叶品质明显得到修复。     

蝶类复眼小眼面表面超微结构的比较研究

利用扫描电子显微镜观察了6种蝶复眼小眼面的表面结构。发现小眼面表面覆盖着均匀的小圆形凸起颗粒,在中央处有一由凹凸及纹褶构成的特殊结构。这种结构在蝶类各科之间有明显区别,表现其各自的不同特征。     

Mutagenesis of conserved charged amino acids in SLH domains of Thermoanaerobacterium thermosulfurigenes EM1 affects attachment to cell wall sacculi

SLH domains (for surface layer homology) are involved in the attachment of proteins to bacterial cell walls. The data presented here assign the conserved TRAE motif within SLH domains a key role for the binding. The charged amino acids arginine (R) or/and glutamic acid (E) were replaced via site-directed mutagenesis by different amino acids. Effects were visualized in an in vitro binding assay using native cell wall sacculi of Thermoanaerobacterium thermosulfurigenes EM1 and different variants of an SLH protein which consisted of the triplicate SLH domain of xylanase XynA of this bacterium and which was purified after expression in Escherichia coli. The results indicated (1) that the TRAE motif is critical for the binding function of SLH domains, (2) that a functional TRAE motif is necessary in all three domains, (3) that a least one (preferentially positively) charged amino acid in the TRAE motif is required for the functionality of the SLH domain, and (4) that the position of the negatively and positively charged amino acids is important. The finding that the cell wall of T. thermosulfurigenes EM1 contains pyruvate (4 μg mg⁻¹) is in agreement with the hypothesis that pyruvylated secondary cell wall polymers function as ligand for SLH domains.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Structural and chemical characterization of S-layers of selected strains ofBacillus stearothermophilus andDesulfotomaculum nigrificans

The structures, amino acid- and neutral sugar compositions of the crystalline surface layers (S-layers) of four selected strains each ofBacillus stearothermophilus andDesulfotomaculum nigrificans were compared. Among the four strains of each species a remarkable diversity in the molecular weights of the S-layer subunits and in the geometry and constants of the S-layer lattices was apparent. The crystalline arrays included hexagonal (p6), square (p4) and oblique (p2) lattices. In vitro self-assembly of isolated S-layer subunits (or S-layer fragments) led to the formation of flat sheets or open-ended cylindrical assembly products. The amino acid composition of the S-layers exhibited great similarities and was predominantly acidic. With the exception of the S-layers of two strains ofB. stearothermophilus (where only traces of neutral sugars could be detected), all other S-layer proteins seemed to be glycosylated. Among these strains significant differences in the amount and composition of the glycan portions were found. Based on this diversity interesting questions may be asked about the biological significance of the carbohydrate units of glycoproteins in prokaryotic organisms.     

Effect of the lipopeptide antibiotic, iturin A, on morphology and membrane ultrastructure of yeast cells

Abstract The effects of iturin A, at fungicidal concentrations, on yeast cells were studied by scanning electron microscopy and by transmission electron microscopy. A depression, observed in each iturin A-treated cell, was the consequence of the release of electrolytes and other cytoplasmic components. Iturin A passes through the cell wall and disrupts the plasma membrane with the formation of small vesicles and the aggregation of intramembranous particles. Moreover, iturin A passes through the plasma membrane and interacts with the nuclear membrane and probably with membranes of other cytoplasmic organelles.     

Evidence for the glycoprotein nature of the crystalline cell wall surface layer of Bacillus stearothermophilus strain NRS2004/3a

The surface layer of Bacillus stearothermophilus strain NRS2004/3a was isolated and chemically characterized. The results of these initial studies lead to the conclusion that the cell surface protein is glycosylated.     

Acinar ultrastructure of the submandibular gland of Mus musculus during embryonic development

Summary The development of the submandibular gland of the mouse was studied by means of electron microscopy, from the 14th day of gestation up to birth. In the first two days the acini are solid and their cells contain polyribosomes and a few lamellae of endoplasmic reticulum. Beginning with the 16th day secretory granules appear and rapidly fill an increasing number of cells. The different electron density of the granules makes it possible to distinguish 1. two types of granules, dense and pale, and sometimes intermediate ones, 2. polymorphic granules. The latter consists of electron dense and electron pale parts combined in different configurations. The possible significance of the various types of granules is discussed.     

Changes of dictyosome ultrastructure during the cell cycle in onion root meristematic cells. A morphometric and stereological study

Summary Dictyosome ultrastructure changes during the cell cycle in onion root meristematic cells. Changes were mainly related to cisternae and intercisternal spaces morphology. Taking each dictyosome to be composed of three different regions (CIS, medial, and TRANS), several quantitative changes were detected in some of the compartments. Many of the planimetric parameters evaluated showed higher values in medical cisternae, while CIS and TRANS remained nearly constant. We have also found an increased activity of dictyosomes, as indicated by increase in the volume fraction of vesicular attached structures. This reaches maximum values at ana-telophase in coincidence with the onset and progression of cytokinesis.Abbreviations A anaphase - Ac mean area occupied by cisternae per stack section - C CIS - CCS cell cycle stage - D_A mean total dictyosome area - I_SA mean area occupied by intercisternal spaces per stack section - M metaphase - N mean number of cisternae per stack - P prophase - S.E. standard error - T telophase - T TRANS - V_v volume density     

Tegumental ultrastructure of adult Gynaecotyla squatarolae (Digenea: Microphallidae)

Gynaecotyla squatarolae (Digenea: Microphallidae) adult flukes were recovered from experimental chicks at day 4-6 post-infection and their tegumental ultrastructure was observed with a scanning electron microscopy. They were pyriform in shape, and their anterior halves were concaved ventrally. The whole body surface was covered with tegumental spines, which were wide and 16-17 digitated between oral and ventral suckers. The density of spines and number of digits decreased posteriorly. The oral sucker was subterminal and the excretory pore was at the posterior end of the worm. Two ventral suckers were similar in appearance and protruded near midline of the worm. The genital atrium was dextral to the small ventral sucker. The dorsal surface was covered with tegumental spines, but the spines were sparser than on the ventral surface. On the middle portion of the dorsal surface, a small opening presumed to be the Laurer's canal was seen. From these findings, it has been confirmed that the adult G. squatarolae has unique characteristics in the surface ultrastructure.     

Developmental surface ultrastructure of Macroorchis spinulosus in albino rats

Developmental surface ultrastructure of Macroorchis spinulosus was studied by scanning electron microscopy. One-day-old juvenile fluke was leaf-shaped and bent ventrally. Body surface was covered densely with peg-like spines and with cobblestone-like cytoplasmic processes. Ciliated sensory papillae were concentrated around oral sucker. Several unciliated sensory papillae occurred equidistantly on oral sucker and acetabulum. The ciliated papillae appeared in two longitudinal lines symmetric bilaterally on dorsal surface. On adult flukes, tegumantal spines became wider in middle of the body surface. The cytoplasmic processes differentiated into more fine velvety form. It is likely that the differentiated fine cytoplasmic processes are an increased absorptive surface to adult M. spinulosus. It is suggested that single pointed tegumental spines on anterior half of the body may be supportive for this fluke to migration.     

Ribeiroia marini: Surface ultrastructure of redia,cercaria, and adult

Rediae, cercariae, and adults of Ribeiroia marini were examined using a scanning electron microscope to determine the types of tegumental sensory structures and their locations. Sensory structures were observed among numerous tegumental folds in the area immediately surrounding the mouth of the rediae. These sensory structures are similar in appearance, location and fine structure to sensory structures described from the anterior tips of rediae known to be predacious on the sporocysts of Schistosoma mansoni. These uniciliated structures may function as chemoreceptors to aid the redia in migration through snail tissue. Five types of sensory structures bearing one, two, or multiple cilia were distinguishable on the cercariae. These structures were located on and around the oral sucker, dorsal and ventral body surfaces and on the tail. They may be used by the cercariae to locate the intermediate host fish and to find suitable sites within the lateral line scales for encystment. The ventral surface of the adult fluke is covered with spines and shows an absence of sensory structures on the general body surface. Sensory structures were seen in the area surrounding the oral and ventral suckers. The extended cirrus organ has a folded tegument, but lacks spines or sensory structures.     

Conidial surface ultrastructure of human-pathogenic and saprobicCladosporium species

Freeze-fracturing of outer wall layers ofCladosporium conidia revealed two types of ultrastructure, coinciding with taxonomic characteristics. The outer conidial layers were essentially smooth in the human pathogenic species,C. bantianum, C. carrionii, andC. trichoides. In contrast, mosaic arrays of rodlets on conidia were observed with freeze-fracturing in the saprobic species,C. cladosporioides, C. coralloides, C. herbarum, C. sphaerospermum, andC. variabile. Conidia ofC. elatum were an exception among the saprobic species as they had smooth surfaces. The present study supports the suggestion that the human pathogenicCladosporium species should be transferred to another genus.     

Surface ultrastructure of Metagonimus miyatai metacercariae and adults

A scanning electron microscopic study was performed to observe surface ultrastructures of excysted metacercariae and adults of Metagonimus miyatai. Metacercariae were collected from the scale of the pale chub (Zacco platypus), and adult flukes were harvested 1-4 weeks after infection to rats. In excysted metacercariae, the oral sucker was devoid of tegumental spines and had type I and type II sensory papillae. Anteriorly to the ventral sucker, spines were dense and digitated into 5-7 points, whereas near the posterior end of the body spines were sparse and digitated into 2-3 points. In one-week adults, 7 type II sensory papillae were arranged around the lip of the oral sucker, and at inner side of the lip one pair of small and two pairs of large type 1 sensory papillae were seen on each side. The distribution of tegumental spines was similar to that of metacercariae, but they were more differentiated with 9-11 pointed tips. In two- to four-week old adults, the surface ultrastructure was nearly the same as in one-week old adults, however, sperms were frequently seen entering into the Laurer''s canal. Conclusively, the surface ultrastructure of M. miyatai was generally similar to that of M. yokogawai, however, differentiation of tegumental spines and distribution of sensory papillae around the oral sucker were different between the two species, which may be of taxonomic significance.