Examination of 20 Bacillus species by crossed immunoelectrophoresis under taxonomic aspects

In order to examine the efficiency of crossed immunoelectrophoresis (CIE) for the differentiation of species and for the determination of taxonomic relationships within the genus Bacillus, an investigation including strains of 20 species was performed. Ultrasonic extracts (USE) of sporefree-grown vegetative cells were used. With rabbit antisera against USE of type strains, the CIE was accomplished in homologous and heterologous combinations. USE's of additional strains were included into this investigation. In order to evaluate the immunoelectropherograms, the number of precipitates was counted. A mean of 103 precipitates was found in homologous reactions. With few exceptions, heterologous combinations showed less similarity in the number of antigens. Because of their high cross-reactions, the following species could not be differentiated: B. subtilis from B. amyloliquefaciens and strains of B. coagulans, furthermore, B. cereus from B. thuringiensis. The different species revealed lower numbers of precipitates with decreasing taxonomic relationships in heterologous combinations. This observation was used to classify the investigated species by a 'position-frequency analysis' (PFA). After sorting the matrix of precipitate numbers in the ascertained optimal sequence of species, a cluster analysis was carried out. The phenogram showed 6 (respectively 8) group clusters. The members of the morphologic group I (Smith et al., 1952) was found only in group cluster 2. The phenogram was partly in agreement with phenograms based on other characteristics, e.g. DNA hybridization.

Represent the batches 2 of strain NCTC 3991 and NCTC 3992 B. coagulans?

In a previous publication (M. Hartung and E. Hellmann: Examination of 20 Bacillus Species by Crossed Immunoelectrophoresis under Taxonomic Aspects, Zbl. Bakt. Hyg. A 263 (1987) 509-524) we came to the conclusion that the species B. subtilis and B. coagulans were closely related. This statement has to be revised: The antigenic relationship is low. Further investigations have shown that all three B. coagulans-strains, although originating from different sources, were overgrown by B. subtilis. The same fact may have caused errors in other publications (e.g. Parry et al.: A Colour Atlas of Bacillus Species, Wolfe Medical Publications Ltd., London, 1983.

Nucleolus, nucleolar chromosomes, and nucleolus-associated chromatin from early diplotene to dictyotene in the human oocyte

The shape, relationships, relative DNA content, and nucleolar activity of the short arm of acrocentric bivalents were studied in human oocytes from early diplotene to dictyotene. At the beginning of diplotene, the short arms of the previously paired chromosomes were again separated and displayed the same morphological features as in mitotic prophase chromosomes. They were connected only with the nucleolus. In situ hybridization and silver staining showed that the nucleolar organizer regions (NORs) were located in the peripheral region of the nucleolus. Tritiated-uridine incorporation was active. At birth, the relationships of the acrocentric short arms showed increasing complexity. The chromosomes ended in nucleolus-associated chromatin blocks of irregular shape, containing large quantities of DNA as demonstrated by intense binding of 3H-actinomycin D. The number of chromosomes converging on these chromatin blocks exceeded the number of acrocentrics, suggesting that heterochromatic regions of other chromosomes were associated with the short arm of acrocentrics. In the electron microscope, the NORs were represented by fibrillar centers located on the periphery of the nucleolus and consistently connected with the blocks of dense chromatin. These relationships remained unchanged in the primordial oocyte in the adult ovary. Persistence of 3H-uridine uptake showed that the oocyte was not at a "resting" stage. The possible cytogenetic consequences of these observations are discussed.

Random acrocentric bivalent associations in human pachytene spermatocytes. Molecular implications in the occurrence of Robertsonian translocations

Acrocentric bivalent associations were studied in 232 human male germ cells at pachytene in order to understand better the preferential involvement of chromosomes 13, 14, and 21 in Robertsonian translocations. The tendency of each acrocentric bivalent to associate with another was not correlated with NOR activity, as measured by silver staining. Good agreement was noticed between their ability to associate and the amount of satellite DNA in human acrocentric chromosomes. The distribution of two-by-two acrocentric bivalent associations was random. In order to reconcile this result with the nonrandom distribution of Robertsonian translocations, a molecular hypothesis is proposed. The model is based on homology of recombinational sites, interspersed at regular interval in satellite DNA, which could increase the probability of accidental unequal crossing-over between two specific acrocentric chromosomes.

The association of the nucleolus and the short arm of acrocentric chromosomes with the XY pair in human spermatocytes: its possible role in facilitating sex-chromosome acrocentric translocations

Sex vesicle-nucleolus association was observed in 12% of zygotene and pachytene human spermatocytes using Giemsa and NOR-silver stained preparations. The silver-positive area of the nucleolus, corresponding to the nucleolus organizer (NOR), was usually close to the XY pair. C-banding frequently showed the terminal chromomere, formed by the condensed short arm of an acrocentric bivalent, attached to the sex vesicle. When a nucleolus produced by transcription of rDNA was connected to the short arm, it seemed to be secondarily associated with the sex vesicle. Non-transcribed ribosomal genes, which did not form a nucleolus, were revealed by in situ hybridization. Autoradiographs showed the rDNA-containing short arm of acrocentric bivalents associated with the sex vesicle in 18% of spermatocytes. The difference with the frequency of nucleolus-XY pair association was partially explained by the presence of inactive ribosomal genes. Moreover, electron microscopy showed that the dimensions of the newly formed nucleoli at early zygotene did not exceed 0.5 micron; they can be missed in light microscope investigations. From early zygotene to late pachytene, close relationships were observed between the sex vesicle chromatin and that of the associated acrocentric bivalent, especially in the short arm region. These relationships might explain the frequent involvement of acrocentrics in Y-autosome and X-autosome translocations occurring during male meiosis.

Distribution of fibrillar centers and silver-stained components in the nucleolus of human Sertoli cells

The nucleolus of the human Sertoli cell consistently showed three distinct, spontaneously segregated parts: 1. one or two large, silver-positive fibrillar centers; 2. strands of dense fibrillar component continuous with the dense cords surrounding the fibrillar center. These components were also silver-positive; 3. a granular, silver-negative mass. These observations show that in the human Sertoli cell the number of fibrillar centers is far lower than the diploid number of NORs. They also suggest that the fibrillar center might contain several NORs in this cell type.

Structural basis for Robertsonian translocations in man: association of ribosomal genes in the nucleolar fibrillar center in meiotic spermatocytes and oocytes

The spatial relationships of acrocentric chromosomes were studied during prophase I of meiosis in human oocytes and spermatocytes by using cytogenetic techniques, electron microscopy, and in situ hybridization. Ultrastructural investigations revealed an ordered arrangement of nucleolar bivalents at the zygotene and pachytene stages. The end of the bivalent corresponding to the cytological satellite was consistently attached to the nuclear envelope. The fibrillar center of the nucleolus always contained rDNA chromatin fibers emanating from the secondary constriction region. Association of ribosomal genes from two bivalents in the same fibrillar center was frequently observed. Ultrastructural studies demonstrated the close proximity of chromatids in the short arm region of the involved nonhomologous acrocentrics. A breakage/reunion model based on our data can explain the formation of all observed types of Robertsonian translocations: monocentrics and dicentrics with or without rDNA.

[Pulmonary fibrosis caused by hard-metal dusts]

Hardmetals are broadly used in many different branches. In the FRG lung fibrosis caused by hardmetal-dust are recognized as occupational diseases (no. 4107). New findings concerning pathogenesis of this disease should be considered. Not only the dust of the presintered material is hazardous but also the inhalation of the sintered material. There is a special risk for tool-grinders. Cobalt is suspected to be the causal agent. In tool-grinders an elevated external and internal Cobalt-burden has been objectified. We report about 14 persons who suffered from lung fibrosis and worked in the hard metal industry. X-ray and pathohistological examinations may give some hints but there is no specific histological correlate. So the notifying procedure may be difficult. For this reason any case of aetiologically unknown lung fibrosis the lung biopsy and quantitative chemical analysis using AAS should be performed. In one patient the Cobalt-level in lung-tissue was significantly elevated. Toleration of invasive diagnostic measurements can not be demanded. Tool-grinders need more medical surveillance in future. As a preventive strategy the cobalt-exposure is to be reduced to a minimum. The external cobalt-burden at work-place can be estimated by the determination of the renal Cobalt-excretion.

Association of centromeric heterochromatin with the nucleolus in mouse Sertoli cells

In adult Sertoli cells of most strains of mice, all the centromeric heterochromatin is condensed in two chromocenters, one on each side of a single, large nucleolus. In a random-bred Swiss OF-1 strain, however, the nucleus has a different structural organization. Part of the heterochromatin Is seen as chromocenters in contact with the nucleolus; the rest of it is dispersed in granules of unequal size in the nucleoplasm. Such an unusual spatial arrangement of heterochromatin in interphase nucleus cannot be explained either by a difference in the nucleolar organizing regions or by a polymorphism of the C-banding of metaphase chromosomes.

Nucleoli, micronucleoli, and nucleolus-like structures in human oocytes at meiotic prophase I studied by the silver-NOR technique

Meiotic nuclei preparations obtained from human fetal ovaries were studied with the silver-NOR technique. At leptotene, the NOR's were located at the periphery of the nucleoli. The mean number of NOR's per nucleus was 6.4. Moreover, 2-12 micronucleoli, each containing an Ag-positive zone, were observed. At pachytene, each nucleolus was divided into two zones, one of which was Ag-positive. The mean number of Ag-positive zones was 2.1 per nucleus. The subterminal region of the short arm of nucleolar bivalents was in contact with the argyrophilic nucleolar zone. In most cells, micronucleoli were dispersed between the bivalents. A single rounded body which stained heavily with silver was consistently observed. At early diplotene, the NOR's separated, appearing again as distinct rounded Ag-positive structures embedded in the peripheral part of the nucleoli. The silver-stained round body was still visible. Eight to twelve micronucleoli were observed. At a more advanced stage of diplotene, the number of micronucleoli increased, varying from 20 to 50 per nucleus. These observations suggest that the micronucleoli, already visible at the leptotene stage, are the morphological expression of an early transcription of amplified rDNA. The biological significance of the Ag-positive round body remains obscure, but the consistency of its appearance suggests that it has a specific function somehow related to nucleolar proteins.

On the question of the pathogenetic importance of cobalt for hard metal fibrosis of the lung

Pulmonary fibrosis in hard metal grinders has been observed to an increasing degree in recent years. Most authors attribute the cause of this disease to the influence of the cobalt contained in hard metals. The present case dealt with a 36-year-old man who had been exposed to the grinding dust from sintered hard metal parts for more than 10 years. Biopsy of the lung revealed an advanced, active pulmonary fibrosis. In the biopsy specimens cobalt was determined by flameless atomic absorption. The cobalt content in the biological specimens of the patient (urine: 7.5 micrograms/l; lung: 1010 micrograms/kg wet weight) was significantly increased compared with the values measured in normal controls.

Sex vesicle-associated nucleolar organizers in mouse spermatocytes: localization, structure, and function

Selective silver staining demonstrated that autosomal bivalents containing transcriptively active nucleolar organizers associated with the sex vesicle during pachytene of mouse spermatocytes. Later in pachytene, the nucleolar organizers covered the portion of the sex vesicle furthest from the attachment to the nuclear envelope. Hybridization in situ revealed the presence of rDNA in the silver-positive material. The nucleolus, formed from an autosomal bivalent, exhibited a large fibrillar center surrounded by an electron-opaque fibrillar zone. The nucleolar association with the sex vesicle was studied at early, middle, and late pachytene by hybridization in situ, NOR silver staining, and electron microscopy. These observations enabled us to further define the relationships of the nucleolar components with the X-Y pair.

Association of ribosomal genes in the fibrillar center of the nucleolus: a factor influencing translocation and nondisjunction in the human meiotic oocyte

Prophase I meiosis was studied in the human oocyte obtained from 16- to 24-week-old fetuses. Electron microscopy and silver stainihg showed that, at pachytene, the ribosomal genes belonging to several chromosomes are gathered in the same nucleolar fibrillar center, where they are embedded in an argyrophilic protein. The nucleolus showed spontaneous segregation of its components due to temporary inactivation of the ribosomal genes. The fibrillar center, separated from the other nucleolar components, was penetrated as midpachytene by chromatin fibers containing rDNA emanating from one to three nucleolar bivalents. Thus, the ribosomal genes from 4-12 chromatids are temporarily juxtaposed inside the same structure. Such a structural arrangement is completely different from that observed in the pachytene-stage mouse oocyte, where two independent and active nucleoli, each displaying its own fibrillar center, were formed on the bivalents containing paired ribosomal genes. These different structural patterns are correlated with the high frequency of nondisjunction in the human oocyte and the relative infrequency of such in the mouse oocyte. The pattern observed in the human oocyte may be a cause of translocations.