Cytology of spore formation in Clostridium perfringens

Distribution of Enterotoxin- and Epsilon-Positive Clostridium perfringens Spores in U.S. Retail Spices

The role of spices as vehicles of foodborne illness prompted an examination of bacterial spores in these products. Here, we report on the levels and characteristics of spores of Clostridium perfringens associated with 247 U.S. retail spices. Forty-three confirmed isolates from 17% of samples were obtained, present at levels ranging from 3.6 to 2,400/g. Twenty-seven (63%) of C. perfringens isolates were positive for the enterotoxin gene ( cpe). Seven random spice isolates produced enterotoxin at levels of between 4 and 16 ng/mL, compared with three outbreak (control) strains that each produced enterotoxin levels of >1,024 ng/mL. D_95°C levels (1.0 to 3.3 min) of spores of four randomly selected spice isolates suggests a plasmid-localized cpe, while one had D_95°C (>45 min) consistent with chromosomally located cpe. Five of the 43 isolates possessed the epsilon toxin gene ( etx, as well as cpe). Foods could easily become contaminated with spores of cpe-positive C. perfringens by the addition of spices. Because of its spore-forming ability, its rapid generation times at elevated temperatures, improper heating, cooling, and holding conditions could lead to elevated levels of C. perfringens in foods, a requirement for its implication in foodborne outbreaks.

Structure, assembly, and function of the spore surface layers

Endospores formed by Bacillus, Clostridia, and related genera are encased in a protein shell called the coat. In many species, including B. subtilis, the coat is the outermost spore structure, and in other species, such as the pathogenic organisms B. anthracis and B. cereus, the spore is encased in an additional layer called the exosporium. Both the coat and the exosporium have roles in protection of the spore and in its environmental interactions. Assembly of both structures is a function of the mother cell, one of two cellular compartments of the developing sporangium. Studies in B. subtilis have revealed that the timing of coat protein production, the guiding role of a small group of morphogenetic proteins, and several types of posttranslational modifications are essential for the fidelity of the assembly process. Assembly of the exosporium requires a set of novel proteins as well as homologues of proteins found in the outermost layers of the coat and of some of the coat morphogenetic factors, suggesting that the exosporium is a more specialized structure of a multifunctional coat. These and other insights into the molecular details of spore surface morphogenesis provide avenues for exploitation of the spore surface layers in applications for biotechnology and medicine.

Influence of pH extremes on sporulation and ultrastructure of Sarcina ventriculi

Distinct morphological changes in the ultrastructure of Sarcina ventriculi were observed when cells were grown in medium of constant composition at pH extremes of 3.0 and 8.0. Transmission electron microscopy revealed that at low pH (less than or equal to 3.0) the cells formed regular packets and cell division was uniform. When the pH was increased (to greater than or equal to 7.0), the cells became larger and cell division resulted in irregular cells that varied in shape and size. Sporulation occurred at high pH (i.e., greater than or equal to 8.0). The sporulation cycle followed the conventional sequence of development for refractile endospores, with the appearance of a cortex and multiple wall layers. The spores were resistant to oxygen, lysozyme, or heating at 90 degrees C for 15 min. Spores germinated within the pH range of 4.6 to 7.0.

Ultrastructural changes during encystment and germination of Bdellovibrio sp

Under proper conditions, Bdellovibrio sp. strain W cells develop into bdellocysts in appropriate prey bacteria. After attachment and penetration of the prey cell, the encysting bdellovibrio began to accumulate inclusion material and increase in size, and was surrounded by an outer layer of amorphous electrondense material. The cytoplasm of the encysting cell appeared more electron dense, and nuclear areas appeared more compact. During germination of bdellocysts, the outer wall was uniformly broken down the inclusion material changed shape and affinity for the heavy metal stain, and the nuclear areas expanded. As the outer wall was dissolved, outgrowth began with the elongation of the germinant as it emerged from the prey ghost as an actively motile cell.

Properties of Bacillus cereus spore coat mutants

Two classes of spore mutants have been selected in Bacillus cereus T, those producing lysozyme-sensitive spores, and those producing spores dependent upon lysozyme for germination. One mutant from each class was studied in detail and found to have defective packing of the spore coat layers. The major spore coat poplypeptide appeared to be altered on the basis of gel electrophoretic profiles and/or peptide maps of half-syctine-containing peptides. The spores of the mutants of both classes were sensitive to lysozyme and failed to respond to the germinants L-alanine plus adenosine. The spores were also more sensitive to octanol than the parental strain, but contained the same amount of dipicolinic acid and were equally heat resistant. The reversion frequencies in both cases were consistent with an initial point mutation, suggesting that an alteration in the major coat polypeptide accounted for the phenotypic properties studied.

Exosporium and spore coat formation in Bacillus cereus T

The exosporium of Bacillus cereus T was first observed as a small lamella in the cytoplasm in proximity to the outer forespore membrane (OFSM) near the middle of the sporangium. Serial sections, various staining methods, and enzyme treatments failed to show any connections between the small lamella and the OFSM. The advancing edge of the exosporium moved toward the polar end of the cell until the spore was completely enveloped. The middle coat was formed between the exosporium and the OFSM from a three-layered single plate or "belt," consisting of two electron-dense layers separated by an electron-transparent layer. This "belt," usually first observed toward the center of the sporangium, developed without changing thickness or appearance over the surface of the forespore. Between the middle coat and the OFSM, a layer of cytoplasm about 50-nm thick was enclosed by the developing coat; this became the inner coat. Electron-dense material was deposited on the outer surface of the middle coat to form the outer coat.

Responses of indigenous microorganisms to soil incubation as viewed by transmission electron microscopy of cell thin sections

Air-dried soils were adjusted to 50% moisture-holding capacity and incubated for 2 weeks at 30 C. Samples were removed at intervals, and their total microbial populations were physically separated and concentrated from the soil debris for sectioning and ultrastructure examination. Although the total numbers of cell sections in these preparations remained relatively constant during the soil incubations, the percentages of dwarf cells (</=0.3 mum in diameter), minute cells (</=0.2 mum in diameter), and cells with a cystlike structure decreased with time followed by a slow increase. During this period, a corresponding increase and decrease occurred in the percentages of cells in the 0.3- to 0.5-mum diameter range, but dividing cells were rarely observed. The percentages of spores and of cells with electron-transparent areas also increased and then decreased during incubation. When nutrients were added to these soils, the initial increases in cell size occurred at what appeared to be a faster rate. But this probably was related to a corresponding increase in total cell numbers which also occurred. The responses of the spores, cystlike cells, and cells with electron-transparent areas to nutrient additions were not consistent although all conditions of incubation, regardless of nutrient addition, increased the occurrence of an enlarged diffuse intine-like layer for the cystlike cells. In addition to the above, incubated soils contained cells, which were mainly in the 0.3- to 0.5-mum cell diameter range, that had an internal membrane surrounding the general area of the nuclear material. Changes in additional fine structure features of the microbial populations are described.

Exosporium formation in sporulating cells of Clostridium botulinum 78A

In sporulating cells of Clostridium botulinum type A (NCA strain 78A), formation of exosporia was initiated laterally in the sporangia before the synthesis of the spore cortex. Mature spores were enveloped by multilayered exosporia; the layers were uniform in appearance, approximately 3 nm thick, with a center-to-center distance of 7 nm.

Isolation and properties of mesosomal membrane fractions from Micrococcus lysodeikticus

1. A method is described for the isolation of pure mesosomal membrane fractions from Micrococcus lysodeikticus. 2. Plasmolysis of cells, before wall digestion, was necessary for effective mesosome release. 3. The effect of mild shearing forces, temperature and time upon the release of mesosomal membrane from protoplasts was investigated. 4. The optimum yield of mesosomal membranes from stable protoplasts was achieved at 10mm-Mg(2+). 5. Mesosomal membrane vesicle fractions prepared at differing Mg(2+) concentrations above 10mm were similar in chemical composition. 6. Comparison of the properties of peripheral and mesosomal membrane fractions revealed major differences in the distribution of protein components, membrane phosphorus, mannose and dehydrogenase activities between the two fractions. 7. Only cytochrome b(556) was detected in mesosomal membranes, whereas peripheral membranes contained a full complement of cytochromes. 8. Preliminary investigations suggested the localization of an autolytic enzyme(s) in the mesosomal vesicles. 9. The anatomy of mesosomal and peripheral membrane have been compared by the negative-staining and freeze-fracture technique. 10. The results are discussed in relation to a plausible role for the mesosome.

Interference-contrast and phase-contrast microscopy of sporulation in clostridium thermosaccharolyticum grown under strict anaerobiosis

Cells of Clostridium thermosaccharolyticum grown under strict anaerobiosis (modified Hungate technique) were examined during growth and sporulation by employing Nomarski interference-contrast and Zernike phase-contrast optics to delineate the sequence of morphological changes leading to the formation of free, mature spores. A 0.5% l-arabinose, liquid, complex medium was used to obtain a yield of 30 to 40% free, refractile spores (ca. 10(8)/ml) by 48 hr of incubation. The mean doubling time for the glucose culture (vegetative cells) was found to be 80 min, and that for the l-arabinose culture (sporulating cells), 498 min. By 8 hr of incubation, beginning spore formation became evident in the arabinose culture by the development of a distinct arrowhead-shaped terminal swelling. By 32 hr of incubation or shortly thereafter, Nomarski optics showed the mature spore to be uniformly spherical, whereas the enlarged terminal swelling containing it was not. The use of phase-contrast and interference-contrast optics permitted the characterization of the distinctive morphological changes occurring during sporulation of C. thermosaccharolyticum.

Sporulation and enterotoxin production by mutants of Clostridium perfringens

The ability of Clostridium perfringens type A to produce an enterotoxin active in human food poisoning has been shown to be directly related to the ability of the organism to sporulate. Enterotoxin was produced only in a sporulation medium and not in a growth medium in which sporulation was repressed. Mutants with an altered ability to sporulate were isolated from an sp(+) ent(+) strain either as spontaneous mutants or after mutagenesis with acridine orange or nitrosoguanidine. All sp(0) (-) mutants were ent(-). Except for one isolate, these mutants were not disturbed in other toxic functions characteristic of the wild type and unrelated to sporulation. A total of four of seven osp(0) mutants retained the ability to produce detectable levels of enterotoxin. None of the ent(-) mutants produced gene products serologically homologous to enterotoxin. A total of three sp(-) mutants, blocked at intermediate stages of sporulation, produced enterotoxin. Of these mutants, one was blocked at stage III, one probably at late stage IV, and one probably at stage V. A total of three sp(+) revertants isolated from an sp(-) ent(-) mutant regained not only the ability to sporulate but also the ability to produce enterotoxin. The enterotoxin appears to be a sporulation-specific gene product; however, the function of the enterotoxin in sporulation is unknown.

Spore fine structure in Clostridium cochlearium

The fine structure of Clostridium cochlearium was examined by use of thin sections, negative stains, and carbon replicas. Particular attention was given to details of the sporulation process and to fine structure of the spores. Spore coat formation was well advanced before the first evidence of cortex formation was noted. Three distinct spore coats were detected, the outermost of which was composed of seven layers. In addition, the spores possessed tubular appendages of variable length attached to one end of the spore. These differed in a number of respects from those described for other clostridia.

Scanning electron and phase-contrast microscopy of bacterial spores

The three-dimensional immages of free and intrasporangial spores produced by scanning electron microscopy show surface structures not visible by phase-contrast microscopy. Although fine surface detail is not elucidated by scanning electron microscopy, this technique does afford a definitive picture of the general shape of spores. Spores of Bacillus popilliae, B. lentimorbus, B. thuringiensis, B. alvei, B. cereus, and Sarcina ureae have varying patterns of surface ridge formation, whereas spores of B. larvae, B. subtilis, and B. licheniformis have relatively smooth surfaces.

Cytology of spore germination in Clostridium pectinovorum

The process of spore germination in Clostridium pectinovorum has been followed by phase-contrast and electron microscopy. Unlike most other Bacillaceae, germination of this species takes place within the sporangium. Under phase-contrast, the spore darkens and swells slightly, and then the vegetative rod slips out through the end opposite the collar-like extension of the sporangium. In thin sections, a spore from an early stage in germination consists of a central protoplast, core membrane, germ cell wall, cortex, and two coats. Within a short period, the cortex disintegrates and the young cell develops. It possesses a large fibrillar nucleoplasm and several mesosomes. Subsequently, the young cell elongates, becomes somewhat deformed, and then emerges through a narrow aperture in the inflexible coats of the spore, finally rupturing the sporangium. Free vegetative cells of C. pectinovorum resemble in their structure other gram-positive rods.