Die Fimbrien von Rhizobium lupini 1/50, sta-

Zusammenfassung Die Fimbrien (oder Pili) einer nicht sternbildenden Mutante (1–50, sta^-) von Rhizobium lupini wurden elektronenmikroskopisch untersucht. Die Fimbien sind peritrich an der Bakterienzelle inseriert, und zwar während der exponentiellen Wachstumsphase meist einzeln. In der stationären Phase nehmen die Fimbrien an Zahl und Länge kontinuierlich stark zu; sie sind dann häufig büschelweise inseriert. Zusammen mit den oft zopfbildenden Geißeln verflechten sie sich zu einem ausgedehnten Netzwerk. Die Aneinanderlagerung der Fimbrien erfolgt unspezifisch durch Kohäsion; durch ebenfalls unspezifische Adhäsion haften sie auf dem Substrat.Die Fimbrien haben ca. 30 Å Durchmesser und sind röhrenförmig gebaut. Ihre lichte Weite beträgt 8 bis 10 Å. Ein allgemeines Bauschema der Fimbrien wird diskutiert. In der Diskussion über die allgemeine Funktion aller Arten von Fimbrien wird ihre Haftfähigkeit herausgestellt. Die Fimbrien der Mutante 1/50, sta^- sind wegen ihres geringen Innendurchmessers nicht als Transportröhren für doppelsträngige DNS und wahrscheinlich auch nicht für einzelsträngige DNS oder RNS geeignet.

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The fimbriae of Rhizobium lupini 1/50, sta^-

Summary The fimbriae (pili) of a non-starforming mutant (1/50, sta^-) of Rhizobium lupini were studied under the electron microscope. In the exponential phase of growth, fimbriae are singly, peritrichously inserted. During stationary growth these fimbriae increase by number and length. Together with the larger flagella they often form an extended reticulum. The fimbriae often stick together by unspecific cohesion forces; their attachment to the substrate can be explained by unspecific adhesion.The outer diameter of the fimbriae is 30 Å, the inner diameter 8 to 10 Å.The tubelike structure of fimbriae (pili) is discussed in terms of a general model.The most obvious general function of all types of fimbriae is their connecting power.The inner dimension of the fimbriae of the 1/50, sta^-—mutant exclude a model where they function as transport tubes for double-stranded DNA and probably for single stranded DNA or RNA either.

     

Microbodies (peroxisomes) in the toad,Bufo marinus

Summary Microbodies (peroxisomes), a group of cytoplasmic organelles enriched in catalase, are demonstrated in the toad, Bufo marinus, by light and electron microscopy by means of a cytochemical staining procedure that demonstrates the peroxidatic activity of catalase with diaminobenzidine (DAB). Amphibian microbodies are similar to those of other classes in their fine structure and localization in hepatocytes and kidney, where they are prominent in the proximal tubular cells. Nucleoids are present only in renal microbodies. In the proximal renal tubule an unusual group of large brown granules are identified as lysosomes by their acid phosphatase, -glucosaminidase and -glucuronidase activities.This work was supported by U.S. Public Health Service Grants Nos. NS-06856 and HD 00674. We wish to thank Dr. Richard M. Hays who generously supplied us with toads; Dr. Alex B. Novikoff for making available facilities for ultramicrotomy, Miss Betty De Prest for technical assistance; Miss Marianne Van Hooren for preparation of the photomicrographs.     

Microbiological Deterioration of Frozen Parfried Potatoes upon Holding After Thawing

Frozen parfried potatoes were thawed and stored at 55, 45, and 34 F (12.8, 7.2, 1.1 C). Significant changes in flavor and texture did not occur at these temperatures until the total bacterial count exceeded 100 million per gram. These sensory changes were produced after 4, 8, and 20 days of storage at 55, 45, and 34 F, respectively. Detectable color change appeared sooner and probably was not of microbial origin. It is unlikely that any health hazard exists under the range of conditions studied. Nevertheless, it seems undesirable to market food with such a high bacterial count. At half the storage periods given above, the count did not exceed 100,000 per gram.     

Studies of animal populations from Lamarck to Darwin

Summary and conclusions Darwin's theory of evolution brought to an end the static view of nature. It was no longer possible to think of species as immortal, with secure places in nature. Fluctuation of population could no longer be thought of as occurring within definite limits which had been set at the time of creation. Nor was it any longer possible to generalize from the differential reproductive potentials, or from a few cases of mutualism between species, that everything in nature was fitted to produce general ends, and reciprocal uses. ¹³⁴ The appeal to design could no longer be substituted for answers to questions concerning animal demography. Instead, the dynamics of a population had to be viewed as the outcome of species' struggle against animate and inanimate factors in the environment. Both the members of a species and the environmental factors tend to vary randomly, and therefore neither evolution nor population dynamics could be fully understood alone. For this reason Darwin's linking of the two subjects was inevitable and not merely an historical accident. Since Darwin had shown that no automatic equilibrium existed, he demonstrated the importance of closer study of the causes of population dynamics and extinction. He also indicated that an understanding of population depends upon the development of a broad knowledge in ecology.Viewed from another direction, Darwin's work ended the early modern era of population studies by clarifying three interrelated problems which were important for understanding population: extinction, distribution, and the nature of species. The components of his answer had been discussed in the eighteenth century, but there had not existed enough evidence for the completion of the revolution in thought which had then begun. At the beginning of the nineteenth century, Playfair found the evidence for extinction conclusive, and, in spite of Lamarck, Curvier convinced the scientific world that there could no longer be any doubt about it. This was a step the importance of which, with his limited knowledge of biogeography and population, Cuvier could not have fully realized. Lamarck attempted, with his evolutionary theory, to circumvent the necessity for admitting extinction, but he overestimated the adaptability of organisms and in doing so he underestimated the importance of competition and the whole field of ecology. On the other hand, he was not willing to let questions such as the origin of species remain taboo to science. The origin of species was a biogeographical as well as a paleontological question. Humboldt correlated environment with the distribution of species and conveyed the impression that plant communities are subject to change. De Candolle, following the lead of Linnaeus and Humboldt, emphasized the ecological aspects of biogeography, not only the importance of habitat and range, clearly showing the ecological effects of competition. The entomologists Kirby and Spence took a faltering step toward understanding the relationship between population and ecological role, but they fell short of any significant new conclusions. Neither they nor Swainson could fully comprehend the new perspective of De Candolle.Lyell was able to bring together the evidence from these three lines of investigation and weave them into an important synthesis that almost accomplished that Darwin later did. Although opposing Lamarck's theory of evolution, Lyell had a dynamic view of ecology. He realized that population dynamics offered an important key to the understanding of biogeography. Since he knew that species become extinct, he investigated closely the factors which could either preserve or extinguish species. While explaining these factors, he described the interrelationships of species in greater detail than had ever been done before. Forbes continued to develop Lyell's ecological concepts, and his first-hand field experience enabled him to describe biotic communities more concretely than Lyell had.Having the advantages of Lyell's understanding and his own experience from a global voyage, Darwin could take the final step from the static to the dynamic concept of life. He had seen populations fluctuating and also fossil species in South America, and on the Galapagos Islands he had encountered a biogeographical problem that could not be credibly solved without the idea of evolution. However, the bare idea of evolution did not fully answer his questions. He sought physiological causes of extinction before he read Malthus and realized that De Candolle and Lyell had correctly emphasized the importance of competition. Darwin found that, in order to understand evolution, he needed to improve his understanding of ecology. He wanted to know when populations were most easily decimated, how extensive were competition and cooperation, what effects parasites have upon populations, and what changes occur in biotic communities when a species is either added or subtracted. He contributed to some extent to answering these questions. Though there remained much for others to do, there was now a new and more secure theoretical framework within which later studies could be interpreted. As Ernst Mayr has observed, Darwin's consistent thinking in terms of population has had an impact on biological theory and practice which is second only to his sponsorship of natural selection as the mechanism of evolution. ¹³⁵     

Formation of Extracellular Sphingolipids by Microorganisms: IV. Pilot-Plant Production of Tetraacetylphytosphingosine by Hansenula ciferrii

Tetraacetylphytosphingosine (TAPS) formation by the F-60-10 mating type strain of the yeast Hansenula ciferrii, previously observed on agar plates, has been shown to take place in submerged cultures. The optimal conditions for TAPS formation, and the correlation of TAPS production and sugar utilization under aerobic conditions, were studied in 10-liter fermentors. For each gram of glucose consumed, 5 mg of TAPS were formed; for each gram of yeast solids produced, 15 mg of TAPS were synthesized. A 750-liter pilot-plant run yielded 175 g of crude TAPS, which were obtained by hexane extraction of centrifuged yeast cells.     

POLYESTER-METHACRYLATE EMBEDMENTS FOR ELECTRON MICROSCOPY

It has been found that tissues fixed for electron microscopy and dehydrated in acetone can be embedded in mixtures of n-butyl methacrylate and polyester resin. Activation with 1 per cent tert-butyl hydroperoxide followed by 12 to 48 hours at 60°C produces blocks that section well with glass knives. The ribbons are cleared of methacrylate by heat (200–250°C for 1 hour) and/or immersion in organic solvents (CCL₄, acetone-ether). After removal of the methacrylate the residual polyester matrix provides thermostable and insoluble support for the tissue. Its insolubility permits staining by immersion of cleared preparations in organic solvents carrying heavy metal compounds in solution. Clearing by heat stabilizes section-grid relationships. The removal of volatile materials by clearing substantially reduces contamination of both specimen and microscope. Tissue fine structure is well preserved in these preparations.