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P GERHARDT

Publications and source records attributed to P GERHARDT.

At least 19 recordsLinked to original sources
PubMed1964

POROSITY OF ISOLATED CELL WALLS OF SACCHAROMYCES CEREVISIAE AND BACILLUS MEGATERIUM.

Gerhardt, Philipp (The University of Michigan, Ann Arbor), and Jean A. Judge. Porosity of isolated cell walls of a yeast and a bacillus. J. Bacteriol. 87:945-951. 1964.-Decagram masses of cell walls were isolated from Saccharomyces cerevisiae and Bacillus megaterium; their porosity was examined by measuring the extent of uptake with polyethylene glycols and dextrans varying in molecular weight from 62 to 2,000,000. The results indicated that both walls are heteroporous. The near equality of extrapolated water-uptake values and determined moisture contents suggested that water in the cell walls is mainly free for distribution of solutes. Polymers with molecular weights of 4,500 and above were excluded by the yeast walls, and those with molecular weights of 57,000 were excluded by the bacillus walls; from these results, maximal openings of 36 and 107 A, respectively, were calculated. Electron micrographs of shadowed, stained, and sectioned walls revealed fine structure not inconsistent with heteroporosity, but the predicted openings were not seen. Altogether, in structure and permeability behavior, the cell walls were like a random meshwork of cross-linked macromolecular strands.

Bacillus↗
PubMed1964

ULTRASTRUCTURE OF THE EXOSPORIUM ENVELOPING SPORES OF BACILLUS CEREUS.

Gerhardt, Philipp (The University of Michigan, Ann Arbor), and Edgar Ribi. Ultrastructure of the exosporium enveloping spores of Bacillus cereus. J. Bacteriol. 88:1774-1789. 1964.-Structural details in the outer envelope of spores, such as those of Bacillus cereus and B. anthracis, were studied by electron microscopy and by X-ray diffraction analysis. Procedures were developed for isolating homogeneous fragments of the membrane with minimal damage to or germination of the spore proper. Exosporium of B. cereus appeared to embody two main layers. An outer layer was made up of a nap of hairlike projections, irregularly distributed and about 250 A deep; these arose from an intermediate covering, about 60 A in depth and similarly lead-stainable. An inner basal layer had a hexagonally perforate surface pattern of holes, averaging 76 A from center to center, and was made up of four lamellae, which could fragment into crystal-like elements. The intact basal membrane was about 190 A thick and the thinnest elements, 45 A. Microscopic observations of a crystal-like nature of the exosporium basal membrane were confirmed by X-ray diffraction analysis; the pattern of reflection lines in powder diagrams of exosporium fragments or paracrystals, or intact spores, corresponded to a hexagonal, close-packed crystal structure. The unit cell was calculated to have dimensions of 7.6 A along the a axis and 11.9 A along the c axis of the space lattice.

Bacillus anthracis↗
PubMed1963

DIALYSIS FLASK FOR CONCENTRATED CULTURE OF MICROORGANISMS.

Gerhardt, Philipp (The University of Michigan, Ann Arbor), and D. M. Gallup. Dialysis flask for concentrated culture of microorganisms. J. Bacteriol 86:919-929. 1963.-A twin-chambered dialysis flask was designed with a supported membrane clamped between a reservoir of medium in the bottom and a small volume of culture above, the unit being mounted on a shaking machine to provide aeration and agitation. The performance of different dialysis membranes and membrane filters was compared in glucose-diffusion and bacterial-culture tests. Some of the variables in dialysis culture were assessed and the growth response was characterized, with Serratia marcescens as the test organism. The general usefulness and concentrating effect of dialysis culture were demonstrated in trials with 16 representative types of microorganisms. Dialysis culture was shown to be especially suitable for producing dense populations of cells or their macromolecular products in an environment free from complex medium constituents, for removing toxic products that limit growth or fermentation, and for supplying oxygen by diffusion without the damage from usual aeration procedures.

Bacteriological Techniques↗
PubMed1962

Permeability of bacterial spores. III. Permeation relative to germination.

Black, S. H. (The University of Michigan, Ann Arbor) and Philipp Gerhardt. Permeability of bacterial spores. III. Permeation relative to germination. J. Bacteriol. 83:301-308. 1962.-The passive diffusion of solutes into dormant spores, characterized previously with the test organism Bacillus cereus strain terminalis, has now been examined in relation to germination. Dormant spores did not take up specific germinants differently than they did other compounds, under conditions optimal for germination. Germinated spores, viable but prevented from growing out, displayed some changes in permeability, evidenced by increased total uptake of glucose and water and by observable penetration of a fluorescigenic dye. Heat-killed spores were as permeable to glucose and the dye as germinated ones.

Bacillus cereus↗
PubMed1962

Permeability of bacterial spores. IV. Water content, uptake, and distribution.

Black, S. H. (The University of Michigan, Ann Arbor) and Philipp Gerhardt. Permeability of bacterial spores. IV. Water content, uptake, and distribution. J. Bacteriol. 83:960-967. 1962.-Dormant and germinated spores of Bacillus cereus strain terminalis were examined for water properties. Respectively, they exhibited a mean density of 1.28 and 1.11 g/ml, a water content of 64.8 and 73.0%, and a total water uptake of 66.6 and 75.6%, based on spore weight, or 86.0 and 83.9%, based on spore volume. The results confirmed a previous report that internal and external water are in virtually complete equilibrium, but refuted a prevailing hypothesis that heat resistance is attributable to a dry core. A model of spore ultrastructure that evolved from the cumulative results pictures a moist, dense, heteroporous core. A new hypothesis is formulated as an explanation for thermostability in spores and possibly in other instances; it postulates the occurrence of an insolubly gelled core with cross-linking between macromolecules through stable but reversible bonds so as to form a high-polymer matrix with entrapped free water.

Bacillus↗
PubMed1961

Permeability of bacterial spores. I. Characterization of glucose uptake.

Black, S. H. (The University of Michigan, Ann Arbor) and Philipp Gerhardt. Permeability of bacterial spores. I. Characterization of glucose uptake. J. Bacteriol. 82:743-749. 1961.-The total uptake of glucose by masses of clean, dormant spores was measured to assess their permeability. After correction for intercellular space, packed spores of Bacillus cereus strain terminalis were found in 87 determinations to be permeated by glucose to 40% of their weight. The glucose uptake was relatively independent of environmental variables, and thus was concluded to occur principally through a process of passive diffusion.

Bacillus↗
PubMed1961

Permeability of bacterial spores. II. Molecular variables affecting solute permeation.

Gerhardt, Philipp (University of Michigan, Ann Arbor) and S. H. Black. Permeability of bacterial spores. II. Molecular variables affecting solute permeation. J. Bacteriol. 82:750-760. 1961.-More than 100 compounds were tested for their uptake by dormant spores of a bacillus. The extent of penetration was found to be dependent on at least three molecular properties: (i) The dissociation of electrolytes usually resulted in high or low uptake predictable from their charge. (ii) Lipid insolubility restricted permeation of small molecules. (iii) The molecular weight of unsubstituted glycol and sugar polymers exponentially limited penetration to eventual exclusion at mol wt above 160,000. The results were plotted as a generalized curve, calculations from which permitted an interpretation that the effective spore surface contains pores varying in diameter from 10 to 200 A.

Bacillus↗
PubMed1960

Studies on the fine structure of microorganisms. V. Morphogenesis of nuclear and membrane structures during ascospore formation in yeast.

The fine structure of cells of Saccharomyces cerevisiae engaged in the formation of ascospores was studied in electron micrographs of ultrathin sections. Although the mode of the first reduction division could not be clearly determined, the second nuclear division appeared to proceed in a manner similar to that observed previously during vegetative division. That is, division by constriction of the existing nucleus occurs without dissolution of the nuclear membrane and without involvement of discrete chromosomes. Variously shaped areas of low electron density were discerned within the nucleoplasm; these had not been previously seen in the vegetative nucleus. The significance of this nuclear differentiation and its possible similarity to nuclear structures reported in bacteria and an imperfect fungus are discussed. The cytoplasmic membrane appears first in the developing ascospore. The formation of an outer coat and an inner coat then follows. The cytoplasmic vacuole was observed not to be incorporated into the spore. An unusual intracytoplasmic membrane was observed in the spore and appeared to be at least temporarily continuous with the nuclear membrane.

Cell Membrane↗