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G D SHOCKMAN

Publications and source records attributed to G D SHOCKMAN.

18 recordsLinked to original sources
PubMed1963

Protoplast membrane of Streptococcus faecalis.

Shockman, Gerald D. (Temple University School of Medicine, Philadelphia, Pa.), Joseph J. Kolb, Bohdan Bakay, Margaret J. Conover, and Gerrit Toennies. Protoplast membrane of Streptococcus faecalis. J. Bacteriol. 85:168-176. 1963.-The membrane fraction of Streptococcus faecalis (ATCC 9790) was isolated and purified, by a variety of procedures, from cultures that were grown under closely controlled conditions of physiological age and nutrition. The most satisfactory method required the use of lysozyme-to-cell ratios below 0.01 and the intermediate formation of protoplasts in osmotically protective media. Amino acid analyses of three of the membrane preparations indicated a characteristic and constant, but not unusual, pattern; 42% of the membranes from threonine-depleted and 49 to 55% of the membranes from log-phase cultures were accounted for as protein. Significant quantities of d-alanine or d-aspartic acid were not detected, indicating the absence of contaminating cell-wall substance. Essentially, all of the nitrogen was accounted for as amino acids. The lipid content of membranes from stationary-phase threonine-depleted (36%) and valine-depleted (40%) cultures was significantly higher than the corresponding fraction of exponential-phase cultures (28%). The phosphorus content of the membrane lipid was relatively constant (2.8 to 3.0%), and the nitrogen content was extremely low (0.12 to 0.26%). Thus, changes in the composition of the membrane fraction occurred during the transition of log-phase cells into threonine- or valine-depleted cells.

Alanine↗
PubMed1962

Inhibition by antibiotics of the growth of bacterial and yeast protoplasts.

Shockman, Gerald D. (Temple University School of Medicine, Philadelphia, Pa.) and J. Oliver Lampen. Inhibition by antibiotics of the growth of bacterial and yeast protoplasts. J. Bacteriol. 84:508-512. 1962.-The characteristics and requirements for growth of bacterial (Streptococcus faecalis) and yeast (Saccharomyces cerevisiae) protoplasts were established and the effect of a variety of antibacterial and antifungal antibiotics determined. A clear differentiation was obtained between such inhibitors of bacterial cell wall synthesis as penicillin and cycloserine, which did not prevent protoplast growth, and all others, antibacterial and antifungal, which inhibited protoplasts and intact organisms at the same range of concentration. Novobiocin, previously reported to inhibit bacterial wall synthesis, was also effective against a reaction(s) essential to the growth of S. faecalis protoplasts. The antibacterial action of streptomycin, neomycin, and kanamycin was essentially eliminated by the high salt concentration needed to maintain the protoplasts. Removal of the cell wall did not significantly increase antibiotic susceptibility of a resistant species. Protoplasts of Bacillus megaterium were insensitive to the antifungal agent, nystatin, and did not bind it to any detectable degree. Thus, the yeast or bacterial cell wall does not appear to play a major role in determining relative antibiotic susceptibility by masking internal sensitive target sites. A variety of antifungal antibiotics tested on the growth of log-phase yeast cells failed to produce osmotically fragile forms.

Anti-Bacterial Agents↗
PubMed1961

Cell multiplication studied with an electronic particle counter.

Toennies, G. (Institute for Cancer Research, Philadelphia, Pa.), L. Iszard, N. B. Rogers, and G. D. Shockman. Cell multiplication studied with an electronic particle counter. J. Bacteriol. 82:857-866. 1961.-Suitable conditions are described for the application of the Counter electronic particle counter to the study of bacterial number and particle size distribution in growing cultures. When Streptococcus faecalis and Escherichia coli were each grown in a different medium, exponential growth was accompanied by a continuous decrease in average particle size. The average apparent particle volume of S. faecalis decreased by about 50% in five generations. Microscopic studies of S. faecalis indicated that this was due to a decrease in the average chain length of the cultures. The following observations concerning average particle size during exponential growth of S. faecalis in a synthetic medium were made: (i) A decreased concentration of tryptophan, serine, or proline resulted in a significant decrease in average particle size. Similar changes in numerous other nutrients produced no or only minor changes. (ii) The addition of a cytoplasmic extract prepared from exponentially growing cells resulted in changes similar to those resulting from the partial withdrawal from the medium of certain nutrients. (iii) The effect of the cytoplasmic extract could be counteracted by the addition of tryptophan. (iv) A limited survey, including the effects of the rate of exponential growth, mechanical agitation, the presence of indoleacetic acid, indole, kinetin, lysozyme, or ascorbate, disclosed no additional factor which significantly influenced the particle size distribution.

Bacteriological Techniques↗