Biomedical subjects
Publications and source records attributed to M DWORKIN.
A method has been found for inducing the rapid, quantitative, and relatively synchronous conversion of vegetative rods of a fruiting myxobacterium to microcysts. The conversion is induced by the addition of 0.5M glycerol to a dispersed, growing, liquid culture of Myxococcus xanthus. The vegetative rods are converted to microcysts in about 120 minutes.
Dworkin, Martin (University of Minnesota, Minneapolis), and Donald J. Niederpruem. Electron transport system in vegetative cells and microcysts of Myxococcus xanthus. J. Bacteriol. 87:316-322. 1964.-Respiration by intact cells of the fruiting myxobacterium Myxococcus xanthus is cyanide-sensitive and can be demonstrated in the vegetative cells but not in the microcysts. Cell-free particles from both vegetative cells and microcysts have cyanide-sensitive reduced nicotinamide adenine dinucleotide (NADH) oxidase, diaphorase, NADH cytochrome c reductase, and cytochrome oxidase activities. While the vegetative cell specific activities for NADH oxidase and diaphorase are slightly higher than those for the microcysts, the microcysts have ten times the cytochrome c reductase and cytochrome oxidase activities of the vegetative cells. Furthermore, the respiration of the microcyst particles is considerably less cyanide-sensitive than is that of the vegetative-cell particles. Difference spectra of the cell-free particles of vegetative cells and microcysts are qualitatively identical, showing the presence of b- and c-type cytochrome and flavoprotein. The a-type pigments are clearly present in the extracts of the vegetative cells and are suggested by the spectrum of the microcyst particles. The cytochrome oxidase activity of both extracts is consistent with the presence of a-type pigments in both. The spectra of the carbon monoxide-binding pigments were determined and, by this parameter, qualitative differences appear between the vegetative cells and the microcysts.
Dworkin, Martin (University of Minnesota, Minneapolis). Nutritional regulation of morphogenesis in Myxococcus xanthus. J. Bacteriol. 86:67-72. 1963.-Fruiting-body formation by Myxococcus xanthus can be induced by omitting phenylalanine and tryptophan from the chemically defined growth medium. This effect was specific for these two amino acids and was not attributable to a nonspecific lowering of the growth rate. A complex pool of amino acids is present in vegetative cells of M. xanthus. Nutritional environments leading to morphogenesis also result in a decrease in the level of this pool. These changes have been described.
Explore the source record for details and available documents.
Dworkin, Martin (Indiana University Medical Center, Indianapolis, Ind.). Nutritional requirements for vegetative growth of Myxococcus xanthus. J. Bacteriol. 84:250-257. 1962.-This investigation was part of a program to clarify the environmental regulation of fruiting-body formation in a fruiting myxobacterium. By use of a dispersed-growing strain of Myxococcus xanthus, the nutritional requirements for vegetative growth have been defined. Exponential growth will take place on a medium containing 17 amino acids and salts. The generation time is 8 to 10 hr. Various optima have been established. There are no requirements for exogenous vitamins, and, with the exception of glycogen, a variety of organic materials do not significantly stimulate growth.
Voelz, Herbert (Indiana University Medical Center, Indianapolis) and Martin Dworkin. Fine structure of Myxococcus xanthus during morphogenesis. J. Bacteriol. 84:943-952. 1962.-This investigation concerns the nature of the structural changes in Myxococcus xanthus during cellular morphogenesis. These changes have been investigated by means of electromicrographs of thin sections of cells taken during various stages of the life cycle. The conversion of vegetative cells to microcysts involves the formation of a capsule but no drastic reorganization of the limiting cell membranes. Vacuoles appear in the cell during microcyst formation and germination. Microcyst germination involves a separation of the inner cell and the outer sheath, followed by the dissolution of a segment of the outer sheath and the emergence of the cell. Dense bodies within the cytoplasm and peripheral bodies between the two limiting membranes have been observed.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Endogenous photosensitization in a carotenoidless mutant of Rhodopseudomonas spheroides has been studied. When this mutant is exposed to visible light and oxygen there is a short lag period followed by exponential killing of the cells. The killing process obeys the Bunsen-Roscoe law of reciprocity and is temperature-independent. The chlorophyll content of the cells does not affect the rate of killing until a certain low threshold has been reached. Exposure of photosynthetically grown cells to air in the dark induces a temporary desensitization to the killing. A certain proportion of the population is invariably resistant to the photokilling. Evidence is presented to show that the resistance of these cells is probably a result of their abnormally low chlorophyll content. One consequence of the irradiation is the appearance of abnormally small colonies upon plating the survivors. This is interpreted in terms of a multi-hit theory. The photosensitizing pigment itself (the intracellular bacteriochlorophyll) is destroyed. The process is zero order, temperature-dependent, and does not follow the reciprocity law. It is suggested that the death of the cell results from a disruption of the cell membrane.
Explore the source record for details and available documents.
Explore the source record for details and available documents.