Membrane synthesis in synchronous cultures of Bacillus subtilis 168

Synthesis of bacterial membranes has been investigated in Bacillus subtilis by examining incorporation of amino acids and glycerol into the protein and lipid of membranes of synchronous cultures. A simple reproducible fractionation scheme divides cellular proteins into three classes (i) truly cytoplasmic, (ii) loosely membrane bound, released by chelating agents, and (iii) tightly membrane bound. These comprise approximately 75, 10, and 15%, respectively, of cellular proteins in this organism. Incorporation of radioactivity into these fractions, using steady-state and pulse labeling has been followed during the cell cycle. Cytoplasmic proteins and the loosely membrane-bound proteins are labeled at an exponential rate throughout the cell cycle. The membrane fraction is labeled discontinuously in the cell cycle, with periods of rapid synthesis over the latter part of the cycle and a period with no net synthesis during the early part of the cycle. Pulse labeling indicates that synthesis of membrane occurs at a linear rate that doubles at a fixed time in each cycle, which coincides with the period of zero net synthesis. Rates of membrane synthesis measured by pulse labeling during the period of rapid membrane synthesis are significantly less than indicated by steady-state labeling. These discrepancies are consistent with the hypothesis that during the cell cycle certain proteins are added to the membrane from the cytoplasm and that during the period of zero net synthesis there is an efflux of proteins from the membrane. Evidence in favor of this has been presented. The activity of succinic dehydrogenase (a representative of class c) varies in a step-wise manner with periods of rapid increase, approximately coincident with bursts of membrane protein synthesis, alternating with periods without any increase in activity. The activities of malate dehydrogenase (class a) and reduced nicotinamide adenine dinucleotide dehydrogenase (class b) increased throughout the cell cycle. Phospholipid synthesis is continuous throughout the cell cycle.

Morphogenesis and ultrastructure of Geotrichum candidum septa

The ultrastructure and mode of formation of septa of Geotrichum candidum were investigated by light and electron microscopy. The invaginations of the lateral membrane and wall appear to initiate at multiple points around the circumference of the cell; the immature septum subsequently assumes a cart-wheel shape, with branched spokes radiating from the center of the septum. Each face of the septum is covered with a membrane possessing hitherto undescribed structural differentiation; the membrane substructures are comprised of two central subunits encircled by 12 identical subunits. The diameter of the entire 12 plus 2 structure is 24 to 25 nm, and the diameter of each individual subunit is approximately 4 nm. The maturation of the septum appears to occur by further deposition of material along the branched skeletal regions. Numerous small openings (micropores), formed as a result of incomplete deposition, ultimately give rise to plasmodesmata. During arthrospore formation, the plasmodesmal canals and associated micropores are occluded by electron-dense materials, rendering each segment of the hyphae completely independent of the rest of the hyphae.

First generation synchrony of isolated Hyphomicrobium swarmer populations

A method is described for obtaining synchronously growing swarmer cell populations of Hyphomicrobium sp. strain B-522. This was accomplished by isolating young swarmers from random cultures by centrifugation and filtration. Cell multiplication occurred during 38% of the growth cycle in populations synchronized in this manner. Observations were made of the changes in cellular morphology which occurred during the growth cycle. Of the 14.25 h required for the doubling in cell numbers, an average of 5 h passed before the swarmer cells began to develop their hyphae. This time varied over a range of 10 h. The time interval between the beginning of hyphal development and the beginning of bud formation was 3.5 to 4.5 h. The maturation of the first buds and their separation from the mother cells were completed in 5.5 h. The duration of these steps is compared to those measured previously in agar slide cultures.

Morphology of bacteriophage-like particles from Desulfovibrio vulgaris

Phagelike particles obtained from a mitomycin C-induced lysate of Desulfovibrio vulgaris are described. Whether they can be classified as temperate bacteriophages or as bacteriocins has not been determined.

Studies on the developmental cycle of Chlamydia trachomatis: isolation and characterization of the initial bodies

The initial bodies which develop in the inclusion bodies of trachoma agent (Chlamydia trachomatis) were separated from the infected cells nuclei and cytoplasmic components by zone centrifugation in sucrose gradients. The initial bodies are the site of the agent's ribonucleic acid synthesis and serve as precursors to the elementary bodies. The conversion of the initial bodies to elementary bodies is through a process which resembles binary fission. The effects of antibiotics on the development of the trachoma agent initial bodies revealed that rifampin prevented and hydroxyurea affected the formation of the initial bodies. Penicillin led to the formation of structures larger than the initial bodies.

Penetration of host cell membranes by adenovirus 2

Highly purified human adenovirus type 2 directly penetrated the plasma membranes of KB cells. The process of membrane penetration resulted in the appearance of large numbers of adenovirions free in the cytoplasm of the infected cells. The virions underwent a morphological change as they penetrated the cell surface. Penetration of the plasma membranes and the accompanying alteration in virion morphology was dependent on a function associated with the intact cells, because neither event occurred when purified virions were added to isolated cell membranes. Inactivation of the adenovirions with heat or antibodies before inoculation of the cells reduced the infectivity of the virus population and prevented the appearance of virions free in the cytoplasm. The inactivation of the virions did not significantly reduce the number of virus particles which were found in cell vacuoles and pinocytotic vesicles.