Order of expression of genes affecting septum location during sporulation of Bacillus subtilis

The mean volumes of stationary-phase cells of wild-type and asporogenous mutants of Bacillus subtilis have been measured. Mutants blocked at stage 0 of sporulation either produced cells that had the same volume as the developing sporangium or they divided to produce cells of one-half this volume. The order of expression of the genes affected by the mutations in these strains was determined by biochemical characterization and by construction of double sporulation mutants. Mutants that produced small cells were blocked at an earlier stage of sporulation than those that produced large cells. It is suggested that the following dependent sequence must occur before the formation of the prespore spetum: (i) the initiation of sporulation, (ii) a signal to block the final central division site, and (iii) a signal to activate a polar septum site.

Subapical wall synthesis and wall thickening induced by cycloheximide in hyphae of Aspergillus nidulans

Hyphae of Aspergillus nidulans continued to synthesize all the major polysaccharide components of the cell wall when cycloheximide was added to cultures. In the presence of cycloheximide, hyphae did not elongate, but electron microscopy showed that the walls became thicker around the cell. The conclusion that cycloheximide changed wall synthesis from extension at the apex to subapical thickening was supported by grain distributions on radioautograms of mutant hyphae labeled with galactose. These findings are discussed in relation to the control of hyphal wall synthesis and are compared with the effects of protein synthesis inhibitors on wall formation in gram-positive bacteria.

Mode of cell wall growth of Bacillus megaterium

The growth of the cell wall of Bacillus megaterium KM was examined by labeling the cell wall uniformly with (3)H-alpha, epsilon-diaminopimelic acid and examining by radioautography the distribution of labeled cell wall material in daughter cells. The results indicate that the label is distributed uniformly to all daughter cells and rule out a single growth point, either central or apical, for these cells. The results strongly suggest that cell wall growth occurs by uniform deposition of new wall over the whole cell surface.

Cell wall growth in Bacillus licheniformis followed by immunofluorescence with mucopeptide-specific antiserum

Insertion of new wall during the growth of Bacillus licheniformis occurred discretely and probably at the sites of incipient cross wall formation.

Reinitiation of cell wall growth after threonine starvation of Streptococcus faecalis

Cultures of Streptococcus faecalis ATCC 9790 were starved of threonine for 10 hr and then allowed to reinitiate growth in a fresh complete medium. On regrowth, culture turbidity began to increase within 10 min, but the ability of cells to autolyze did not begin to increase until after 30 min. Ultrastructural studies of regrowth of the initially thick-walled cells showed, at about 30 min, centripetal linear extension of new thin cross wall. This was followed, at about 40 min, by a notching, splitting, and peeling apart of the base of the cross wall. After this, extension of new thin peripheral wall from the nascent cross wall appeared to push old thick wall toward the poles. After the first cell division, asymmetric cells with one initial generation thick-walled pole and one second generation thin-walled pole were seen. After two divisions, thick-walled hemispheres were still seen, suggesting conservation of old wall during this time. A small fraction of the initial cell population exhibited aberrations and difficulties in reinitiating linear wall extension and were useful in the establishment of a model for the reinitiation of linear wall extension.

An in vitro system that simulates plant cell extension growth

A new technique is described for studying controlled in vitro extension of plant cell walls. This technique uses frozen-thawed Avena coleoptile segments in which turgor is replaced by a constant applied force. In this system rapid extension is induced by low pH (3.0-3.6) but not by auxins or CO(2). Extensions of over 30% have been achieved. Our results indicate that cell wall synthesis is not required for rapid cell extension, and suggest that wall extension may be controlled by acid-labile, alkali-stable cell wall bonds.

Bacterial growth and the cell envelope

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Model for cell wall growth of Streptococcus faecalis

In exponentially growing and dividing cells of Streptococcus faecalis, it is proposed that the leading edge of the annularly closing cross wall is the point of extension for both cross wall and peripheral wall. Peripheral wall extension is thought to be produced by the separation or splitting of the cross wall at its junction with peripheral wall. This results in the pushing of the equatorial wall bands, found on S. faecalis walls, to subsequatorial positions. These bands therefore mark the separation of old wall from new wall. Mesosomal formation was observed usually to precede cross wall initiation.

The Ultrastructure and Ontogeny of Pollen in Helleborus Foetidus L

The first recognizable elements of the pollen grain wall of Helleborus foetidus are initiated in the cellulosic primexine which is formed immediately outside the microspore cytoplasm while the pollen grains are still in the tetrad configuration and enveloped in a thick layer of callose. Elements of the primexine give rise to the precursors of the rod-like bacula of the mature exine. The bacula increase in electron density due to the rapid deposition of sporopollenin, and begin to expand laterally at the outer side to form the tectum. There follows a lateral expansion on the inner side to form the foot-layer. Further deposition of sporopollenin is continued and all elements of the pollen grain wall expand outwards and laterally as the pollen grain enlarges. The enveloping callose disappears and the pollen grains are free in the thecal cavity. A secondary exine is deposited below the primary exine, particularly around the furrows. Initially this process involves a number of thin electron-transparent lines or lamellae about 4 nm thick that appear to arise from the cytoplasm and provide a locus around which sporopollenin is deposited. As the deposition proceeds, the lamellae thicken and finally merge with each other to form the secondary exine. No sign of the lamellae can be seen in the mature pollen grain wall. Towards the end of secondary exine formation the deposition of sporopollenin does not appear to be centred on thin lamellae, but appears as small granules which gradually coalesce. The secondary exine remains discontinuous in the region of the furrow, but becomes consolidated in the inter-furrow regions.

As the pollen grain matures the sporopollenin, which is electron-dense when initially deposited, becomes progressively less so.

The final stage in development is the deposition of the cellulosic intine, which forms inside the secondary exine and is associated with increased dictyosome activity and randomly oriented microtubules.

Fungal morphogenesis: cell wall construction in Mucor rouxii

An autoradiographic study revealed two different patterns of cell wall constructioni associated with two types of morphogenesis in Mucor rouxii. In hyphae, the cell wall was preferentially synthesized in the apical region; these cylindrical walls seemed to be generated by a sharply descending gradient of wall synthesis radiating from the apex. In spherical cells (germinating spores, yeast cells), wall formation occurred largely, if not entirely, in uniformly dispersed fashion over the entire cell periphery.

Inhibitory effect of 2-deoxy-d-glucose on the formation of the cell wall in yeast protoplasts

2-Deoxy-d-glucose (2DG) acted as a competitive inhibitor of the synthesis of cell wall components in Saccharomyces cerevisiae protoplasts. The synthesis of fibrillar glucan cell wall component was inhibited at a glucose to 2DG ratio of 4:1 in the cultivating medium. The completion of the formation of cell wall by the synthesis of the amorphous mannan-protein cell wall component was inhibited at a glucose to 2DG ratio of about 20:1. The inhibition could be reversed by increasing the glucose to 2DG ratio in the nutrient medium. No incorporation of 2DG into fibrillar glucan cell wall component was observed.

Cell wall growth during differentiation of Proteus swarmers

This paper describes the process by which the cell wall of Proteus mirabilis, as measured by the presence of the O antigen, develops during the differentiation of swarmers from short cells on an agar surface. The sequence was followed by fluorescent-antibody staining, with both the direct and reverse methods. When the organisms were labeled with fluorescent antibody by the direct method, they showed a progressive diminution of the marker along the cell surface and some increase in the length of the bacteria. However, the label had become completely diluted out before typical swarmers developed. When the bacteria were exposed initially to unlabeled antibody by the reverse technique, and then incubated with fluorescent antibody, they showed a progressive increase both in the intensity of the label along their entire periphery and in cellular length, culminating in the formation of swarmers. It is concluded that in P. mirabilis, as in the few other gram-negative bacteria examined so far, cell wall synthesis takes place diffusely, i.e., by intercalation of new with old components along the length of the cell wall.

Nutritional requirements for cell wall synthesis in Micrococcus lysodeikticus

Preferential cell wall synthesis in Micrococcus lysodeikticus, as determined by an increase in the dry weight of the cell wall, took place in a medium containing DL-glutamic acid, DL-alanine, L-lysine, glycine, magnesium ions, glucose and phosphate buffer, pH 7.0. Cell wall synthesis could not be completely dissociated from protein synthesis in the 'cell wall' medium. The cell wall synthesized in the defined medium accounted for 40–56% of the total dry weight increase of the cells. Chloramphenicol had no effect on cell wall synthesis. Incorporation of uracil and guanine in the medium did not result in any increase in the amount of cell wall synthesized. DL-Glutamic acid alone, or a mixture of the three amino acids DL-alanine, L-lysine, and glycine, were capable of replacing the four amino acids present in the complete medium, but under these conditions the total dry weight of cell wall synthesized was only 75% of that produced in the complete medium. There was no reduction in cell wall synthesis when L-glutamic acid replaced DL-glutamic acid, L-alanine replaced DL-alanine, or sucrose replaced glucose in the cell wall medium. Deprivation of magnesium ions produced the greatest decrease in wall synthesis; this was the most important single factor involved in cell wall synthesis which was studied in the present investigation. There was no observable change in the chemical composition of the cell wall synthesized in the 'wall' medium when compared to that synthesized by cells grown in a complex medium.