SUMMARYThe sequence of flagellar development accompanying differentiation during multiplication in a plate culture of Proteus mirabilis was investigated with the electron microscope and the negative-staining technique; the sequence of development can best be seen from the electron micrographs. The first flagella were produced towards the end of the first hour, and increased to a peak at about 6 hr and then decreased. The bacteria changed from coccoid to rod-shaped to elongated forms; the latter measured up to 80 , u in length and were equipped with several thousand flagella. On the basis of measurements of flagellar complement, the elongated forms (or swarmers) can be regarded as ' flagellin-factories '. The fine structure of both flagella and fimbriae was examined and several new features were seen, in particular certain structures at the bases of both appendages, The diameter of Proteus fimbriae was found to be about 40 A.

This paper reinvestigates the gross changes which follow the inoculation of Proteus mirabilis onto an agar plate. The sequence of development observed by earlier workers was confirmed: namely, the development of a primary colony at the site of inoculation, followed by alternating periods of swarming and consolidation. The paper"s main contribution is the demonstration, by means of time-lapse photography through the phase-contrast microscope, of the cellular changes which occur during the various stages—in particular, the differentiation of short rods into swarmers, the swarming process itself, the subsequent breakdown of the swarmers into progressively shorter units, and the multiplication of these rods. Of special note is the clear demonstration that most of the swarmers are normal viable cells.

This paper describes the changes in nuclear complement, cytoplasm, and cell wall which take place when short rods of Proteus mirabilis differentiate into long swarmers. In the swarmers themselves, definite cellular units are mapped out at intervals of 1.2 to 1.8 μ. These units consist of a nucleus (or paired nuclei) and the adjacent cytoplasm, there being apparently no cross septa between successive units. The cytology of the swarmers has been compared with that of long forms of P. mirabilis induced by penicillin, lithium chloride, ultraviolet light, and gamma radiation. Depending on the inducing agent and dosage, such long forms frequently have abnormal-looking nuclei and malformed cell walls, and thus contrast strikingly with the spontaneously arising swarmers.

STOKES. 1973. The fine structure of Sphaerotilus nafatrs.Can. J. Microbiol. 19: 309-313. Sphaerotilus natans developed sheathed filaments in stationary liquid cultures and motile swarm cells in shaken ones. Electron microscopy of negatively stained preparations and thin sections showed that the sheath consists of fibrils. When the filaments wcre grown in broth with glucose added, the sheath was much thicker and the cells were packed with granules of poly-!3-hydroxybutyrate.Swarm cells possess a subpolar tuft of 10 to 30 flagella and a polar organelle which is usually inserted in a lateral position and believed to be ribbon-shaped. The polar organelle consists of an inner layer joined by spokes to an accentuated plasma membrane. The flagellar hook terminates in a basal disk, consisting of two rings, which is connected by a central rod to a second basal disk. HOENIGER, J. F. M., H.-D. TAUSCHEL et J. L. STOKES. 1973. The fine structure of Splrnerotilus natans.Can. J. Microbiol. 19: 309-313. Sphaerotilus nafans developpe des filaments feuilletes dans des cultures liquides stationnaires, et des cellules "swarm" mobiles dans des cultures agitks. La microscopic Blectronique de preparations colorees negativement et de sections minces montre que ces feuillets consistent en des fibrils. Lorsque les filaments se developpent en bouillon additionne de glucose, le feuillet est beaucoup plus Bpais et les cellules sont remplies de granules de poly-!3-hydroxybutyrate.Les cellules "swarm" possedent une touffe sous-polaire de 10 A 30 flagelles et une organelle polaire qui est habituellement pla& en position laterale et est probablement en forme de ruban. L'organelle polaire consiste en une couche interne jointe par des pics A une membrane plasmique accentuee. Le crochet flagellaire se termine par un disque basal, consistant en deux anneaux, lesquels sont connectes par une tige centrale i un deuxieme disque basal.[Traduit par le journal]

The process by which dormant spores of Clostridium sporogenes are transformed into vegetative cells has been studied in thin sections with the electron microscope. The resting spore appears very similar to that of other Bacillaceae for it possesses a rather featureless core which is surrounded by a core membrane, cortex, and spore coat(s); beyond lies a sac-like exosporium. At an early stage in germination the core becomes differentiated into peripheral areas of nuclear material and a ribosome-packed cytoplasm; a germ cell wall develops beyond the core membrane. The later stages of germination coincide with the beginning of outgrowth: the cortex disintegrates into a sponge-like mass of fibrils, and the young cell grows while still retained within the unbroken spore coats. The young cell now has a fibrillar nucleoplasm, a ribosome-rich cytoplasm, an occasional mesosome, a plasma membrane, and a relatively thick cell wall. Subsequently, the cortex vanishes completely, and the new vegetative cell elongates and finally emerges terminally through the spore coats and the exosporium. The exosporium of C. sporogenes consists of two layers: a thick inner one which is laminated, and a thin outer one possessing a fringe of hair-like projections.