No abstract

Germfree mice housed in isolators under controlled environmental and nutritional conditions were associated with an intestinal microflora. These associated animals and germfree mice drawn from the same population were tested for the rate at which the epithelial cells transited from the crypts of Lieberkuhn to the tips of the villi in their small intestines. The method for estimating the rate of transit of epithelial cells involved the use of liquid scintillation counting to determine the amount of radioactivity entering the cells while the animals were being injected with [3H]thymidine and statistical analysis of the data with a computer program developed for the purpose. As estimated by that method, the cells transited from the crypts to the villous tips in germfree mice in about 115 h and in the associated animals in about 53 h. In monoassociated mice, a strain of a Lactobacillus sp. had no effect on the transit time of the epithelial cells. A strain of Torulopsispintolopesii stimulated uptake of [3H]thymidine by the small bowel mucosae in mice monoassociated with the organisms for 5 weeks. In animals monoassociated with the yeast for 3, 4, and 6 weeks, however, the radioactive compound was incorporated into the bowel mucosae to the same extent as the mucosae of germfree mice. Therefore, similarly to the Lactobacillus strain, T. pintolopesii has no obvious influence on the transit rate of small bowel epithelial cells.

A freeze-fracture study has provided new information about the filamentous, segmented microorganism known to live in the murine small bowel. The intracellular bodies produced by this microbe appear to arise by a modified sporogenesis so that they are enclosed in an envelopment membrane at least prior to release by the filament mother cell. At least some of the intracellular bodies divide while still within the mother cell, suggesting a reproductive role for these structures. The host epithelial membrane remains intact at the site of attachment, but does appear to have a reduced concentration of intramembrane particles. Changes in the host cytoplasm adjacent to the attachment site are documented and interpreted to be a sol-gel transformation which may stabilize the attachment socket.

In both freeze-etched and critical-point dried preparations examined by transmission and scanning electron microscopy, respectively, the outer surfaces of the cells of Spirillum serpens VHL assume a wrinkled appearance 10-15 min after challenge by Bdellovibrion bacteriovorus 109D. This wrinkling effect is believed (on circumstantial evidence) to be caused by the bdellovibrio's disruption of the cell wall lipoprotein of the Spirillum. With the exception of those topological changes caused by wrinkling, the outer membrane of the Spirillum cell wall retains a normal appearance, as viewed in freeze-etched preparations, even after the Spirillum cell has been converted into a bdelloplast. Although the peptidoglycan layer of the Spirillum cell presumably is weakened somewhat by the invading Bdellovibrio, evidence obtained from freeze-fractured preparations of Spirillum bdelloplasts suggests that the peptidoglycan remains as a discrete cell wall layer, even though the Spirillum cell wall apparently has lost much of its rigidity. That the peptidoglycan backbone remains essentially intact, even after the Spirillum cell has been entered by the Bdellovibrio, is supported by the observation that the soluble amino sugar content of the culture medium, as determined by chemical analysis, does not rise even 5.0 h after the association of the Bdellovibrio with the Spirillum has begun.

Phenotypic expressions of morphogenesis and fine structure of Leucothrix mucor were determined when the organism was grown with and without added CaCl2 in a synthetic seawater medium. Evidence is presented to show that a bulb can form in the absence of a knot formation and that a bulb may give rise to a "germ-tube." In comparison with normal cells, which show transverse septa at right angles to the axis in dividing cells, the bulbs exhibited transverse septa at odd angles, which may explain the mechanism of bulb formation. The most striking morphological feature due to Ca++ deficiency was the absence of rosettes; instead, the culture showed an extremely filamentous morphology and a peculiar cord formation. Also, the Ca++deficient cells contained heavily stained intracytoplasmic granules which possibly represent tight packing of the smaller particles of ribonucleoprotein. Various bulbous forms observed in the Ca++-deficient culture showed more pronounced elaboration of mesosomes as intracytoplasmic structures than those seen in the complete medium.