Coiling phagocytosis of trypanosomatids and fungal cells.

Coiling phagocytosis has previously been studied only with the bacteria Legionella pneumophila and Borrelia burgdorferi, and the results were inconsistent. To learn more about this unconventional phagocytic mechanism, the uptake of various eukaryotic microorganisms by human monocytes, murine macrophages, and murine dendritic cells was investigated in vitro by video and electron microscopy. Unconventional phagocytosis of Leishmania spp. promastigotes, Trypanosoma cruzi trypomastigotes, Candida albicans hyphae, and zymosan particles from Saccharomyces cerevisiae differed in (i) morphology (rotating unilateral pseudopods with the trypanosomatids, overlapping bilateral pseudopods with the fungi), (ii) frequency (high with Leishmania; occasional with the fungi; rare with T. cruzi), (iii) duration (rapid with zymosan; moderate with the trypanosomatids; slow with C. albicans), (iv) localization along the promastigotes (flagellum of Leishmania major and L. aethiopica; flagellum or posterior pole of L. donovani), and (v) dependence on complement (strong with L. major and L. donovani; moderate with the fungi; none with L. aethiopica). All of these various types of unconventional phagocytosis gave rise to similar pseudopod stacks which eventually transformed to a regular phagosome. Further video microscopic studies with L. major provided evidence for a cytosolic localization, synchronized replication, and exocytic release of the parasites, extending traditional concepts about leishmanial infection of host cells. It is concluded that coiling phagocytosis comprises phenotypically similar consequences of various disturbances in conventional phagocytosis rather than representing a single separate mechanism.

The surface layer of Mycoplasma mobile 163K and its possible relevance to cell cohesion and group motility.

Mycoplasma mobile strain 163K tends to move in multicellular configurations, either as pairs or small groups of three or more cells, or as chain-like aggregations or microcolonies. Such wandering groups arise by transient association of independently moving cells. This behaviour of M. mobile was microscopically investigated and documented by sequences of microcinematographic pictures, as well as by photomicrographically recorded motility tracks. The presence of an extracellular slime layer was demonstrated in thin sections, by negative staining and by scanning electron microscopy. The possible association of this layer with the cohesive properties of the mycoplasma cells, enabling the formation of wandering groups, is discussed and a calculation of the magnitude of the cohesive force is provided.