Morphotype V of theBlastocaulis-Planctomyces group of budding and appendaged bacteria:Planctomyces guttaeformis Hortobágyi (sensu Hajdu)

The ultrastructure of a budding and appendaged bacterium resemblingPlanctomyces guttaeformis Hortobágyi (sensu Hajdu) was examined by transmission electron microscopy in negative-contrast and thin-section preparations from samples of pond and lake water in which natural blooms of this organism had occurred. Its prokaryotic nature was established, and observations were reported regarding its characteristic bulbiform or bulbose cell shape (cylindrical with one globose or swollen end), budding process, crateriform surface structures, rosettes (cell clusters) radiating from the narrow (nonglobose) ends of the adhering cells, cell envelope profile, and distinctive appendages (a single, relatively broad and long, gradually tapered, rigid, multifibrillar, polar or slightly subpolar, noncellular spike—without the adherence function of a stalk—located at the swollen pole of the bulbiform cell; numerous pili/fimbriae all over the globose portion). These traits establish the organism as a putative member of theBlastocaulis-Planctomyces group of budding and appendaged bacteria, but sufficiently distinctive (bulbiform cell shape; spike; adherent material at narrow end of cell rather than at the end of a noncellular appendage) to warrant its delineation as morphotype V of this group.