Stefania Pellegrini

LYSIS OF MICROCYSTIS AERUGINOSA (KÜTZ.) BY BDELLOVIBRIO‐LIKE BACTERIA1

Cells of Microcystis aeruginosa (Kützing), collected from water‐blooms of Lake Varese, were lysed by Bdellovibrio‐like bacteria. The cells were lysed only after penetration. The cyanobacteria and lysing bacteria were characterized by a fibrous glycocalyx. Once the host cell was penetrated, the bacteria remained localized mainly between the host cell wall and cytoplasmic membrane, which appeared partially thickened. Cell lysis began by breakdown of cell structures. The cell wall appeared broken at many sites, and in completely lysed cells, was partially interrupted. The lysis of Microcystis by bacteria could be one of the causes of the death of algal blooms.

Ultrastructural alterations induced by rice tungro virus in rice leaves.

Abstract Particles of rice tungro virus (RTV) were found in phloem parenchyma and companion cells. The most relevant alterations found in these cells were viroplasms and tubular inclusions. Virus particles, viroplasms and tubular inclusions were never observed in mesophyll parenchyma cells. However, the latter contained altered chloroplasts with taillike protrusions and an accumulation of heavy amounts of starch.

Differences in Septal Pore Apparatus Ultrastructure of Tremella Mesenterica

SUMMARYMany discussions about taxonomic significance of dolipore/parenthe-some ultrastructure have been published, during the last few years. However, the problem is difficult because, in the majority of Basidiomycetes, the real function of the pore cap is undecided. Our research shows that the dolipore/parenthesome ultrastructure of Tremella mesenterica Fries, varies according to its location, either in the secondary micelium hyphae, or at the basidum base, or in the conidiophore hyphae. In addition, the conidiophore hyphae extremities, when dividing to form conidia, form a passage that is always without a parenthesome. This variability suggests that dolipore-/parenthesome morphology is connected with different functions, according to its location.

Microbes in deep-sea anoxic basins

Abstract Biological studies on the anoxic basins of the Eastern Mediterranean started after the discovery of gelatinous matter of organic origin. The laminar gelatinous matter was observed within the cores containing anoxic sediments obtained during oceanographic expeditions for geological study of the Mediterranean Ridge. Microbiological and ultrastructural investigations were carried out on core sediment samples and on the overlying water. The organic nature of the mucilaginous pellicles found in the cores and their relation with numerous microbic forms present in all the samples were demonstrated. Viable microorganisms, prevalently Gram negative and aerobic as well as facultative anaerobes, were found in the water samples. Different microbic forms were isolated in pure culture : a vibrio ( Nitrosovibrio spp.), a coccus ( Staphylococcus spp.) and some rods of the family Pseudomonadaceae . In addition, laminar formations were observed in growth medium of mixed cultures that could be interpreted as the first stages of the mucilaginous pellicles seen in the cores.

Fine Structures of the Fungal Septa on Varieties of Basidiomycetes

SUMMARYIn this work the authors limite their researches to species belonging to several genera of superclass Homobasidiomycia (MOORE 1978) and to some species belonging to Dacrymycetales that is considered a thorough order towards the class Holobasidiomycetes. All the species considered here possess dolipores with well defined pore caps which may be perforate or imperforate but the differences in dolipore ultrastructures cannot contribute to clarify the taxonomy of Basidiomycetes but not in conjunction with other characters and functions, as basidiocarp morphology and so on.

The Effects of Various Light Intensities on Nostoc Punctiforme (Kützing)

SUMMARYWe studied by light and electron microscopy the influence of different intensities and periods of illumination on the life cycle and morphogenesis of Nostoc punctiforme (Kutz.) grown in nitrogen-free medium. By using light intensities between 500 and 2800 lux it was observed that the developmental cycle of N. punctiforme consists of a complete heterocystous phase and o a truncated sporogenous phase. The first phase is characterized by aseriate, spherical, or elongated colonies formed by a filament of vegetative cells and heterocysts. The filament is always enveloped in a watery or firm sheath which forms a surface pellicle. The sporogenous phase stops with the formation of coccoid cells formed along the filament of aseriate colonies. The coccoid cell may be released or remain in the mother colonies where they germinate originating directly new aseriate colonies. The nature and functions of such particular cells, which are considered immature spores are discussed.The various light intensities influe...

Septal Pore Apparatus Ultrastructure in Tremella Foliacea Pers. Ex Fr. and Tremellodon Gelatinosum (Scop.) Pers.

SUMMARYMost Basidiomycetes are characterized by dolipores with parenthesomes that are multiperforate, imperforate or pauciperforate. Electron micrographs of Tremellae, however, show dolipore septa with banded material in the orifices and vesiculate parenthesomes. We have studied the fine structure of Tremella foliacea Pers. ex Fr. and Tremellodon gelatinosum (Scop.) Pers. In these two species we describe several considerable differences which question the phylogeny suggested by some authors, within the Basidiomycetes. Ultrastructural similarities found in the dolipore of Tremella foliacea and in the pore of a few Ascomycetes could suggest that the most primitive dolipore is the Tremella-type.

Effects of Various Nitrogen Sources on Nostoc Punctiforme (Kützing)

SUMMARYThe modifications which accompany the growth of Nostoc punctiforme in culture media containing various forms of mineral nitrogen were described by light and electron microscopy. The presence of 0.012M NaN03 and 0.04M NH4Cl inhibit heterocyst formation, while lower doses reduce their frequency. Parallel to the disappearance of heterocysts is the disappearance of the aseriate stage, so that the whole culture is made by long filaments formed by vegetative cells and, in particular conditions, by cells similar necridia and discs. When grown in presence of nitrogen compounds, the vegetative cells contain numerous and large cyanophycin granules. The higher large amounts of nitrates induce the formation of particular vegetative cells deprived of cyanophycin and enveloped in abundant mucilage. Some of these particular cells are similar to analogous found in the gonidial zone of coralloid roots of Cycads. The absence of true spores in the different culture media is discussed.

Ultrastructural variations in Microcystis aeruginosa (Chroococcales, Cyanophyta) during a surface bloom induced by high incident light irradiance

ABSTRACT We evaluated the ultrastructural variations occurring during a surface bloom in Microcystis aeruginosa Kützing PCC 7005, by comparing cultures exposed to high incident light irradiance (90 µmol photons m-2 s-1) and to low irradiance (9 µmol photons m-2 s-1). At 12h, and 15 and 30 days in culture, the cells were fixed in glutaraldehyde and subjected to cytochemical assays. Exposure to high irradiance induced structural changes in the cell wall, and differences in the photosynthetic apparatus and granule reserves. After 15 days of high irradiance, the following features were observed: a reduced number of thylakoids and changes in their arrangement; high accumulation of glycogen, poly-beta-hydroxybutyrate, lipid bodies and cyanophycin; conspicuous structural changes in the cell wall. At day 30 of high irradiance, the viable cells had few thylakoids, arranged parallel to each other and perpendicular to the plasma membrane, and abundant glycogen. Nitrogen, calcium and phosphorus, as detected by electron spectroscopic imaging, were present in different sites of cells grown at low and high irradiance. The results of this study, together with previous data on variation in Fe-superoxide dismutase (Canini et al., 2001a), suggest that defense mechanisms against high and prolonged irradiance only operate for a short time.

Structures of Sclerotinia Sclerotiorum Ascocarp and its Septal Pore Ultrastructure

SUMMARYIn this study, it is taken into consideration the cellular modifications during the development of fertile hyphae from the apothecium of Sclerotinia sclerotiorum and the ultrastructure of the transverse septum at different levels of ascocarp hyphae. Moreover enzymatic digestions have been performed to ascertain the chemical nature of the various inclusions and of the organelles associated to the septal pore.