Growth pattern of isolated zoospores in Hydrodictyon reticulatum (Chlorococcales, Chlorophyceae)

Zoospores at various developmental stages in Hydrodictyon reticulatum were isolated from parent cells and cultured in Waris medium. Isolated zoospores grew to mature vegetative cells, and were able to reproduce zoo-spores that formed daughter hexagonal nets. Three types of shape appeared in cells 24 h after isolation: cylindrical, Y-shaped and 4-armed type. Protrusions of Y-shaped or 4-armed cells were formed at an angle of about 120° to the long axis of the cell. When cells were isolated at later stages, more cells became cylindrical in shape and fewer ceils became Y-shaped or 4-armed, Direction of cell growth also seemed to depend largely on the developmental stages of the zoospores. The later the isolated stages were, the more the cells elongated along the long axis of the zoospores.     

ULTRASTRUCTURE OF SWARMERS IN THE LAMINARIALES (PHAEOPHYCEAE). I. ZOOSPORES1

Zoospores of 17 species in 14 genera of Laminariales, collected in the northeast Pacific Ocean, were studied by electron microscopy. These zoospores are unique in the brown algae in lacking both an eyespot in the single chloroplast and any associated swelling at the base of the shorter, posterior flagellum. Spores of all species examined possess a distal whiplash portion on the longer, mastigoneme-bearing anterior flagellum. This appendage may sometimes be as long as the mastigoneme-bearing portion of the flagellum, but it is only seldom preserved in the preparations for electron microscopy. A microtubular cytoskeleton is probably responsible for maintaining the shape of the spore. It consists of a short band of about 10 microtubules between the two basal bodies, scattered tubules converging at the anterior of the spore, a band of 7–9 tubules directed anteriorly from the anterior basal body, and a band directed posteriorly from the posterior basal body. These anterior and posterior bands may form one continuous band looping around the periphery of the spore. Variation with possible taxonomic significance was found in the ultrastructure of vesicles which apparently contain adhesive material, and which are extruded through the plasmalemma when the zoospores settle.     

Formation of multinucleate zoospores inPhytophthora infestans (Mont.) De Bary (Oomycetes,Pythiaceae)

Summary Zoospore formation in sporangia ofPhytophthora infestans, the causal agent of potatoes downy mildew disease, was influenced by reduction of oxygen tension, by application of a respiratory poison (KCN), and by an inhibitor of cytokinesis (cytochalasine B). As demonstrated by different methods of light microscopy, in all three cases the percentage of morphologically abnormal, multinucleate, multiflagellate cells increased. High concentrations of KCN caused a complete inhibition of zoospore formation. These effects are interpreted as disorders of the process of cytokinesis during zoosporogenesis.     

Conditioning of surfaces by macromolecules and its implication for the settlement of zoospores of the green alga Ulva linza

Conditioning, ie the adsorption of proteins and other macromolecules, is the first process that occurs in the natural environment once a surface is immersed in seawater, but no information is available either regarding the conditioning of surfaces by artificial seawater or whether conditioning affects data obtained from laboratory assays. A range of self-assembled monolayers (SAMs) with different chemical terminations was used to investigate the time-dependent formation of conditioning layers in commercial and self-prepared artificial seawaters. Subsequently, these results were compared with conditioning by solutions in which zoospores of the green alga Ulva linza had been swimming. Spectral ellipsometry and contact angle measurements as well as infrared reflection absorption spectroscopy (IRRAS) were used to reveal the thickness and chemical composition of the conditioning layers. The extent that surface preconditioning affected the settlement of zoospores of U. linza was also investigated. The results showed that in standard spore settlement bioassays (45–60 min), the influence of a molecular conditioning layer is likely to be small, although more substantial effects are possible at longer settlement times.     

Studies on physiology,zoospore morphology and entomopathogenic potential of the aquatic oomycete: Lagenidium giganteum

The oomycete Lagenidium giganteum, a facultative parasite of mosquito larvae requires exogenous sterols for the genesis of zoospores when grown saprobically. Growth media prepared from oil rich materials such as soy or sunflower seed were very effective inducers of virulent zoospores. The external morphology of zoospores of L. giganteum was studied with the aid of philips scanning electron microscope 515. Zoospores were ovoid, bluntly pointed with the groove parallel to the long axis and 0.7 × 1.4 μm. Insect cell walls are known to contain lipid and chitin. L. giganteum was tested for chitinase activity and found to possess 0.76 ± SD0.14 chitinase activity. Use of oil seed for growth of the organism confirms phospholipase activity. Phospholipase production was studied further by egg-yolk plate method. Presence of these two key enzymes that can initiate host cell damage suggests the entomopathogenic potential of L. giganteum. L. giganteum failed to grow at 37 °C limiting its effectiveness in warmer climates. Introduction of this organism to variety of habitats with various mosquito species will demonstrate the efficacy of the organism as a bioinsecticide. This revised version was published online in June 2006 with corrections to the Cover Date.     

Development of a Real-Time PCR assay for quantitative assessment of uncultured freshwater zoosporic fungi

Recently, molecular environmental surveys of the eukaryotic microbial community in lakes have revealed a high diversity of sequences belonging to uncultured zoosporic fungi. Although they are known as saprobes and algal parasites in freshwater systems, zoosporic fungi have been neglected in microbial food web studies. Recently, it has been suggested that zoosporic fungi, via the consumption of their zoospores by zooplankters, could transfer energy from large inedible algae and particulate organic material to higher trophic levels. However, because of their small size and their lack of distinctive morphological features, traditional microscopy does not allow the detection of fungal zoospores in the field. Hence, quantitative data on fungal zoospores in natural environments is missing. We have developed a quantitative PCR (qPCR) assay for the quantification of fungal zoospores in lakes. Specific primers were designed and qPCR conditions were optimized using a range of target and non-target plasmids obtained from previous freshwater environmental 18S rDNA surveys. When optimal DNA extraction protocol and qPCR conditions were applied, the qPCR assay developed in this study demonstrated high specificity and sensitivity, with as low as 100 18S rDNA copies per reaction detected. Although the present work focuses on the design and optimization of a new qPCR assay, its application to natural samples indicated that qPCR offers a promising tool for quantitative assessment of fungal zoospores in natural environments. We conclude that this will contribute to a better understanding of the ecological significance of zoosporic fungi in microbial food webs of pelagic ecosystems.     

Complete genome sequence of the motile actinomycete Actinoplanes missouriensis 431T (= NBRC 102363T)

Actinoplanes missouriensis Couch 1963 is a well-characterized member of the genus Actinoplanes, which is of morphological interest because its members typically produce sporangia containing motile spores. The sporangiospores are motile by means of flagella and exhibit chemotactic properties. It is of further interest that members of Actinoplanes are prolific sources of novel antibiotics, enzymes, and other bioactive compounds. Here, we describe the features of A. missouriensis 431^T, together with the complete genome sequence and annotation. The 8,773,466 bp genome contains 8,125 protein-coding and 79 RNA genes.     

FINE STRUCTURE OF BIFLAGELLATE ZOOSPORES OF ASTEROCOCCUS SUPERBUS (TETRASPORALES, CHLOROPHYCEAE), INCLUDING THE ABSOLUTE CONFIGURATION OF THE FLAGELLAR APPARATUS

The ultrastructure of zoospores of Asterococcus superbus (Cienk.) Scherffel was studied to provide ultrastructural data relevant to the systematic position of the genus. Our results demonstrated that the motile cells of A. superbus were similar to those of the tetrasporalean algae, such as Tetraspora sp. and Tetrasporidium javanicum Moebius . The flagellar apparatus of A. superbus had the same clock-wise orientation of basal bodies and the V-shaped alignment of basal bodies as Tetraspora cylindrica (Wahlb.) Ag. and T. lubrica (Roth) Ag., but differed by having rhizoplasts . The motile cells of A. superbus displayed chlamydomonadal ultrastructure, similar to Chlamydomonas reinhardtii Dangeard , including the absolute configuration of the flagellar apparatus. The pyrenoid matrix in A. superbus, however , showed a large lateral invagination occupied by chloroplast stroma, a characteristic that has never been observed in Chlorophyta.     

Transmission of plant viruses by fungi

The evidence for the mechanisms involved in virus transmission by fungi is reviewed in relation to the non-persistent and persistent categories usually recognised. Non-persistent transmission by Olpidium spp. has been little studied in the last 20 years, but appears to depend on adsorption of virus to the outside of the fungal zoospores. This seems to be under the genetic control of both the virus (via its coat protein) and the vector. Such viruses are not transmitted in the fungal resting spores. The route by which the virus is transferred from the vector to the host may involve uptake into the zoospore but this deserves further study. Persistent transmission by Olpidium, Polymyxa and Spongospora spp. is less well characterised. Some of the evidence used for its support is inconclusive. The viruses are probably always carried inside zoospores, and they also persist in the fungal resting spores. Transmission depends on the genome of the vector and the virus, but not exclusively on the virus coat protein.