No abstract

The most complete account to date of the ultrastructure of flagellate cells in diatoms is given for the sperm of Thalassiosira lacustris and Melosira moniliformis var. octogona, based on serial sections. The sperm are uniflagellate, with no trace of a second basal body, and possess a 9 + 0 axoneme. The significance of the 9 + 0 configuration is discussed: lack of the central pair microtubules and radial spokes does not compromise the mastigoneme-bearing flagellum's capacity to perform planar beats and thrust reversal and may perhaps be related to sensory/secretory function of the sperm flagellum during plasmogamy. The basal bodies of diatoms are confirmed to contain doublets rather than triplets, which may correlate with the absence of some centriolar proteins found in most cells producing active flagella. Whereas Melosira possesses a normal cartwheel structure in the long basal body, no such structure is present in Thalassiosira, which instead possesses 'intercalary fibres' linking the basal body doublets. No transitional helices or transitional plates are present in either species studied. Cones of microtubules are associated with the basal body and partially enclose the nucleus in M. moniliformis and T. lacustris. They do not appear to be true microtubular roots and may arise through transformation of the meiosis II spindle. A close association between cone microtubules and tubules containing mastigonemes may indicate a function in intracellular mastigoneme transport. No correlation can yet be detected between methods of spermatogenesis and phylogeny in diatoms, contrary to previous suggestions.

cGametogenesis and auxospore development have been studied in detail in surprisingly few centric diatoms. We studied the development of sperm, eggs and auxospores in Actinocyclus sp., a radially symmetrical freshwater diatom collected from Japan, using LM and electron microscopy of living cultures and thin sections. Actinocyclus represents a deep branch of the ‘radial centric’ diatoms and should therefore contribute useful insights into the evolution of sexual reproduction in diatoms. Spermatogenesis was examined by LM and SEM and involved the formation of two spermatogonia (sperm mother-cells) in each spermatogonangium through an equal mitotic division. The spermatogonia produced a reduced ‘lid’ valve, resembling a large flat scale with irregular radial thickenings. Sperm formation was merogenous, producing four sperm per spermatogonium, which were released by dehiscence of the ‘lid’ valve. The sperm were spindle-shaped with numerous surface globules and, as usual for diatoms, the single anterior flagellum bore mastigonemes. One egg cell was produced per oogonium. Immature eggs produced a thin layer of circular silica scales before fertilization, while the eggs were still contained within the oogonium. Sperm were attracted in large numbers to each egg and were apparently able to contact the egg surface via a gap formed between the long hypotheca and shorter epitheca of the oogonium and a small underlying hole in the scale-case. Auxospores expanded isodiametrically and many new scales were added to its envelope during expansion. Finally, new slightly-domed initial valves were produced at right angles to the oogonium axis, after a strong contraction of the cell away from the auxospore wall. At different stages, Golgi bodies were associated with chloroplasts or mitochondria, contrasting with the constancy of Golgi–ER–mitochondrion (G-ER-M) units in some other centric diatoms, which has been suggested to have phylogenetic significance. Electron-dense bodies in the vacuole of Actinocyclus are probably acidocalcisomes containing polyphosphate.

Background and aims – Diatoms are one of the most species rich groups of organisms on Earth. They are fundamental in supporting the biomass of the natural environment. The presence of marine viruses can greatly influence diatom diversity in their natural environment and has attracted interest from multi-disciplinary research teams after a diatom infected virus was reported for the first time in the 21st century. As initial research in this field demonstrated, for the acquisition of a new virus it is important to learn about their infect hosts. Therefore, we have been searching for new viruses that infect diatoms. Methods – A clonal host species Nitzschia reversa was isolated from natural sea water. Aliquots of the filtrates obtained from this sea water were inoculated to yield the exponentially-growing isolated host species. The resultant lysate was used as a clonal lysate and treated as a clonal virus suspension. The suspension was then used for further analysis of various biochemical studies. Key results – We discovered and isolated a new virus that infected the pennate diatom Nitzschia reversa. Since this newly discovered virus was a single strand RNA virus, it has capsid proteins with 30 nm size icosahedron without an envelope. The species epithet is NitRevRNAV. Conclusions – In this study, we described the morphology, genome type and partial sequences, as well as lytic activities, of the new species NitRevRNAV. Of note, the virus harbours a positive-sense single-stranded RNA genome. These features were highly similar to those of previously known diatom RNA viruses therefore NitRevRNAV is a new member of the genus Bacillarnavirus in the Order Picornavirales.

We can detect cancer in the early stages by validating the expression of cancer specific nucleic acids in the blood. In this report, we have developed the micro device for performing real-time polymerase chain reaction (real-time PCR), one of the methods used for determining the quantity of nucleic acids, using a small volume of reagent. This all-in-one device can perform real-time PCR with the inclusion of heating control and the analyzing system with optical sensor.