Shigeki Mayama

Heterothallic auxosporulation, incunabula and perizonium in Pinnularia (Bacillariophyceae)

The cytology and life cycle of Pinnularia cf. gibba was examined in nine clones from three Scottish localities. This freshwater epipelic diatom is heterothallic and produces two isogametes per gametangium in type IC auxosporulation (Geitlers classification [1973]). The zygote undergoes a highly unusual metamorphosis before beginning expansion, becoming shortly linear–lanceolate; this is accompanied by formation of a complete covering of thin, oxidation-resistant strips and scale-like structures (at the poles), which are quite separate from the perizonium formed during auxospore expansion. Observations of similar incunabular structures in P. acidojaponica show that these elements are siliceous. The P. cf. gibba perizonium also has unusual features, including a remarkably wide primary band. Trikaryotic and haploid auxospores are sometimes formed and haploid ‘zygotes’ mature and expand like diploids, but do not develop into mature initial cells. Several phases of mucilage secretion take place, from the gametangia, zygotes and auxospores. Triplets of gametangia and polyspermy occurred with high frequency; this and the systematic significance of variation in auxospore, incunabula and perizonium structure, are discussed. Aspects of the taxonomy of the P. gibba group are treated in supplementary material provided on the European Journal of Phycology website.

Morphological and molecular phylogenetic analysis of the high triglyceride‐producing marine diatom, Fistulifera solaris sp. nov. (Bacillariophyceae)

Fistulifera sp. strain JPCC DA0580, a marine pennate diatom, contains extremely high levels of intracellular triglyceride and has been suggested as a promising source of feedstock for biodiesel fuels. JPCC DA0580 was isolated from a mangrove swamp located in Sumiyo Bay below the mouths of the Sumiyo and Yakugachi Rivers in Amami‐Ohshima, Kagoshima, Japan. In this study, the morphology and the 18S rDNA sequence of JPCC DA0580 were compared with those of other Fistulifera strains. JPCC DA0580 possesses morphological characters of the genus Fistulifera, namely lightly silicified frustules, a distinct median costa (raphe sternum), and a wart‐like central pore (fistula). Morphometric analysis revealed that JPCC DA0580 differs from other Fistulifera species by the presence of a valve with coarser striation and coarser areolation. On the basis of 18S rDNA phylogeny, JPCC DA0580 formed a well‐supported clade with other members of the Fistulifera species complex, although the number of nucleotide substitutions was highest in JPCC DA0580. Our results led us to propose the taxonomic name Fistulifera solaris sp. nov. for JPCC DA0580.

Diversity of mineral cell coverings and their formation processes: a review focused on the siliceous cell coverings

Abstract.Mineral cell coverings are found in various protists. Some macroalgae accumulate calcium carbonate in the intercellular space, and some unicellular organisms use calcium carbonate or silica for the construction of loricas, scales, and frustules. Diatoms are representatives of those utilizing silica for the material of the cell covering called a frustule. The development of the frustule is initiated in a silica-deposition vesicle (SDV), which occurs just beneath the plasma membrane and, subsequently, the silicified cell covering expands its area, following the expansion of the SDV from valve face to valve mantle. Sequential valve development with whole valves is reviewed in several diatoms placed in different phylogenetic positions. Every diatom commences its valve formation from its pattern center and then develops by means of individual procedures. The results indicate that the valve development reflects the phylogeny of diatoms. In addition, recent progress in silica biomineralization is briefly reviewed, and the phylogeny of ability concerning siliceous cell covering formation is inferred.

Biomass, species composition and diversity of epipelic algae in mire pools

The biomass, species composition and diversity of epipelic algae in two small pools of contrasting physicochemical characteristics in Miyatoko Mire were studied in 1992 (pool 3 =site B4 and pool 50 =site D2). A total of 93 species and 67 species of epipelic algae occurred at sites B4 and D2, respectively. Considerable differences were observed between the two sites in the seasonal fluctuations of species number, biomass and dominant species. At site B4, little changed with species number during April–August and markedly increased in October, while biomass was largest in April and gradually decreased during June–October. Diatoms and desmids occupied 33–82% and 15–63% of total algal biomass, respectively. At site D2, species number and biomass were small in April just after the snow-thaw, and increased in June and decreased in August and October. Diatoms occupied 90–98% of total algal biomass. The species diversity was always higher at site D2 than B4. As a result of analyses of water chemistry in the two pools, pool B4 can be recognized as a habitat experiencing high disturbance frequency. It is predicted that pools experiencing frequent disturbance will have less epipelic algal biomass and diversity.

Regulated growth of diatom cells on self-assembled monolayers

We succeeded in regulating the growth of diatom cells on chemically modified glass surfaces. Glass surfaces were functionalized with -CF3, -CH3, -COOH, and -NH2 groups using the technique of self-assembled monolayers (SAM), and diatom cells were subsequently cultured on these surfaces. When the samples were rinsed after the adhesion of the diatom cells on the modified surfaces, the diatoms formed two dimensional arrays; this was not possible without the rinsing treatment. Furthermore, we examined the number of cells that grew and their motility by time-lapse imaging in order to clarify the interaction between the cells and SAMs. We hope that our results will be a basis for developing biodevices using living photosynthetic diatom cells.

Proposal of a Twin Aarginine Translocator System-Mediated Constraint against Loss of ATP Synthase Genes from Nonphotosynthetic Plastid Genomes

Organisms with nonphotosynthetic plastids often retain genomes; their gene contents provide clues as to the functions of these organelles. Yet the functional roles of some retained genes-such as those coding for ATP synthase-remain mysterious. In this study, we report the complete plastid genome and transcriptome data of a nonphotosynthetic diatom and propose that its ATP synthase genes may function in ATP hydrolysis to maintain a proton gradient between thylakoids and stroma, required by the twin arginine translocator (Tat) system for translocation of particular proteins into thylakoids. Given the correlated retention of ATP synthase genes and genes for the Tat system in distantly related nonphotosynthetic plastids, we suggest that this Tat-related role for ATP synthase was a key constraint during parallel loss of photosynthesis in multiple independent lineages of algae/plants.

Sequential valve development in the monoraphid diatom Achnanthes minutissima var. saprophila.

Valve development has been examined in Achnanthes minutissima var. saprophila H. Kobayasi & Mayama. The formation of the raphid valve (RV) proceeds in the same sequence as has previously been described for Navicula. Early development of the araphid yalve (AV) is remarkably similar to that of the RV, in that a primary central rib and primordial central nodule are initiated, followed by the development of secondary arms from the centre and the recurring of the primary rib at the poles. Therefore raphe slits appear both at the centre and poles during the early development of the AV. However, thin fin-like depositions arise along the primary central rib between the secondary arms extending out from the centre and the centripetal extensions of the primary central rib recurring from the poles. The fins then fuse with the secondary arms and the in-turned primary central rib, so that the initially-formed raphe slits do not develop any further and are filled in: an axial area devoid of a raphe is thus formed. The ...

Host-symbiont associations of polycystine Radiolaria: epifluorescence microscopic observation of living Radiolaria

Abstract In all 29 polycystine radiolarian species were obtained from surface seawater on May 28, 1999, using a plankton-net at one station (Site 990528; 26°37′18″N, 127°47′35″E) approximately 5 km northwest of Okinawa Island, Japan. In most polycystine radiolarians of the orders Nassellarida and Spumellarida symbiotic algae were observed under light microscopy. The light microscopic (LM) images of the symbionts, however, varied in clarity among individuals because of the variations in microanatomy of the host radiolarian cells. On the other hand, epifluorescence microscopic (EFM) observation easily detected and confirmed the existence of the algal symbionts within the host cytoplasm even in radiolarians such as Dictyocoryne truncatum (Ehrenberg) that include algal symbionts in the depth of the cytoplasm. The chloroplasts of the algal symbionts emitted autofluorescence in ultraviolet irradiation and they appeared red. That is, the autofluorescence images of the chloroplasts can be used to recognize the existence of the algal symbionts within the host radiolarians. Moreover, staining of the symbiont cells with 4′,6-diamido-2-phenylindle permitted visualization of the nucleus in the center of the symbiont cell, confirming the existence of living endosymbiotic algae within the polycystine radiolarians. Both the LM and EFM observations of eight polycystine radiolarian species revealed the specific patterns of various host-symbiont associations. (1) The investigated polycystine radiolarians all possess algal symbionts, except for one species, i.e. Dictyocoryne profunda Ehrenberg. (2) The size of the algal symbionts depends on the radiolarian species. The symbionts are largely classified into two types based on the size of their diameters, i.e. about 8–10 μm for the larger group and about 5 μm for the smaller one. (3) The algal symbionts show a variety of locations within the host radiolarian cytoplasm. The types of distribution of algal symbionts may be a useful characteristic for radiolarian taxonomy.

Multiple losses of photosynthesis in Nitzschia (Bacillariophyceae)

In order to obtain insights into the evolution of colorless (apochlorotic) diatoms, we investigated newly established apochlorotic strains of Nitzschia spp. using light and electron microscopy and molecular phylogenetic analyses. Fluorescence microscopic observations demonstrated that the apochlorotic diatoms lack chlorophylls. Transmission electron microscopy of two apochlorotic strains also demonstrated that their plastids lacked thylakoids; instead, having four‐membrane‐bound organelles without thylakoids, similar to nonphotosynthetic plastid remnants. From the apochlorotic strains, we also found plastid small subunit rRNA genes that were unusually long branched in phylogenetic analyses, as observed in other nonphotosynthetic plastids. Molecular phylogenetic analysis of the nucleus‐encoded large subunit rRNA genes showed eight distinct lineages for apochlorotic diatoms. The eight apochlorotic lineages were not monophyletic, suggesting that the loss of photosynthesis took place multiple times independently within Nitzschia. Several diatoms, including Nitzschia spp., are mixotrophic, which is an expected mode of nutrition that would help explain the evolutionary switch from a photosynthetic lifestyle to a heterotrophic lifestyle.

Two-dimensional trajectory analysis of the diatom Navicula sp. using a micro chamber

We describe a trajectory analysis of diatom cell locomotion by combining a micro chamber and two-dimensional position coordinate analysis. By shutting cells in a micro chamber, continuous microscopic observation of Navicula sp. cells was possible. The trajectory of each cell was visualized once every second by using position coordinate analysis although time resolution of previous papers were range of minutes. Our data revealed frequent change of movement direction. Furthermore, the correlation between the distances moved, the velocity, and the acceleration of the cells was discussed in detail.