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.     

Underwater locomotion strategy by a benthic pennate diatom Navicula sp.

The mechanism of diatom locomotion has been widely researched but still remains a hypothesis. There are several questionable points on the prevailing model proposed by Edgar, and some of the observed phenomena cannot be completely explained by this model. In this paper, we undertook detailed investigations of cell structures, locomotion, secreted mucilage, and bending deformation for a benthic pennate diatom Navicula species. According to these broad evidences, an updated locomotion model is proposed. For Navicula sp., locomotion is realized via two or more pseudopods or stalks protruded out of the frustules. The adhesion can be produced due to the pull-off of one pseudopod or stalk from the substratum through extracellular polymeric substances. And the positive pressure is generated to balance the adhesion because of the push-down of another pseudopod or stalk onto the substratum. Because of the positive pressure, friction is generated, acting as a driving force of locomotion, and the other pseudopod or stalk can detach from the substratum, resulting in the locomotion. Furthermore, this model is validated by the force evaluation and can better explain observed phenomena. This updated model would provide a novel aspect on underwater locomotion strategy, hence can be useful in terms of artificial underwater locomotion devices.     

Sexual auxosporulation of the marine diatom Navicula directa var. directa

Sexual auxosporulation was observed in a mixed culture of two strains of Navicula directa var. directa. Two gametes did not re‐arrange in their gametangium and each adhered to the inner surfaces of the gametangial theca. Each of the two gametes of one gametangium fused with a gamete of the other gametangium iso‐gamously. As a result, two zygotes and hence two auxo‐spores were produced per paired gametangia. As the gametangial thecae kept close to the gametes during fusion, the zygote became associated with two different thecae. The presence of type IB2a of Geitler's (1973) system was confirmed by the present observations.     

Heterotrophic nutrition of the marine pennate diatom Navicula pavillardi Hustedt.

Navicula pavillardi Hustedt, a marine, littoral, pennate diatom, can grow in the dark on glutamate or on the complex organic supplements tryptone or yeast extract. Growth on glutamate in the dark took place without an initial lag phase, whereas growth on tryptone began only after a 2-day lag phase that could be abolished by the simultaneous presence of glucose. Lactate inhibited growth in the dark on glutamate, but not photoautotrophic growth. Relatively low concentrations of glutamine inhibited photoautotrophic growth. The observed doubling time for heterotrophic growth on glutamate or tryptone was about 70 h, compared with a doubling time of 24 h under optimal photoautotrophic conditions. Glucose did not decrease the doubling time in the dark on tryptone. The assimilation efficiency for glutamate was 41%. The estimated necessary uptake rate for glutamate to account for the observed heterotrophic doubling time on glutamate was close to those measured with isotope techniques. The kinetic parameters for glutamate uptake, which followed Michelis-Menten kinetics, were Ks = 0.018 mM, and Vmax = 7.0 X 10(-10) mumol per cell per minute. Although several amino acids served as sole nitrogen sources for photoautotrophic growth and were demonstrated by the use of isotope techniques to enter the cells, they could not be used as substrates for growth in the dark. Glucose was not taken up to a significant extent except by cells grown in the presence of tryptone. Lactate was taken up only by dark-grown cells. Results of preliminary studies on the metabolic fate of several uniformly labeled amino acids are presented.     

Sulfonic acid metabolism in the diatom Navicula pelliculosa

Sulfate uptake and the cellular levels of three sulfonic acids,cysteinolic acid, sulfopropanediol, and the plant sulfolipid,were followed using ³⁵S-sulfate labeled cells of the diatomNavicula pelliculosa in silicate starvation synchrony, sulfurdeficiency, and chase experiments. Sulfate uptake was nearly completely inhibited during silicatestarvation but was resumed 3 hr after silicate addition (synchronyinduction). Cysteinolic acid and sulfopropanediol levels decreasedrapidly after silicate addition, although an earlier decreasein cysteinolic acid was noted, possibly in response to sulfateuptake inhibition. No decrease in the sulfur-containing lipidswas noted. A metabolically active role for cysteinolic acid as a reservoirof reduced sulfur was indicated, relative to sulfopropanedioland the plant sulfolipid, on the basis of rapid utilizationand turnover during sulfur deficiency and chase experiments.It was suggested that sulfopropanediol was formed by a reductivedeamination of cysteinolic acid. ¹Present address: Department of Nutrition and Food Science,Massachusetts Institute of Technology, Cambridge, Massachusetts02139, U. S. A. (Received April 2, 1973; )     

Navicula endophytica Sp.Nov., A pennate diatom with an unusual mode of existence

The diatom Navicula endophytica sp. nov., first observed by Baardseth (1966) in the intercellular substance of receptacles of Ascophyllum nodosum, is described. The species has been encountered neither as an epiphyte on this seaweed nor as a planktonic form.     

Stable nuclear transformation of the diatom Chaetoceros sp.

A nuclear transformation system for the centric diatom Chaetoceros sp. has been established using two plasmids pTpfcp/nat and pTpNR/green fluorescent protein (GFP) that had been used for Thalassiosira pseudonana transformation. These contain the nourseothricin resistance gene (nat) with the fucoxanthin chlorophyll a/c binding protein (fcp) promoter/terminator from T. pseudonana and the enhanced green fluorescent protein gene (egfp), with the nitrate reductase (NR) promoter/terminator from T. pseudonana, respectively. Transformants were recovered in the presence of the antibiotic nourseothricin. One to four copies of both nat and egfp genes were integrated into genomic DNA of the transformants. Transformation efficiency was 1.5–6.0 transformants per 10⁸ cells. This work is the first report of stable genetic transformation of Chaetoceros, which is important as not only a constituent member of marine ecosystem but also feed for aquaculture.     

Taxonomic studies on the diatom genus Navicula Bory. Navicula grevillii (CA.Ag.) Heiberg and N. comoides (Dillwyn) H. & M. Peragallo

Two closely related species of the diatom genus Navicula were investigated using light and electron microscopy. A hitherto unrecorded structure associated with the raphe of N. delognei Van Heurck is described.
Examination of type material revealed that the nomenclatural types of N. grevillii (CA.Ag.) Heiberg and N. comoides (Dillwyn) H. & M. Peragallo do not agree with the present understanding of these species, therefore alternative names were sought. All the synonyms of each species were traced and a table of synonymy is supplied. The names N. delognei and N. pseudocomoides are proposed as replacements for N. grevillii and N. comoides respectively and types are cited.     

Continuous culture with deep seawater of a benthic food diatom Nitzschia sp.

A continuous culture system for a benthic food diatom Nitzschia sp. wasestablished by using properties of high nutrient and clean of deep seawater(DSW). DSW collected from 320 m depth in Muroto City, Japan, was introducedinto a glass-pipe bioreactor (14 cm length, 3 cm diam.) containing glassbeads of 0.5 cm diam. as substrata for the alga, and it was incubated at18°C · 80Em^–2sec^–1 · L:D=14:10. The chlorophyll a yield of benthicdiatoms in a reactor as a unit of surface area of the substratum was only0.001–0.003 g cm^–2 when the flow rate of DSW was 0(batch culture conditions). However, when DSW was supplied continuously to areactor, the yield increased to 1.4 g-chl.a cm^–2 alongwith the increase in flow rate of DSW. Moreover, amounts of chl.a washed outof the system were negligible, 0.0014 to 0.0045%, even though theflow rate of DSW was as much as 25 times h^–1, suggesting thatsloughing of benthic diatoms from the substratum was minimized. Although theyield of diatoms fluctuated significantly at the time that the DSW wascollected, the variation could be minimized by increasing the flow rate ofDSW. These results indicate that the continuous culturing system with DSWsupports the stable and effective mass culture of benthic food diatom.     

Stephanodiscus kusuensis, sp. nov a new Pleistocene diatom from Southern Japan

A new fossil diatom, Stephanodiscus kusuensis sp. nov., is described from a diatomite deposit from the Kusu Basin, Oita Prefecture Japan. Radiometric age estimates of the strata in which the taxon occurs are 400–500 kyr. The new species is distinct from all other known species of Stephanodiscus because it possesses a highly pronounced double concentric undulation and two distinct arrangements of central strutted processes. Cladistic analysis is used to identify the phylogenetic position of this taxon with respect to other Stephanodiscus species.     

Photosynthesis and respiration of a diatom biofilm cultured in a new gradient growth chamber

Abstract A diatom biofilm was grown in a chamber developed for culture of biofilms in chemical gradients. The diatoms grew on a polycarbonate membrane filter which separated a sterile reservoir, with added phosphate, from a reservoir without phosphate. Within 3 weeks of inoculation, a thick biofilm developed on the surface of the filter. The biofilms were homogeneous and therefore suitable for calculations of O₂ diffusion fluxes from concentration profiles of O₂. Profiles of O₂, pH, and gross photosynthesis at different light intensities and liquid medium concentrations of dissolved inorganic carbon and O₂ were measured with microelectrodes. Respiratory activity in a layer of the biofilm was determined as the difference between gross photosynthesis and outflux of O₂ from that layer. The photosynthetic activity in a well-developed biofilm grown at 360 μEinst m⁻² s⁻¹ and 2.4 mM HCO₃⁻ was limited by the supply of inorganic carbon. Exposure to light above 360 μEinst m⁻² s⁻¹ stimulated gross photosynthesis as well as respiratory processes without affecting net outflux of O₂. Higher concentrations of inorganic carbon, on the other hand, enhanced gross photosynthesis without concurrent increase in respiratory rate, resulting in an increased outflux of O₂. High concentrations of O₂ in the liquid medium decreased the net outflux of O₂ with little effect on the gross photosynthesis. The effects of inorganic carbon and O₂ on the metabolic activities of the biofilm were consistent with the presence of photorespiratory activity.     

Nitzschia cylindroformis sp. nov., a common and abundant nanoplankton diatom of the eastern subarctic Pacific

A new species of diatoms, intermediate between Nitzschia cylindrus(Grun.) Hasle and Nitzschia pseudonana Hasle is described. Differencesin morphology of the three species are outlined. The new specieshas been recorded only between 37°N and 53°N in thePacific Ocean while N. cylindrus is bipolar and N. pseudonanais cosmopolitan in distribution.     

Thalassiosira bulbosa Syvertsen,sp. nov., an arctic marine diatom

Summary Thalassiosira bulbosa Syvertsen is described from one clonal culture and natural marine, arctic material collected from brown spots on the ice and from seawater close to the ice border. The new taxon belongs to the group of Thalassiosira species with a single central strutted process and one marginal ring of strutted processes. Specific features are the conspicuous bulbshaped outer part of the marginal strutted processes and a strutted tube surrounded by two oblong, bean-shaped satellite pores. T. bulbosa forms resting cells differing from the vegetative cells mainly in the degree of silicification and by having fewer openings through the frustule. The species may obtain its maximal cell size by a purely vegetative auxospore formation.     

Changes in eicosapentaenoic acid content of Navicula saprophila, Rhodomonas salina and Nitzschia sp. under mixotrophic conditions

Three species of microalgae able to produce eicosapentaenoic acid(EPA) were collected from brackish and sea water around Japan. The species were identified as Navicula saprophila, Rhodomonassalina and Nitzschia sp. EPA as a proportion of total fatty acids increased in the presence of acetic acid for Rhodomonas salina and Nitzschia sp. However, Navicula saprophila displayed the greatest productivity of EPA and the EPA content of its biomass was enhanced under mixotrophic conditions in the presence of acetic acid. This revised version was published online in August 2006 with corrections to the Cover Date.     

A description of glucose uptake in Navicula pelliculosa (Breb) hilse including a brief comparison with an associated Flavobacterium sp.

Archives of Microbiology - Navicula pelliculosa and an associated Flavobacterium sp. were isolated from the epiphyton of Scirpus maritimus, an emergent macrophyte growing in a brackish drainage...