Effects of Two Potential Allelochemicals on the Photosystem II of <i>Nitzschia closterium</i> and<i> Monostroma nitidum</i>

In aquaculture, high-density seaweed farming brings higher economic benefits but also increases outbreaks of diatom felt. The effective control of diatom felt in high-density seaweed farming has always been a research hotspot.This study selected two potential allelochemicals 2-hydroxycinnamic acid and quinic acid to explore their effectson a diatom Nitzschia closterium and an economic seaweed Monostroma nitidum. The results showed that2-hydroxycinnamic acid had better inhibitory effects than quinic acid on the growth, pigment content and photosynthetic efficiency of N. closterium. Their half-maximal inhibitory concentrations at 120 h (IC_{50–120 h}) were0.9000 and 1.278 mM, respectively. Additionally, these allelochemicals had limited inhibitory effects on thegrowth, pigment content and photosynthetic efficiency of M. nitidum before 24 h. To further explore the allelopathic effect of these chemicals, this study focused on the photosystem II energy fluxes of N. closterium. It wasfound that 3 mM 2-hydroxycinnamic acid could destroy the whole photosynthetic system by devastating the PSIIreaction centre (RC) before 24 h; however, the same concentration of quinic acid could only down-regulate theelectron transport efficiency by changing the effective antenna size of an active RC and downregulating the PSIIreaction centre density. These experimental results are expected to provide a new strategy to control diatom feltblooms on the high-density seaweed farming areas.     

PHYSIOLOGICAL CHARACTERIZATION OF SIX LIPID-PRODUCING DIATOMS FROM THE SOUTHEASTERN UNITED STATES1

Six strains of diatoms from intertidal waters were isolated as part of the SERI Aquatic Species Program collection and screening effort: Amphiprora hyalina Greville, Cyclotella cryptica Reimann, Lewin & Guillard, Navicula acceptata Hustedt (two strains, NAVIC6 and NAVIC8), Navicula saprophila Lange-Bertalot & Bonik, and Nitzschia dissipata (Kütz.) Grunow. Among numerous algal strains isolated as part of this collection effort, these six strains showed rapid growth and elevated lipid content in preliminary screening experiments and were chosen for further physiological characterization. N. dissipata grew most rapidly at 25°C, whereas the other five strains grew best at 30–35°C. Salinity tolerance varied among strains, with maximal growth occurring at the following conductivities: 10–60 mS.cm^?1 (A. hyalina and N. acceptata NAVIC8), 10–35 mS.cm^?1 (C. cryptica), 20–45 mS.cm^?1 (N. acceptata NAVIC6), 10 mS.cm^?1 (N. saprophila), and 20–35 mS.cm^?1 (N. dissipata). The diatoms also differed in their utilization of nitrogen sources with A. hyalina growing optimally with either nitrate or urea; N. acceptata NAVIC6, with either nitrate or ammonium; C. cryptica, N. acceptata NAVIC8, and N. dissipata, with nitrate; and N. saprophila, with urea. Under optimal conditions, A. hyalina grew at 2.0 doublings. day^?1; C. cryptica grew at 3.0 doublings. day^?1. Each Navicula strain had a growth rate of 3.8 doublings. day^?1, and N. dissipata grew at 2.6 doublings.day^?1. All six strains had lipid contents in excess of 37% ashfree dry weight (AFDW) under nutrient-limited conditions, with N. saprophila having the highest lipid content at 48% AFDW.     

MORPHOLOGY OF THE MARINE DIATOM NITZSCHIA NAVIS-VARINGICA, SP. NOV. (BACILLARIOPHYCEAE), ANOTHER PRODUCER OF THE NEUROTOXIN DOMOIC ACID

A new marine diatom, Nitzschia navis-varingica , sp. nov., isolated from Vietnamese waters, is described by light, transmission, and scanning electron microscopy, including thin sectioning. The new species has been found to produce the neurotoxin domoic acid (DA), better known from several species of Pseudo-nitzschia Peragallo and one species of Amphora Ehrenberg. Production of DA is therefore more widespread among diatoms than previously thought. Taxonomically, the genus Nitzschia Hassall is exceptionally difficult, with about 900 described taxa. Grunow (in Cleve and Grunow 1880 divided the genus into 24 sections, and this system is still used with modifications. Nitzschia navis-varingica , sp. nov. fits best into a group of sections that includes Dubiae, Bilobatae , most of the Lanceolatae , and Lineares , all sensu Grunow, as the cell is slightly indented in the middle in girdle view and has a moderately eccentric raphe and a weak longitudinal fold on the valve. Many species within these sections have features similar to N. navis-varingica , but no species seems to be identical. Because both Pseudo-nitzschia and Nitzschia belong to the family Bacillariaceae, it seems reasonable to look for further producers of DA in this family, including freshwater species, which mainly comprise species within the sections Dubiae, Bilobatae, Lanceolatae , and Lineares.     

Does irradiance influence the tolerance of marine phytoplankton to high pH?

The effect of irradiance on the tolerance to high pH of the two marine protists Heterocapsa triquetra and Nitzschia navis-varingica were investigated by conducting a series of pH drift experiments. In order to select appropriate levels of irradiance for the pH drift experiments, the photosynthetic activity and the growth rates of the two species were investigated at irradiances from 5 to 250 µmol photons m^-2 s^-1. Irradiances of 20, 35, 80 and 250 µmol photons m^-2 s^-1 were subsequently selected for further studies, because they represented conditions from severely light limited to fully light saturated with respect to photosynthesis and growth. At all four light levels, the pH limits for growth were 9.29-9.42 for H. triquetra and 9.54-9.77 for N. navis-varingica. The pH limit for growth was not positively correlated to irradiance in either of the species. We therefore conclude that low light does not reduce the pH tolerance of the protists studied.     

ECOLOGICAL CONSIDERATIONS OF DIATOM CELL MOTILITY. I. CHARACTERIZATION OF MOTILITY AND ADHESION IN FOUR DIATOM SPECIES1

To better determine the ecological role of motility in pennate diatoms, we quantitatively characterized several motility and adhesion properties of four species of motile pennate diatoms (Craticula sp., Pinnularia sp., Nitzschia sp., and Stauroneis sp.) isolated from the same freshwater pond. Using computer-assisted video microscopy, we measured speed, size/shape, functional adhesion, path curvature, and light sensitivity for these species, each of which shows a distinctive set of motile behaviors. The average speeds of Stauroneis, Pinnularia, Nitzschia, and Craticula cells are 4.6, 5.3, 10.4, and 10.0 μm · s^?1, respectively. Craticula and Nitzschia cells move in a relatively straight path (<4 degrees rotation per 100 μm movement), Stauroneis exhibits minor rotation (about 7 degrees per 100 μm movement), and Pinnularia rotates considerably during movement (about 22 degrees per 100 μm moved). Functional adhesion (as measured by the release rate of attached cells from the underside of an inverted coverslip) shows a half time for cell release of approximately 50 min for Craticula, 192 min for Pinnularia, and >1 day for Nitzschia and Stauroneis. Direction reversal at light/dark boundaries, which appears to be the main contributor to diatom Phototaxis, is most responsive for Craticula, Pinnularia, and Nitzschia at wavelengths around 500 nm. Craticula and Nitzschia cells are the most sensitive in the photophobic response, with over 60% of these cells responding to a 30-1x light/dark boundary at 500 nm, whereas Pinnularia cells are only moderately responsive at this irradiance, showing a maximal response of approximately 30% of cells at 450 nm. Stauroneis cells, in contrast, had a maximal photosensitive response at 700 nm, suggesting that this cell type may use a different response mechanism than the other three cell types. In addition, Craticula and Pinnularia show a net movement out of the light spot when illuminated at 650 nm, whereas Stauroneis shows a net movement out of the light spot when illuminated at 450 nm. Such quantitative characterizations of species-specific responses to environmental stimuli should give us a firm foundation for future studies analyzing the behavior of interspecies diatom competition for limited light or nutrient resources.     

Heterotrophic production of eicosapentaenoid acid by the diatom Nitzschia laevis: effects of silicate and glucose

The effects of silicate and glucose on growth and eicosapentaenoic acid (EPA) production by the diatom Nitzschia laevis were studied. By alternately altering the concentrations of silicate (2.7–64 mg l⁻¹) and glucose (1–40 g l⁻¹) in the medium, the highest cell dry weight (ca. 5.5 g l⁻¹) was obtained at 20 g l⁻¹ glucose and 32 mg l⁻¹ silicate, while the highest specific growth rate (ca. 0.65 day⁻¹) was obtained at a relatively low glucose concentration (5 g l⁻¹) and high silicate concentrations (32–64 mg l⁻¹). At glucose levels of 5 and 20 g l⁻¹, EPA content was higher with lower silicate concentrations (2.7 and 16 mg l⁻¹ silicate, respectively), while at a silicate level of 16 mg l⁻¹, higher glucose concentrations (20–40 g l⁻¹) facilitated EPA formation. The highest EPA yield (131 mg l⁻¹) was obtained at 20 g l⁻¹ glucose and 32 mg l⁻¹ silicate, while the highest EPA productivity (15.1 mg l⁻¹ day⁻¹) was obtained at 20 g l⁻¹ glucose and 64 mg l⁻¹ silicate. Journal of Industrial Microbiology & Biotechnology (2000) 25, 218–224. Received 08 May 2000/ Accepted in revised form 21 July 2000     

VALVE MORPHOGENESIS AND THE MICROTUBULE CENTER IN THREE SPECIES OF THE DIATOM NITZSCHIA1

The relationship of cell organelles to valve morphogenesis was investigated in three species of Nitzschia. One, N. sigmoidea (Nitzsch) W. Sm., showed consistent ability to generate both nitzschioid and hantzschioid symmetry in daughter cells following cytokinesis; the other two maintained nitzschioid symmetry stably. From previous work with Hantzschia, a certain sequence of events could be anticipated in the cytoplasm. In two significant areas–the behavior of the Microtubule Center (MC) and its microtubule (MT) system, and the central origin of the silicalemma–not only were the results unexpected, but the three species showed fundamental differences among themselves. In N. sigmoidea, the silicalemma (and the future raphe region) arises centrally on the cleavage furrow, and after some lateral expansion, the silicalemmas and their associated organelles move in opposite directions in daughter cells, so that the raphe and the raphe canals end up along the girdle side of the cell as expected. However, the MCs never become associated with their silicalemma, remaining throughout near the girdle bands. In N. sigma (Kütz) W. Sm., the silicalemmas arise centrally and after lateral growth, move in opposite directions to generate nitzschioid symmetry. In this case, the MCs move to the vicinity of but never close to the silicalemmas, and follow them distantly during their lateral movement. In N. tryblionella Hantzsch, the new silicalemmas arise opposite one another, on one side of the daughter cells; each MC soon moves very close to its silicalemma, and remains thus through most of valve morphogenesis. Later, only one silicalemma/MC complex moves laterally, establishing the nitzschioid symmetry in both daughter cells. In all three species, as in Hantzschia, linear arrays of mitochondria aligned along MTs occupy the forming raphe canal, and microfilaments line the outer edge of the expanding silicalemma. The fibulae (the wall struts arching across the raphe canal) in Hantzschia always grow from the valve surface to the girdle surface of the forming valves. In these three Nitzschiae, this invariably happens in only one daughter cell of any pair; in the other, all the fibulae grow from the girdle surface to the valve surface. An explanation of these variations is proposed: that the morphogenetic machinery of Nitzschia and Hantzschia have a common origin, with present Nitzschiae having undergone considerable diversification at the intracellular level, causing the unstable cell symmetry exhibited by several modern species. Perhaps a taxonomic distinction between Hantzschia and Nitzschia lies in whether the morphogenetic machinery associated with valve morphogenesis moves laterally in the same or in opposite directions.     

山西省盐池硅藻一新种

运城菱形藻 新种 图版1,图1—10 Nitzschia yunchengensis Xie et Li, sp. nov. Frustula e facie connexionis rectangularis, angulis rotundatis, marginibus in mediomodice concavis, axibus pervalvaribus 9. 3—10. 03μm altis, copulis multis. Valvae lineares,     

First account of apochlorotic diatoms from mangrove waters in Florida

ABSTRACT. From January to December 2004, monthly samples were collected from the mangrove salt marsh of J.U. Lloyd State Park, Florida, to examine the spatial and temporal distributions of heterotrophic diatoms in this subtropical region. Four non-pigmented (i.e. apochlorotic), heterotrophic diatom morphotypes were isolated from mangrove neuston and plankton sites. Colorless diatoms were numerically significant in neuston during the fall and winter months and counts peaked at 174 × 10³ cells/L in December. Heterotrophic diatoms were most prevalent in mangrove plankton in October and averaged 55.5 × 10³ cells/L. Valve morphology was detailed for mangrove morphotypes (I, II, V, and VI). However, only one type (I) was named with confidence ( Nitzschia leucosigma ). The other three types failed to conform closely to published diagnostic features suggesting that either characters are more variable than accepted or these types were new species. Growth responses to changes in salinity and irradiance were detailed in the laboratory. All morphotypes were euryhaline, tolerating salinities between 10‰ and 40‰; N. leucosigma was most salt tolerant and grew from 10‰ to 60‰. Maximum growth was achieved between 20‰ and 40‰. Growth was not significantly different for heterotrophic diatoms during light and dark treatments or for diatoms grown with or without bacteria.