Shooting of sporidium by "gun" cells in <Emphasis Type="Italic">Haptoglossa heterospora</Emphasis> and <Emphasis Type="Italic">H. zoospora</Emphasis> and secondary zoospore formation in <Emphasis Type="Italic">H. zoospora</Emphasis>

Haptoglossa spp. (Lagenidiales, Oomycetes) have been known to parasitize microscopic animals by means of a "gun" cell that shoots an infection cell, named the sporidium, into the body of the animal. A thallus grown from the sporidium changes into a zoosporangium at maturation to produce a number of zoospores that encyst after a swarming period, and the resulting cysts germinate to produce gun cells. In Haptoglossa zoospora, endoparasitic in nematodes, the cysts of primary zoospores that swam for about 5 min did not develop gun cells but produced secondary zoospores that swam for about 3 h. After encystment of the secondary zoospores, each secondary cyst germinated to produce a gun cell. In the present study, the secondary zoospores of the genus Haptoglossa could be recorded with a videocassette recorder for the first time. The videocassette recording also revealed the infection of a nematodes by H. zoospora and H. heterospora to be composed of two steps of injection of a sporidium by the gun cell, in which the gun cell came in contact with the cuticle of a nematode and produced a spherical adhesorium on the tip of the cell in 0.07–0.1 s in both species. The adhesorium was ∼2 μm in H. zoospora and ∼4 μm in H. heterospora. When the adhesorium infiated to full size, it shot the sporidium into the nematode's body in 0.5–0.65 s and in 0.2–0.5 (or rarely 1.0) s in H. zoospora and H. heterospora, respectively. After shooting, the empty gun cell with an empty cyst case was separated from the cuticle immediately in both species. Received: October 3, 2001 / Accepted: December 13, 2001     

A novel growth-promoting protein in the conditioned media from the rotifer <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> at an early exponential growth phase

We confirmed the existence of growth-promoting substances in the conditioned media (CM) from the rotifer Brachionus plicatilis at an early exponential growth phase and isolated a novel protein with a growth-promoting activity from the crude extract (CE) of rotifer cells. CM was prepared from the culture media where rotifers had been cultured at an early exponential growth phase and filtered through a 0.22-μm filter membrane. The growth-promoting activity was determined using rotifers in CM for 5 days. As a result, the increase of rotifers added with CM was significantly higher than that of the control in artificial seawater (P < 0.001). Moreover, the growth-promoting activity of CM was dose-dependent and inactivated by heat treatment at 80°C for 60 min. Meanwhile, CM filtered through a <10 kDa ultrafiltration membrane showed a low activity, whereas proteinase K treatment resulted in a complete inactivation. These results suggest that the rotifer secrets growth-promoting proteins into CM. CE also contained a protein with the activity and properties similar to those found in CM. Then, CE was subjected to purification of a growth-promoting protein for convenience using various types of chromatography after fractionation with 30–80% saturated ammonium sulfate. Subsequently, a protein with an approximate molecular weight of 25000 was isolated, and its N-terminal amino acid sequence was determined to be PAVVDFTAVWFGPLQMIKP. An orthologue was found in the EST database of B. plicatilis, the full sequence of which showed about 50% identity to the corresponding regions of thioredoxins from other organisms.     

The diversity of bacteria,eukaryotic cells and viruses in an oligotrophic lake

An in situ transmission electron microscopic study of biomass samples concentrated from oligotrophic lake water revealed a variety of virus-infected microbial cells and many free viruses and virus-like particles. The most abundant group of microorganisms in screened and filtered water-column samples were 2 μm or less in diameter, and included representatives of several oligotrophic genera, Prosthecomicrobium, Ancyclobacter, Caulobacter and Hyphomicrobium. Among the prokaryotic host cells, which included both heterotrophs and autotrophs, on the basis of electron microscope observations, approximately 17% were infected with bacteriophage or bore adherent phage particles on their surfaces. Several bacterial morphotypes were observed among the prokaryotic hosts. Water samples passed through a 20-μm Nitex screen allowed us to concentrate and examine the larger host cells as well, including several species of single-celled algae and two amoeba species. The infected algal cells included those Chlorella-like in appearance, photosynthetic flagellates and others that could not be positively identified. About one-third of the eukaryotic cells were infected by viruses that were larger (150–200 nm) and structurally more complex than bacteriophages (50–60 nm). None of the viruses have been isolated, but when 0.2 μm filtrate from a biomass sample was spotted onto lawns of four representative heterotrophs and a Chlorella, the clearing observed was taken as evidence of lysis. Cyanobacterial lawns showed no plaques. Thin sections of two amoeba showed food vacuoles containing what appeared to be virus particles of a type seen in certain prokaryotic and eukaryotic cells in the biomass. Received: 26 January 1996 / Received revision: 10 July 1996 / Accepted: 5 August 1996     

Optimization of protoplast yields from the red algae <Emphasis Type="Italic">Gracilaria dura</Emphasis> (C. Agardh) J. Agardh and G. <Emphasis Type="Italic">verrucosa</Emphasis> (Huds.) Papenfuss

This study reports on the optimization of protoplast yield from two important tropical agarophytes Gracilaria dura and Gracilaria verrucosa using different cell-wall-degrading enzymes obtained from commercial sources. The conditions for achieving the highest protoplast yield was investigated by optimizing key parameters such as enzyme combinations and their concentrations, duration of enzyme treatment, enzyme pH, mannitol concentration, and temperature. The significance of each key parameter was also further validated using the statistical central composite design. The enzyme composition with 4% cellulase Onozuka R-10, 2% macerozyme R-10, 0.5% pectolyase, and 100 U agarase, 0.4 M mannitol in seawater (30‰) adjusted to pH 7.5 produced the highest protoplast yields of 3.7 ± 0.7 × 10⁶ cells g⁻¹ fresh wt for G. dura and 1.2 ± 0.78 × 10⁶ cells g⁻¹ fresh wt for G. verrucosa when incubated at 25°C for 4–6 h duration. The young growing tips maximally released the protoplasts having a size of 7–15 μm in G. dura and 15–25 μm in G. verrucosa, mostly from epidermal and upper cortical regions. A few large-size protoplasts of 25–35 μm, presumably from cortical region, were also observed in G. verrucosa.     

Pigmented Nanoflagellates Grazing on <Emphasis Type="Italic">Synechococcus</Emphasis>: Seasonal Variations and Effect of Flagellate Size in the Coastal Ecosystem of Subtropical Western Pacific

We investigated seasonal variation of grazing impact of the pigmented nanoflagellates (PNF) with different sizes upon Synechococcus in the subtropical western Pacific coastal waters using grazing experiments with fluorescently labeled Synechococcus (FLS). For total PNF, conspicuous seasonal variations of ingestion rates on Synechococcus were found, and a functional response was observed. To further investigate the impact of different size groups, we separated the PNF into four categories (<3, 3–5, 5–10, and >10 μm). Our results indicated that the smallest PNF (<3 μm PNF) did not ingest FLS and was considered autotrophic. PNF of 3–5 μm in size made up most of the PNF community; however, their ingestion on Synechococcus was too low (0.1–1.9 Syn PNF⁻¹ h⁻¹) to support their growth, and they had to depend on other prey or photosynthesis to survive. The ingestion rate of the 3–5 μm group exhibited no significant seasonal variation; by contrast, the ingestion rates of 5–10 and >10 μm PNFs showed significant seasonal variation. During the warm season, 3–5 μm PNF were responsible for the grazing of 12% of Synechococcus production, 5–10 μm PNF for 48%, and >10 μm PNF for 2%. Taken together, our results demonstrate that the PNF of 3–10 μm consumed most Synechococcus during the warm season and exhibited a significant functional response to the increase in prey concentration.     

Photoreceptor ultrastructure in the Antarctic mussel shrimp Acetabulastoma (Crustacea; Ostracoda), a parasite of Glyptonotus antarcticus (Crustacea; Isopoda)

The ultrastructure of the nauplius eye of the tiny Antarctic ostracode Acetabulastoma sp. is described and conclusions about its possible function are drawn. Each of the three eye-cups measures approximately 20 μm in diameter and is optically isolated from its neighbour by screening pigments, which are contained in pigment cells behind a tapetum of concentrically arranged, ca. 1-μm-long and 0.1-μm-thick, crystals. Three and sometimes four separate rhabdoms with microvilli measuring 50–60 nm in diameter project from the concave side of the tapetum up to 5 μm deep into the eye-cup interior, which is filled by the retinula cell bodies with their spherical nuclei and various organelles. Desmosomes and microtubules are seen and light-induced cell or membrane damage was minimal. The observations suggest that the Acetabulastoma eye has photoreceptors that can tolerate an exposure to bright light and it may be used to inform its owner of the approach of danger, the depth of water, and/or the season. Accepted: 27 August 1998     

Selective feeding by larvae of the crown-of-thorns starfish, Acanthaster planci (L.)

 The effect of phytoplankton size on feeding rates of planktonic larvae of the crown-of-thorns starfish Acanthaster planci (L.) was evaluated by examining their gut contents under an epifluorescence microscope. Concentrations of coccoid cyanobacteria in natural seawater ranged between 1.73 and 5.33×10⁵ cells ml^-1 and were three to four orders of magnitude greater than that of eukaryotes. Under these conditions, A. planci larvae ingested similar or smaller numbers of cyanobacteria than eukaryotes. Consequently, clearance rates of A. planci larvae on cyanobacteria were approximately three orders of magnitude lower than those on eukaryotes. Cyanobacteria and eukaryotes in the gut of A. planci larvae had mean equivalent spherical diameters (ESD) of 1–2 μm and 3.6–4.6 μm, respectively. Thus, the volume of cyanobacteria ingested was less than 10% of the volume of eukaryotes ingested. Acanthaster planci larvae were fed cultured phytoplankton Dunaliella tertiolecta and suspensions of three different sizes of plastic beads with fluorescence labelling. There was no significant difference in clearance rates on 6 and 20 μm plastic beads. Clearance rates on 1 μm plastic beads were, however, much lower than those on 6 and 20 μm plastic beads. Clearance rates of A. planci larvae on D. tertiolecta (ca. 5 μm ESD) were significantly higher than those on 6 and 20 μm plastic beads. Apart from particle size, this result shows that feeding of A. planci larvae is influenced by other properties of potential food particles. Accepted: 24 May 1996     

Development of Heavy Metal-Resistant Mutants of Phosphate Solubilizing <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. NBRI 4014 and Their Characterization

Pseudomonas sp. NBRI 4014 is a potent phosphorus solubilizer (284 μg/ml). It also produced significant levels of siderophore (143.87 μg/ml) and IAA (5.6 μg/ml). Siderotyping indicated it was P. aeruginosa siderovar 1. Cadmium (180 μM), nickel (420 μM), and chromium (370 μM) resistant mutants were developed and characterized for their PGPR properties. Mutants were stable under non-selective pressure. In cases of nickel and cadmium, there were reductions of the siderophore levels. However, they were able to promote root and shoot elongation in soybeans (Glycine max PK 564) at a significant level (p < 0.05) in the presence of metals unfamiliar to the wild type. The persistence and stability of mutants were evident in rhizospheric soil, thus their exploitation for polluted/contaminated sites was supported. Received: 27 December 2001 / Accepted: 28 January 2002     

Optimization of culture conditions for determining hepatobiliary disposition of taurocholate in sandwich-cultured rat hepatocytes

Summary This study was undertaken to examine the influence of time and volume of collagen overlay, type of media, and media additives on taurocholate (TC) accumulation and biliary excretion in hepatocytes cultured in a collagen-sandwich configuration. Hepatocytes were isolated from male Wistar rats by in situ perfusion with collagenase, seeded onto collagencoated 60-mm dishes, overlaid with gelled collagen, and cultured for 4 d. Experiments to examine the influence of time and volume of collagen overlay were conducted in Dulbecco's modified Eagle's medium (DMEM)+1.0μM dexamethasone (DEX)+5% fetal bovine serum (FBS). Hepatocytes were overlaid at 0 h with 0.1 or 0.2 ml collagen, or at 24 h with 0.1 or 0.2 ml collagen. The influence of media type and additives was examined in hepatocytes overlaid at 0 h with 0.2 ml collagen and incubated in DMEM+0.1μM DEX, DMEM+0.1μM DEX+5% FBS, Williams' medium E+0.1μM DEX+1% ITS^Θ+, DMEM +1.0μM DEX, DMEM+1.0 μM DEX+5% FBS, or modified Chee's medium (MCM)+0.1 μM DEX+1% ITS^Г+. [³H] TC accumulation by hepatocytes in Hank's balanced salt solution (HBSS) and Ca²⁺-free HBSS was measured, and the biliary-excretion index (BEI: percentage of accumulated TC localized in the canalicular compartment) was calculated. Light microscopy and carboxydichlorofluorescein fluorescence were employed to examine the cellular and canalicular morphologies. The volume of collagen used for both the substratum and the overlay did not affect TC accumulation or biliary excretion. The BEI tended to be higher in cells overlaid at 24 h (BEI=0.649 [0.1 ml collagen]; BEI=0.659 [0.2 ml collagen]) compared with those overlaid at 0 h after seeding (BEI=0.538 [0.1 ml collagen]; BEI=0.517 [0.2 ml collagen]), although the differences were not statistically significant. Hepatocytes cultured in MCM produced consistently the lowest BEI of TC (BEI=0.396). Differing DEX concentration (0.1 μM versus 1.0 μM) with or without 5% FBS did not appear to have a significant effect on the BEI of TC.     

Photosynthetic performance of regenerated protoplasts from disintegrated cells of <Emphasis Type="Italic">Bryopsis hypnoides</Emphasis> (Chlorophyta)

The photosynthetic performances of regenerated protoplasts of Bryopsis hypnoides, which were incubated in seawater for 1, 6, 12, and 24 h, were studied using chlorophyll (Chl) fluorescence and oxygen measurements. Results showed that for the regenerated protoplasts, the pigment content, the ratios of photosynthetic rate to respiration rate, the maximal photosystem II (PSII) quantum yield (F_v/F_m), and the effective PSII quantum yield (Φ_PSII) decreased gradually along with the regeneration progress, indicated that during 24 h of regeneration there was a remarkable reduction in PSII activity of those newly formed protoplasts. We assumed that during the cultivation progress the regenerated protoplasts had different photosynthetic vigor, with only some of them able to germinate and develop into mature thalli. The above results only reflected the photosynthetic features of the regenerated protoplasts at each time point as a whole, rather than the actual photosynthetic activity of individual aggregations. Further investigation suggested a relationship between the size of regenerated protoplasts and their viability. The results showed that the middle-sized group (diameter 20–60 μm) retained the largest number of protoplasts for 24 h of growth. The changes in F_v/F_m and Φ_PSII of the four groups of differently sized protoplasts (i.e. < 20, 20–60, 60–100, and > 100 μm) revealed that the protoplasts 20–60 μm in diameter had the highest potential activity of the photosynthetic light energy absorption and conversion for several hours.     

Volatilization of Mercury by Immobilized Bacteria (Klebsiella pneumoniae) in Different Support by Using Fluidized Bed Bioreactor

Klebsiella pneumoniae, a mercury-resistant bacterial strain able to reduce ionic mercury to metallic mercury, was isolated from wastewater of Casablanca. This strain exhibits high minimal inhibition concentrations for heavy metals such as mercury 2400 μM, lead 8000 μM, silver 2400 μM, and cadmium 1000 μM. This bacterium was immobilized in alginate, polyacrylamide, vermiculite, and cooper beech and was used for removing mercury from a synthetic water polluted by mercury by using a fluidized bead bioreactor. Immobilized bacterial cells of Klebsiella pneumoniae could effectively volatilize mercury and detoxify mercury compounds. Moreover, the efficiency of mercury volatilization was much greater than with the native cells. The highest cleanup and volatilization rates were obtained when Klebsiella pneumoniae was entrapped in alginate beads, with a cleanup rate of 100% and a volatilization rate of 89%. Immobilized cells in alginate continuously volatilized mercury even after 10 days without loss of activity. Received: 21 February 2001 / Accepted: 13 March 2001     

Top-down control on plankton components in an Antarctic pond: experimental approach to the study of low-complexity food webs

In order to address the top-down effect on the different phytoplankton size-fractions and ciliates, a survey at microcosm scale was conducted in a hypertrophic Antarctic pond, testing the hypotheses that (1) the picophytoplankton is regulated by a top-down control exerted by organisms of the bigger size-fractions, and (2) the nanoplankton fraction (algae and ciliates) is not regulated by a top-down control exerted by the microplankton. The treatments enclosed pond water that was filtered to obtain the different plankton sizes: (a) through 55 μm, (b) 20 μm, and (c) 3 μm pore size filters. The variation in the net growth rate (k′) of the phytoplankton size-fractions and ciliates was analysed after 4 days. The results determined a significant difference (P<0.011) in the k′ value of the picophytoplankton when nano and micro-sized fractions where removed. Conversely, nanophytoplankton and nanociliates were not affected by the removal of bigger size-fractions. We suggest that in this pond the top-down control of the picophytoplankton is relevant, and that the grazing impact is not a key factor in the regulation of the nano-sized (algae and ciliates) plankton components.     

Measurement of particle diameter of <Emphasis Type="Italic">Lactobacillus acidophilus</Emphasis> microcapsule by spray drying and analysis on its microstructure

Lactobacillus acidophilus, as a probiotic, is widely used in many functional food products. Microencapsulation not only increases the survival rate of L. acidophilus during storage and extends the shelf-life of its products, but also optimal size microcapsule makes L. acidophilus have an excellent dispersability in final products. In this paper, L. acidophilus was microencapsulated using spray drying (inlet air temperature of 170°C; outlet air temperature of 85–90°C). The wall materials used in this study were β-cyclodextrin and acacia gum in the proportion of 9:1 (w/w), and microcapsules were prepared at four levels of wall materials (15, 20, 25 and 30% [w/v]) with a core material concentration of 6% (v/v). The microcapsule diameters were measured by Malvern’s Mastersizer-2000 particle size analyzer. The results showed that the particle diameters of microcapsule were mostly within 6.607 μm and 60.256 μm and varied with 2.884–120.226 μm (the standard smaller microcapsule designated as <350 μm). Through comparison of microcapsule size and uniformity with different concentration of wall materials, we concluded that the optimal concentration of wall material was 20% (w/v), which gave microcapsule with a relatively uniform size (averaging 22.153 μm), and the number of surviving encapsulated L. acidophilus was 1.50 × 10⁹ c.f.u./ml. After 8 weeks storage at 4°C, the live bacterial number was above 10⁷ c.f.u./ml, compared with unencapsulated L. acidophilus, 10⁴–10⁵ c.f.u./ml. Through the observation of scanning electron microscopy, we found that the shapes of microcapsule were round and oval, and L. acidophilus cells located in the centre of microcapsule.     

Chla-specific productivity of picophytoplankton not higher than that of larger phytoplankton off the South Shetland Islands in summer

Size-fractionated chlorophyll a (Chla)-specific productivity (μgC μgChla ⁻¹ h⁻¹) was measured at 11 stations off the northern coast of the South Shetland Islands during summer. The Chla-specific productivity of the 2- to 10 or 10- to 330-μm fraction was highest at 100% and 23% light depths. The Chla-specific productivity of the 2- to 10-μm fraction was generally highest, and that of the <2 or 10- to 330-μm fraction was sometimes highest at 12% and 1% light depths. Temperature was less than 3°C within the euphotic zone at all stations. The hypothesis of Shiomoto et al., according to which Chla-specific productivity of picophytoplankton (<2 μm) is not significantly higher than that of larger phytoplankton (>2 μm) in water colder than 10°C, was supported on condition that light is not limited for larger phytoplankton. Received: 16 September 1997 / Accepted: 8 December 1997     

Fine structure of acrosome biogenesis and of mature sperm in the bivalve molluscs<Emphasis Type="Italic"> Glycymeris</Emphasis> sp. (Pteriomorphia) and<Emphasis Type="Italic"> Eurhomalea rufa</Emphasis> (Heterodonta)

Proacrosomal vesicles form during the pachytene stage, being synthetized by the Golgi complex in Glycymeris sp., and by both the Golgi and the rough endoplasmic reticulum in Eurhomalea rufa. During early spermiogenesis, a single acrosomal vesicle forms and its apex becomes linked to the plasma membrane while it migrates. In Glycymeris sp., the acrosomal vesicle then turns cap-shaped (1.8 μm) and acquires a complex substructure. In E. rufa, proacrosomal vesicles differentiate their contents while still at the premeiotic stage; as the acrosomal vesicle matures and its contents further differentiate, it elongates and becomes longer than the nucleus (3.2 μm), while the subacrosomal space develops a perforatorium. Before condensation, chromatin turns fibrillar in Glycymeris sp., whereas it acquires a cordonal pattern in E. rufa. Accordingly, the sperm nucleus of Glycymeris sp. is conical and elongated (8.3 μm), and that of E. rufa is short and ovoid (1.1 μm). In the midpiece (Glycymeris sp.: 1.1 μm; E. rufa: 0.8 μm), both species have four mitochondria encircling two linked orthogonal (Glycymeris sp.) or orthogonal and tilted (30–40°; E. rufa) centrioles. In comparison with other Arcoida species, sperm of Glycymeris sp. appear distinct due to the presence of an elongated nucleus, a highly differentiated acrosome, and four instead of five mitochondria. The same occurs with E. rufa regarding other Veneracea species, with the acrosome of the mature sperm strongly resembling that of the recent Mytilinae. Electronic Publication     

Vancomycin-resistance Transferability from VanA Enterococci to <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

In last decade methicillin-resistant Staphylococcus aureus with high level of vancomycin-resistance (VRSA) have been reported and generally the patients with VRSA infection were also infected with a vancomycin-resistant Enterococcus (VRE). Considering that the high level of vancomycin-resistance in VRSA isolates seems to involve the horizontal transfer of Tn1546 transposon containing vanA gene from coinfecting VRE strains, the authors have studied the “in vitro” conjugative transfer of this resistance from VanA enterococci to S. aureus. Out of 25 matings performed combining five vancomycin-resistant enterococci as donors (three Enterococcus faecalis and two Enterococcus faecium), and five S. aureus as recipients, all clinical isolates, two have been successful using E. faecalis as donor. The transfer of vancomycin-resistance was confirmed by vanA gene amplification in both transconjugants and the resistance was expressed at lower levels (MIC 32 μg/ml) in comparison with the respective VRE donors (MIC > 128 μg/ml). The vancomycin-resistance of trasconjugants was maintained even after subsequent overnight passages on MSA plates containing subinhibitory levels of vancomycin. This study shows that the vanA gene transfer can be achieved through techniques “in vitro” without the use of laboratory animals employed, in the only similar experiment previously carried out by other authors, as substrate for the trasconjugant growth. Moreover, in that previous experiment, contrary to this study, the vancomycin resistant S. aureus trasconjugants were selected on erythromycin agar and not by direct vancomycin agar selection.     

Decomposition ‘hotspots’ in a rewetted peatland: implications for water quality and carbon cycling

The hypothesis that specific components of seawater, such as particulate, dissolved and colloidal organic and inorganic material, render virions non-infective has long been postulated, but never rigorously tested. To address this hypothesis, the plaque assay method was used to derive infective decay rates, k, of two bacteriophages—P1 (marine host: PWH3a) and T4 (enteric host: E. coli B). We compared k values of bacteriophage suspended in serial filtrations of seawater, with and without autoclaving and UV oxidation. Both phages exhibited reduced decay rates in particle-free water (<0.2 μm) compared to <10 μm filtrate. The largest decrease in virion decay rates was achieved by autoclaving the 0.2 μm filtrate. UV oxidation of <0.2 μm filtrate, however, yielded higher decay rates than observed in autoclaved treatments. The lowest k values were seen in ultra-filtered seawater (<10 kDa). Exposure to a wide range of concentrations of Pronase E (a proteolytic enzyme), inorganic clay (kaolinite or montmorillonite), and organic particles (phytoplankton debris) did not promote phage inactivation. P1 infective titers were also not consistently reduced by exposures to axenic cultures of a resistant host mutant (PWH3a-R) and a non-host marine bacterium (MB-5). Finally, phage were exposed to a range of temperatures to derive activation energies required for phage inactivation. Application of the Arrhenius model to inactivation of T4 and P1 yielded activation energies (E _a) of 49 and 40 kJ mol⁻¹, respectively. This is the first comprehensive analysis in which specific seawater components were assayed for their ability to inactivate bacteriophage. Inactivation of these phage does not appear to depend on capsomere denaturation, proteolytic extracellular enzymes, sorption to non-host bacteria, clay particles or particulate organic debris, but is accelerated by naturally occurring particles, which include living organisms, and heat-labile colloids and macromolecules >10 kDa.     

Recent Fluctuations in Distribution and Biomass of Cold and Warm Temperature Species of Laminarialean Algae at Cape Ohma, Northern Honshu, Japan

The Cape Ohma region of Shimokita Peninsula, the northernmost point of Honshu Island, Japan, is subject to both the warm Tsugaru Current and the cold Kurile Current. As a result, the Laminarialean flora includes both cold temperature species (Laminaria japonica Areschoug, Kjellmaniella crassifolia Miyabe and Costaria costata (C. Agardh) Saunders) and warm temperature species (Undaria peterseniana (Kjellman) Okamura, Ecklonia stolonifera Okamura), as well as Undaria pinnatifida (Yendo) Okamura, which is distributed in both waters. The frequency of occurrence (as a measure of distribution) and the biomass of these species were recorded in June 1976 (at 50 points in depths between 8–30 m), July 1988 (192 points, 2.5–25 m) and July 2001 (78 points, 2.5–25 m). Comparison of these data revealed a decrease in cold temperature species and an increase in warm temperature species from 1976 or 1988 to 2001. Long-term data of seawater temperature measured at 5 m depth near the study site showed that mean temperatures in the middle of winter (late January to February) in 1989–2000 were 0.9–1.1 ^∘C higher than those in 1980–1988. Higher seawater temperatures in the last decade appear to have affected the frequency of occurrence and biomass of the Laminarialean species along the coasts of Cape Ohma. This result supported our previous conclusion that 1 ^∘C higher mean seawater temperature in late January caused a decrease in the biomass of L. japonica (by ca. 64%) along the same coast.     

Growth rate of <Emphasis Type="Italic">Daphnia</Emphasis> feeding on seston in a Siberian reservoir: the role of essential fatty acid

Specific growth rates (based on biomass increment in unit time) of Daphnia fed natural reservoir seston from a eutrophic Siberian reservoir were studied during four vegetation seasons in a laboratory flow-through system. Concentrations of particulate C, N, and P in reservoir seston <115 μm were comparatively high, 1.9, 0.2, and 0.05 mg l⁻¹, respectively; maximum C:P ratio was 259 mol:mol. According to conventional thresholds, concentrations of elements and their stoichiometry did not limit the growth rate of Daphnia. Eicosapentaenoic acid (EPA) in seston significantly effected the growth rates at concentrations up to ∼13 μg l⁻¹ (regression ANOVAR F-test value was 7.91), but not above this concentration. Thus, we consider this concentration of EPA in seston <115 μm to be the limiting concentration of EPA for the growth of Daphnia (longispina group), i.e., below this concentration EPA was the best single predictor of the growth of Daphnia.     

Domoic acid neurotoxicity in hippocampal slice cultures

Summary.  The neurotoxicity of domoic acid was studied in 2–3 week old rat hippocampal slice cultures, derived from 7 day old rat pups. Domoic acid 0.1–100 μM was added to the culture medium for 48 hrs, alone or together with the glutamate receptor antagonists NS-102 (5-Nitro-6,7,8,9-tetrahydrobenzo[G]indole-2,3-dione-3-oxime), NBQX (2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline) or MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine hydrogen maleate), followed by transfer of the cultures to normal medium for additional 48 hrs. Neuronal degeneration in the fascia dentata (FD), CA3 and CA1 hippocampal subfields was monitored and EC₅₀ values estimated by densitometric measurements of the cellular uptake of propidium iodide (PI). The CA1 region was most sensitive to domoic acid, with an EC₅₀ value of 6 μM domoic acid, estimated from the PI-uptake at 72 hrs. Protective effects of 10 μM NBQX against 3 and 10 μM domoic acid were observed for both dentate granule cells and CA1 and CA3c pyramidal cells. NS102 and MK 801 only displayed protective effects when combined with NBQX. MK801 significantly increased the combined neuroprotective effect of NBQX and NS102 against 10 μM domoic acid in both CA1 and FD, but not in CA3. We conclude, that domoic acid neurotoxicity in CA3 and in hippocampal slice cultures in general primarily involves AMPA/kainate receptors. At high concentrations (10 μM domic acid) NMDA receptors are, however, also involved in the toxicity in CA1 and FD. Received June 29, 2001 Accepted August 6, 2001 Published online June 3, 2002