VEGETATIVE REPRODUCTION AND SEXUAL LIFE CYCLE OF THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM FROM TASMANIA,AUSTRALIA1

The toxic, chain-forming dinoflagellate Gymnodinium catenatum Graham was cultured from vegetative cells and benthic resting cysts isolated from estuarine waters in Tasmania, Australia. Rapidly dividing, log phase cultures formed long chains of up to 64 cells whereas stationary phase cultures were composed primarily of single cells (23-41 pm long, 27-36 pm wide). Vegetative growth (mean doubling time 3-4 days) was optimal at temperatures from 14.5-20° C, salinities of 23-34% and light irradiances of 50-300 μE·m^?2·s^?1. The sexual life cycle of G. catenatum was easily induced in a nutrient-deficient medium, provided compatible opposite mating types were combined (heterothallism). Gamete fusion produced a large (59-73 μm long, 50-59 μm wide) biconical, posteriorly biflagellate planozygote (double longitudinal flagellum) which after several days lost one longitudinal flagellum and gradually became subspherical in shape. This older planozygote stage persisted for up to two weeks before encysting into a round, brown resting cyst (42-52 μm diam; hypnozygote) with microreticulate surface ornamentation. Resting cysts germinated after a dormancy period as short as two weeks under our culture conditions, resulting in a single, posteriorly biflagellate germling cell (planomeiocyte). This divided to form a chain of two cells, which subsequently re-established a vegetative population. Implications for the bloom dynamics of this toxic dinoflagellate, a causative organism of paralytic shellfish poisoning, are discussed.     

THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM (DINOPHYCEAE) REQUIRES MARINE BACTERIA FOR GROWTH1

Interactions with the bacterial community are increasingly considered to have a significant influence on marine phytoplankton populations. Here we used a simplified dinoflagellate‐bacterium experimental culture model to conclusively demonstrate that the toxic dinoflagellate Gymnodinium catenatum H. W. Graham requires growth‐stimulatory marine bacteria for postgermination survival and growth, from the point of resting cyst germination through to vegetative growth at bloom concentrations (10³ cells · mL^?1). Cysts of G. catenatum were germinated and grown in unibacterial coculture with antibiotic‐resistant or antibiotic‐sensitive Marinobacter sp. DG879 or Brachybacterium sp., and with mixtures of these two bacteria. Addition of antibiotics to cultures grown with antibiotic‐sensitive strains of bacteria resulted in death of the dinoflagellate culture, whereas cultures grown with antibiotic‐resistant bacteria survived antibiotic addition and continued to grow beyond the 21 d experiment. Removal of either bacterial type from mixed‐bacterial dinoflagellate cultures (using an antibiotic) resulted in cessation of dinoflagellate growth until bacterial concentration recovered to preaddition concentrations, suggesting that the bacterial growth factors are used for dinoflagellate growth or are labile. Examination of published reports of axenic dinoflagellate culture indicate that a requirement for bacteria is not universal among dinoflagellates, but rather that species may vary in their relative reliance on, and relationship with, the bacterial community. The experimental model approach described here solves a number of inherent and logical problems plaguing studies of algal‐bacterium interactions and provides a flexible and tractable tool that can be extended to examine bacterial interactions with other phytoplankton species.     

THE UNIQUE,MICRORETICULATE CYST OF THE NAKED DINOFLAGELLATE GYMNODINIUM CATENATUM1

Gymnodinium catenatum Graham is an unarmored dinoflagellate responsible for episodes of paralytic shellfish poisoning. This species forms a resting cyst that is unique in several ways. The outer surface of the spherical, brownish cyst is microreticulate and composed of hundreds of 1-3 μm polygons. In several regions, these polygons are smaller, more uniform in shape, and oriented in distinct bands that define morphological features. These features on the cyst reflect the cingulum, sulcus, flagellar pore complex, and acrobase of the motile stage precursor to the cyst. The archeopyle is irregularly but extensively developed. Its margin is generally smooth and extends almost completely around the circumference of the cyst, though not consistently in the plane of the equator. The cyst wall is resistant to acetolysis and standard palynological preparation techniques. Gymnodinium catenatum Graham is emended to include the details of the cyst stage. The significance of this cyst is that it is the first described cyst of a naked dinoflagellate that bears oriented surface ornamentation reflecting features of the motile dinoflagellate. Its microreticulate surface ornamentation is unique to dinocysts, naked or armored, living or fossilized. Resistance of the cyst wall to harsh processing techniques suggests the presence of sporopollenin-like material commonly associated with cysts of armored dinoflagellates. From an ecological standpoint, the existence of a G. catenatum cyst has important implications with respect to species bloom dynamics and geographic distribution. In addition, the distinct differences between this cyst and those of the armored saxitoxin-producing gonyaulacoid species argues against a proposed evolutionary linkage.     

GENETIC VARIATION AMONG STRAINS OF THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM (DINOPHYCEAE)

The toxic dinoflagellate Gymnodinium catenatum Graham has formed recurrent toxic blooms in southeastern Tasmanian waters since its discovery in the area in 1986. Current evidence suggests that this species might have been introduced to Tasmania prior to 1973, possibly in cargo vessel ballast water carried from populations in Japan or Spain, followed by recent dispersal to mainland Australia. To examine this hypothesis, cultured strains from G. catenatum populations in Australia, Spain, Portugal, and Japan were examined using allozymes and randomly amplified polymorphic DNA (RAPD). Allozyme screening detected very limited polymorphism and was not useful for population comparisons; however, Australian, Spanish, Portuguese, and Japanese strains showed considerable RAPD diversity, and all strains examined represented unique genotypes. Multidimensional scaling analysis (MDS) of RAPD genetic distances between strains showed clear separation of strains into three nonoverlapping regional clusters: Australia, Japan, and Spain/Portugal. Analysis of genetic distances between strains from the three regional populations indicated that Australian strains were almost equally related to both the Spanish/Portuguese population and the Japanese population. Analysis of molecular variance (AMOVA) found that genetic variation was partitioned mainly within populations (87%) compared to the variation between the regions (8%) and between populations within regions (5%). The potential source population for Tasmania’s introduced G. catenatum remains equivocal; however, strains from the recently discovered mainland Australian population (Port Lincoln, South Australia, 1996) clustered with Tasmanian strains, supporting the notion of a secondary relocation of Tasmanian G. catenatum populations to the mainland via a shipping vector. Geographic and temporal clustering of strains was evident among the Tasmanian strains, indicating that genetic exchange between neighboring estuaries is limited and that Tasmanian G. catenatum blooms are composed of localized, estuary-bound subpopulations.     

PURIFICATION AND CHARACTERIZATION OF A SULFOTRANSFERASE SPECIFIC TO N-21 OF SAXITOXIN AND GONYAUTOXIN 2+3 FROM THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM (DINOPHYCEAE)

A sulfotransferase (ST) specific to N-21 of saxitoxin (STX) and gonyautoxin 2+3 (GTX2+3) designated as N-ST was purified to homogeneity from the cytosolic fraction of clonal-axenic vegetative cells of the toxic dinoflagellate Gymnodinium catenatum Graham GC21V, which causes paralytic shellfish poisoning. The enzyme transferred a sulfate group from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to N-21 in the carbamoyl group of STX and GTX2+3 to produce GTX5 and C1+2, respectively. The molecular mass of the purified enzyme was determined by SDS-PAGE to be 59 kDa. Gel filtration chromatography showed a native molecular mass of 65 kDa, indicating that the N-ST is a monomeric enzyme. The N-ST was specific to only N-21 of STX and GTX2+3, and O-22 sulfation was not observed. Moreover, the N-ST was not active toward neo STX and GTX1+4, which differed from STX and GTX2+3, respectively, in only N-1 hydroxylation. When various compounds previously reported to be substrates for STs in other organisms and paralytic shellfish poisoning toxins other than STX and GTX2+3 were added to the reaction mixture, N-ST activity was not decreased. The enzyme required PAPS as the sole source of sulfate. The enzyme was optimally active at pH 6.0 and 25° C, and its activity was enhanced by Mg^{2 +} and Co^{2 +} . The K_m values of the N-ST for STX and GTX2+3 were 16.1 μM and 29.8 μM, respectively.     

EFFECTS OF TURBULENCE ON THE MARINE DINOFLAGELLATE GYMNODINIUM NELSONII1

Laboratory experiments were conducted to study the effects of agitation on growth, cell division, and nucleic acid dynamics of the dinoflagellate Gymnodinium nelsonii Martin. When cultures were placed on an orbital shaker at 100 rpm, cell division was prevented, cellular volume increased up to 1.5 times that of the nonperturbed cells, the form and location of the cell nucleus were modified, and the RNA and DNA concentrations per cell increased up to 10 times those of the controls. When shaking was stopped after 10 days, cells divided immediately at about 2/3 of the division rate of the unshaken populations, and all the altered parameters were restored. If the agitation continued for more than 20 days, total cell death and disintegration occurred. Several cellular types differing in size and shape were observed in the control and shaken cultures. One possible hypothesis for these results is that failure of the cell to divide results from physical disturbance of the microtubule assemblage associated with chromosome separation during mitosis. My study suggests that small-scale oceanic turbulence of sufficient intensity may inhibit growth of individual dinoflagellate cells, but immediate development of the population may continue when calm weather follows the active mixing period.     

SHORT-TIME SCALE DEVELOPMENT OF A GYMNODINIUM CATENATUM POPULATION IN THE RIA DE VIGO (NW SPAIN)1

Wind direction and fresh water runoff determine the circulation pattern of the Ría de Vigo (NW Spain), which in turn influence the selection and distribution of its phytoplankton populations. Coastal winds with a south–southwesterly component reverse the positive estuarine circulation in the Ría, causing an off-shore to in-shore flow of surface waters and, consequently, the outflow of inner waters via deeper layers. We found that this reversal imposed a selective force on the phytoplankton population: diatoms, which could not counteract the sinking movement of the surface waters, were diminished, while dinoflagellates remained in the water column. From the end of September to the beginning of October 1993, an accumulation of Gymnodimium catenatum Graham was observed coinciding with an intrusion of coastal water induced by westerly winds which provoked a reversal in the circulation of the Ría. The slow reestablishment of the positive estuarine circulation pattern, which was due to a weak coastal upwelling and considerable fresh water runoff, allowed the population of G. catenatum to flourish.     

NUCLEAR FEATURES AND EFFECT OF NUTRIENTS ON GYMNODINIUM CATENATUM (DINOPHYCEAE) SEXUAL STAGES1

Gymnodinium catenatum Graham is an unarmored, cyst‐forming dinoflagellate species responsible for outbreaks of paralytic shellfish poisoning. The nuclear development of the cells during the sexual cycle and the effect of different nitrate and phosphate external levels on sexual stages were studied. Nuclear fusion of gametes occurred before or at the same time as cytoplasmic fusion. During this process, either both nuclei migrated to a central area in the sulcal region, or only one of them migrated to the other nucleus. The motile and longitudinally biflagellated zygote presented a large, pear‐shaped nucleus, and either divided or encysted. Planozygotes and germlings underwent similar division processes, which suggested an uncoordinated meiosis in both encysting and non‐encysting zygotes. Encystment in culture was greater under low nitrate and phosphate limitation (L/15) than when only one or neither of these nutrients were added (L‐N, L‐P, and ‐N‐P). However, planozygotes individually monitored achieved the maximum encystment (40%) in a medium with no phosphate or nitrate added (‐N‐P), while most of them divided (70%–90%) in replete (L1) or half‐replete (L‐N and L‐P) media. Low levels of nitrate in the medium of cyst formation promoted a deficient development of the cyst wall. On the other hand, low phosphate levels in the medium of germination prevented both planozygote and germling division and lowered the final germination frequencies of cysts. The minimum dormancy, with an average value of 13.7±5.5 days, was not affected by any of the nutritional conditions studied.     

A SURVEY OF THE STEROL COMPOSITION OF THE MARINE DINOFLAGELLATES KARENIA BREVIS,KARENIA MIKIMOTOI,AND KARLODINIUM MICRUM: DISTRIBUTION OF STEROLS WITHIN OTHER MEMBERS OF THE CLASS DINOPHYCEAE1

The sterol composition of different marine microalgae has been examined to determine the utility of sterols as biomarkers to distinguish members of various algal classes. For example, members of the class Dinophyceae possess certain 4‐methyl sterols, such as dinosterol, which are rarely found in other classes of algae. The ability to use sterol biomarkers to distinguish certain dinoflagellates such as the toxic species Karenia brevis Hansen and Moestrup, responsible for red tide events in the Gulf of Mexico, from other species within the same class would be of considerable scientific and economic value. Karenia brevis has been shown by others to possess two major sterols, (24S)‐4α‐methyl‐5α‐ergosta‐8(14),22‐dien‐3β‐ol (ED) and its 27‐nor derivative (NED), having novel structures not previously known to be present in other dinoflagellates. This prompted the present study of the sterol signatures of more than 40 dinoflagellates. In this survey, sterols with the properties of ED and NED were found in cultures of K. brevis and shown also to be the principal sterols of Karenia mikimotoi Hansen and Moestrup and Karlodinium micrum Larsen, two dinoflagellates closely related to K. brevis. They are also found as minor components of the more complex sterol profiles of other members of the Gymnodinium/Peridinium/Prorocentrum (GPP) taxonomic group. The distribution of these sterols is consistent with the known close relationship between K. brevis, K. mikimotoi, and K. micrum and serves to limit the use of these sterols as lipid biomarkers to a few related species of dinoflagellates.     

THE FATTY ACID AND STEROL COMPOSITION OF FIVE MARINE DINOFLAGELLATES

The fatty acid and sterol compositions of five species of marine dinoflagellates (Scrippsiella sp. Symbiodinium microadriaticum Freud, Gymnodinium sp., Gymnodinium sanguineum Hirasaki, and Fragilidium sp.) are reported. All contained the major fatty acids that are considered common in dinoflagellates, but the proportions were quite variable, and some species contained low contents of some polyunsaturated fatty acids. Concentration ranges for the major fatty acids were: 16:0 (9.0%–24.8%), 18:4(n-3) (2.5%–11.5%), 18:5(n-3) (7.0%–43.1%), 20:5(n-3) (EPA) (1.8%–20.9%), and 22:6(n-3) (DHA) (9.9%– 26.3%). Small amounts of novel very-long-chain highly unsaturated C₂₈ fatty acids occurred in all species. Each dinoflagellate contained a complex mixture of 4-methyl sterols and 4-desmethyl sterols. Four species contained cholesterol, although the amounts were highly variable (from 0.2% of total sterols in Scrippsiella sp. to 45.6% in Fragilidium sp.). All but G. sanguineum contained the 4-methyl sterol dinosterol, and all species contained sterols lacking a double bond in the ring system (i.e. stanols); in Scrippsiella sp. cholestanol composed 24.3% of the total sterols. Other common features of the 4-methylsterol profiles were the presence of 23,24-dimethyl alkylation and unsaturation at Δ²² in the side chain. In Scrippsiella sp., four steroidal ketones were identified: cholestanone, dinosterone, 4α,23,24-trimethyl-5α-cholest-8(14)-en-3-one, and dinostanone. The structures of these corresponded to the major sterols in this species, suggesting that the sterols and steroidal ketones are biosynthetically linked. Steroidal ketones were not detected in the other species. Although fatty acid profiles can be used to distinguish among algal classes, they were not useful for differentiating among dinoflagellate species. In contrast, whereas some taxonomic groupings of dinoflagellates display similar sterol patterns, others, such as the gymnodinoids studied here, clearly do not. The combination of fatty acid, sterol, and steroidal ketone profiles may be useful complementary chemotaxonomic tools for distinguishing morphologically similar species. The identification of steroidal ketones supports earlier suggestions that certain dinoflagellates might be a significant source of such components in marine environments.     

PHAGOTROPHIC FEEDING AND ITS IMPORTANCE TO THE LIFE CYCLE OF THE HOLOZOIC DINOFLAGELLATE,GYMNODINIUM FUNGIFORME1

The holozoic dinoflagellate, Gymnodinium fungiforme Anissimova, has been observed in both asexually and sexually reproducing cultures. Asexual reproduction is characterized by zoosporangium formation and subsequent new cell release. Sexuality is gametic, and planozygotes and hypnozygotes are present. The life cycle is highly dependent on feeding, and in food-depleted cultures the swimming cells rapidly disappear. These are replaced with resistant long-term resting cysts. Despite its small size (8.5–19 μm), G. fungiforme can feed on prey as large as the ciliated protozoan, Condylostoma magnum Spiegel (600–1000 μm in length), or small injured metazoans, and has been cultured phagotrophically with the chlorophyte, Dunaliella salina Teodoresco as a food source. Eleven additional species of algae including 1 chlorophyte, 7 chrysophytes and 3 rhodophytes, however, were not suitable as food sources. Feeding is characterized by the formation of ‘dynamic aggregations’ of hundreds of dinoflagellates that attach to the surface of a prey organism by a peduncle. G. fungiforme ingests the cytoplasm or body fluids of its prey and a feeding aggregation can ingest a C. magnum in 20–30 minutes.     

MODULATION OF FATTY ACIDS IN THE MEMBRANES OF ANACYSTIS NIDULANS (CYANOBACTERIA): INCORPORATION OF ODD-NUMBERED CARBON FATTY ACIDS1

Anacystis nidulans Richt., a unicellular cyanobacterium, can incorporate exogenously supplied fatty acids, including odd-numbered carbon fatty acid (OFAs), into the acylglycerols of cell membranes. Data are presented for the uptake of undecanoic acid (11:0) into cells of A. nidulans, the subsequent elongation up to C17, and incorporation of OFA into the four major membrane acylglycerols. The incorporation of OFAs was followed by desaturation of part of the saturated fatty acid to monoenoic fatty acid. Positional analyses of the double bonds of these manoenoic fatty acids suggest that there is one desaturase that inserts a Δ⁹ bond in both odd- and even-numbered fatty acids of varying chain length. Our data also suggest that there is no positional specificity for chain length on the glycerol backbone by the acyltransferases.     

VARIATIONS OF PSP TOXIN PROFILES DURING DIFFERENT GROWTH PHASES IN GYMNODINIUM CATENATUM (DINOPHYCEAE) STRAINS ISOLATED FROM THREE LOCATIONS IN THE GULF OF CALIFORNIA,MEXICO1

In vitro experiments were performed with Gymnodinium catenatum Graham strains isolated from three locations in the Gulf of California to determine the variability in toxicity and toxin profiles. Strains were cultivated in GSe at 20°C±1°C, 150 μmol photons·m^?2·s^?1 (12:12 light:dark cycle), and harvested during different growth phases. Growth rates were higher than in previous studies, varying between 0.70 and 0.82 day^?1. The highest cell yields were reached at 16 and 19 days, with maximum densities between 1090 and 3393 cells·mL^?1. Bahía de La Paz (BAPAZ) and Bahía de Mazatlán (BAMAZ) were the most toxic (101 pg STXeq·cell^?1), whereas strains from Bahía Concepción (BACO) were the least toxic (13 pg STXeq·cell^?1). A strain isolated from cyst germination was one of the least toxic strains. No significant changes in toxin content with culture age were observed (0.2 and 0.6 pmol paralytic shellfish poisoning·cell^?1). All strains contained neosaxitoxin (NEOSTX), decarbamoyl‐saxitoxin (dcSTX), decarbamoyl‐gonyautoxin‐2,‐3, (dcGTX2‐3), N‐sulfo‐carbamoylsaxitoxin (B1), N‐sulfo‐carbamoylneosaxitoxin (B2), and N‐sulfo‐carbamoylgonyautoxin‐2,‐3 (C1‐2). Bahía Concepción strains had the highest content of C1; BAPAZ and BAMAZ strains had a higher percentage of NEOSTX. Differences in toxin composition with culture age were observed only in BAMAZ and BAPAZ strains. Cultures with a higher percentage of long chains had more NEOSTX, while those with a higher proportion of short chains had a lower content of NEOSTX. Gulf of California strains are characterized by a high proportion of NEOSTX, and seem to have evolved particular physiological responses to their environment that are reflected in the toxin profile, suggesting different populations.     

MORPHOSPECIES VS. GENOSPECIES IN TOXIC MARINE DINOFLAGELLATES: AN ANALYSIS OF GYMNODZNIUM CATENATUM/GYRODINIUM IMPUDICUM AND ALEXANDRIUM MINUTUM/A. LUSITANICUM USING ANTIBODIES,LECTINS, AND GENE SEQUENCES1

Morphological features are the predominant criteria used to define species of marine dinoflagellates. Taxonomic problems with some toxic groups has led to the implementation of molecular taxonomy techniques and development of a genospecies concept. As a result, the relationships between “morphospecies” and “genospecies” has been questioned. In this study, the genetic differentiation between two sets of closely related morphospecies, Gymnodinium catenatum Graham/Gyrodinium impudicum Fraga and Alexandrium minutum Halim/Alexandrium lusitanicum Balech, were analyzed. The extent of morphological differentiation existing within these two groups is of the same order of magnitude. Analysis of cell surface antigens detected by preadsorbed serum, cell surface glycan moieties detected by lectins and sequencing of the D9 and D10 domains of the Large-subunit ribosomal RNA gene, showed that the extent of genetic differentiation existing between the dinofagellates Gymnodinium catenatum/Gyrodinium impudicum is substantial. Therefore, both morphological and genetic criteria resolve these organisms as two distinct entities. In contrast, Alexandrium minutum/Alexandrium lusitanicum were indistinguishable using the some suite of molecular markers. The findings demonstrated that classifications based on morphological criteria may be incongruous. On a practical level, molecular taxonomy provides useful tools to distinguish between morphologically similar microalgal species and furthermore can prevent misidentification of species such as Gymnodinium catenatum/Gyrodinium impudicum, a frequent occurrence when samples are fixed with Lugol's or formaldehyde solution.     

FATTY ACIDS,AMINO ACIDS,MINERAL CONTENTS,AND PROXIMATE COMPOSITION OF SOME BROWN SEAWEEDS1

This study was conducted to create a nutritional database on brown seaweeds and to popularize their consumption and utilization in Iran. The fatty acid contents, amino acids profiles, and certain mineral elements composition of some brown seaweeds, Padina pavonica (L.) Thivy, Dictyota dichotoma (Huds.) J. V. Lamour., and Colpomenia sinuosa (Mert. ex Roth) Derbés et Solier were determined. Total lipid content ranged from 1.46 ± 0.38 to 2.94 ± 0.94 g · 100 g^?1dry weight (dwt), and the most abundant fatty acids were C16:0, C18:1, C20:4 ω6, and C20:5 ω3. The unsaturated fatty acids predominated in all species and had balanced sources of ω3 and ω6 acids. Highest total polyunsaturated fatty acid (PUFA) levels occurred in C. sinuosa. The protein content of D. dichotoma was 17.73 ± 0.29 g · 100 g^?1dwt, significantly higher than the other seaweeds examined. Among amino acids essential to human nutrition, methionine (Met; in D. dichotoma and P. pavonica) and lysine (Lys; in C. sinuosa) were present in high concentrations. The crude fiber content varied by 9.5 ± 11.6 g · 100 g^?1dwt in all species. Chemical analysis indicated that ash content was between 27.02 ± 0.6 and 39.28 ± 0.7 g · 100 g^?1dwt, and that these seaweeds contained higher amounts of both macrominerals (7,308–9,160 mg · 100 g^?1dwt; Na, K, Ca) and trace elements (263–1,594 mg · 100 g^?1dwt; Fe, Ni, Mn, Cu, Co) than have been reported for edible land plants. C. sinuosa had the highest amount of Ca, Fe, and a considerable content of Na was measured in P. pavonica.     

FATTY ACID AND LIPID COMPOSITION OF THE ACIDOPHILIC GREEN ALGA CHLAMYDOMONAS SP.1

The lipid and fatty acid compositions of Chlamydomonas sp. isolated from a volcanic acidic lake and C. reinhardtii were compared, and the effects of pH of the medium on lipid and fatty acid components of Chlamydomonas sp. were studied. The fatty acids in polar lipids from Chlamydomonas sp. were more saturated than those of C. reinhardtii. The relative percentage of triacylglycerol to the total lipid content in Chlamydomonas sp. grown in medium at pH 1 was higher than that in other cells grown at higher pH. A probable explanation might be that Chlamydomonas sp. has two low pH adaptation mechanisms. One mechanism is the saturation of fatty acids in membrane lipids to decrease membrane lipid fluidity, and the other is the accumulation of triacylglycerol, as a storage lipid, to prevent the osmotic imbalance caused by high concentrations of H₂SO₄.     

SYMBIOSIS IN THE PLANKTONIC FORAMINIFER,ORBULINA UNIVERSA,AND THE ISOLATION OF ITS SYMBIOTIC DINOFLAGELLATE,GYMNODINIUM BÉII SP. NOV.1

The symbiotic association of the spinose planktonic foraminifer, Orbulina universa, with the dinoflagellate, Gymnodinium béii sp. nov., was examined with light and electron microscopy, and the symbiont was isolated into unialgal culture. The intact association is characterized by a diurnal movement of the symbionts from the distal regions of the spines during the day, to perialgal vacuoles within the host cytoplasm at night. This diurnal migration involves a daily endo- exocytotic cycle. Gymnodinium béii is non-motile and spindle-shaped within the host, whereas it is motile and gymnodinoid in shape when in culture. Ultrastructural examination revealed two or more stalked pyrenoids penetrated by lamellae, a typical dinokaryon nucleus and no trichocysts. A distinct ‘flange’projects over the sulcus from the hypocone. The swimming behavior of this dinoflagellate was characterized by intermittent darting events. Swimming speeds during a dart reached velocities of 770 μm. s^?1 as compared to a mean, non-darting swimming velocity of 126 μm. s^?1. Gymnodinium béii is eurythermal and division rates ranged between 0.16 and 0.65 divisions day^?1 for culture temperatures between 6.5 and 25° C respectively.     

BIO-OPTICAL CHARACTERISTICS AND PHOTOADAPTIVE RESPONSES IN THE TOXIC AND BLOOM-FORMING DINOFLAGELLATES GYRODINIUM AUREOLUM,GYMNODINIUM GALATHEANUM,AND TWO STRAINS OF PROROCENTRUM MINIMUM1

Photoadaptive responses in the toxic and bloom-forming dinoflagellates Gyrodinium aureolum Hulbert, Gymnodinium galatheanum Braarud, and two strains of Prorocentrum minimum (Pavillard)Schiller were evaluated with respect to pigment composition, light-harvesting characteristics, carbon and nitrogen contents, and growth rates in shade- and light-adapted cells. The two former species were grown at scalar irradiances of 30 and 170 μmol · m ^?2 at a 12-h daylength at 20° C. The two strains of P. minimum were grown at 35 and 500 μmol. m^?2· s^?1 at a 2-h daylength at 20° C. For the first time, chlorophyll (chl) c₃, characteristic of several bloom-forming prymnesiophytes, was detected in G. aureolum and G. galatheanum. Photoadaptional status affected the pigment composition strongly, and the interpretation of the variation depended on whether the pigment composition was normalized per cell, carbon, or chl a. Species-specific and photoadaptional differences in chl a-specific absorption (°a_c, 400–700 nm) and chl a-normalized fluorescence excitation spectra of photosystem II fluorescence with or without addition of DCMU (°F and °F_DCMU 400–700 nm) were evident. Gyrodinium aureolum and G. galatheanum exhibited in vivo spectral characteristics similar to chl c₃-containing prymnesiophytes in accordance with their similar pigmentation. Prorocentrum minimum had in vivo absorption and fluorescence characteristics typical for peridinin-containing dinoflagellates. Species-specific differences in in vivo absorption were also observed as a function of package effect vs. growth irradiance. This effect could be explained by differences in intracellular pigment content, cell size/shape, and chloroplast morphology/numbers. Light- and shade-adapted cells of P. minimum contained 43 and 17% of photoprotective carotenoids (diadino + diatoxanthin) relative to chl a, respectively. The photoprotective function of these carotenoids was clearly observed as a reduction in °F and °F ^DCMU at 400–540 nm compared to °ac in light-adapted cells of P. minimum. Spectrally weighted light absorption (normalized to chl a and carbon, 400–700 nm) varied with species and growth conditions. The use of quantum-corrected and normalized fluorescence excitation spectra with or without DCMU-treated cells to estimate photosynthetically usable light is discussed. The usefulness of in vitro absorption and fluorescence excitation spectra for estimation of the degradation status of chl a and the ratio of chl a to total pigments is also discussed.     

ANTARCTIC DISTRIBUTION,PIGMENT AND LIPID COMPOSITION,AND MOLECULAR IDENTIFICATION OF THE BRINE DINOFLAGELLATE POLARELLA GLACIALIS (DINOPHYCEAE)1

Polarella glacialis (Montresor et al.) was identified in Davis Station sea ice by morphological and DNA sequence comparison of cultures with those of the authentic strain P. glacialis CCMP 1383 isolated from McMurdo Sound. Cells and cysts of the Davis isolate (FL1B) were morphologically indistinguishable from P. glacialis, and comparison of the large subunit rDNA of both cultures demonstrated only 0.2% sequence divergence over 1366 base pairs. The photosynthetic pigments of P. glacialis (strains FL1B and CCMP 1383) were typical of dinoflagellates, with peridinin (contributing up to 31%) as the major accessory pigment. Extremely high levels of polyunsaturated fatty acids (PUFA, up to 76.3%) were characteristic of P. glacialis isolate FL1B. The high PUFA concentration of this species is thought to be an adaptation to survive the cold temperatures of the upper fast ice. The sterol profile of FL1B was atypical of dinoflagellates, with 4‐desmethylsterols (up to 79%) in greater abundance than 4α‐methyl sterols (up to 24%). 27‐Nor‐24‐methylcholest‐5,22E‐dien‐3β‐ol was identified as the principle sterol in P. glacialis, contributing up to 64% of the total sterol composition.