GROWTH AND TOXICITY OF PRYMNESIUM PARVUM (HAPTOPHYTA) AS A FUNCTION OF SALINITY,LIGHT, AND TEMPERATURE1

The growth rate, stationary cell concentration, and toxicity of Prymnesium parvum N. Carter were measured using a strain isolated from Texas inland waters. We used a multifactor experimental approach with multiple regression analysis to determine the importance of environmental factors, including temperature, light, and salinity to these algal measurements. Exponential growth rate was unimodal in relation to temperature, salinity, and irradiance, with an estimated maximal growth of 0.94 d^?1 occurring at 27°C, 22 practical salinity units (psu), and 275 μmol photons·m^?2·s^?1. Stationary cell concentrations also had unimodal responses to temperature and salinity but increased with irradiance. Maximal cell concentrations were estimated to occur at 26°C and 22 psu. Both maximum growth rate and highest stationary cell concentrations were measured at levels of each factor resembling warm, estuarine conditions that differ from the conditions under which blooms occur in inland waters in the southwestern United States. Acute toxicity to fish was highest at the lowest salinity and temperature levels, conditions not optimal for exponential growth but similar to those under which blooms occur in inland waters. Our results imply that summer blooms could occur in inland waters of the southwestern United States. Generally, they have not, suggesting that factors other than those investigated in this research influence bloom dynamics.     

ALLELOPATHY AS AN EMERGENT,EXPLOITABLE PUBLIC GOOD IN THE BLOOM‐FORMING MICROALGA PRYMNESIUM PARVUM

Many microbes cooperatively secrete extracellular products that favorably modify their environment. Consistent with social evolution theory, structured habitats play a role in maintaining these traits in microbial model systems, by localizing the benefits and separating strains that invest in these products from ‘cheater’ strains that benefit without paying the cost. It is thus surprising that many unicellular, well‐mixed microalgal populations invest in extracellular toxins that confer ecological benefits upon the entire population, for example, by eliminating nutrient competitors (allelopathy). Here we test the hypotheses that microalgal exotoxins are (1) exploitable public goods that benefit all cells, regardless of investment, or (2) nonexploitable private goods involved in cell‐level functions. We test these hypotheses with high‐toxicity (TOX+) and low‐toxicity (TOX?) strains of the damaging, mixotrophic microalga Prymnesium parvum and two common competitors: green algae and diatoms. TOX+ actually benefits from dense populations of competing green algae, which can also be prey for P. parvum, yielding a relative fitness advantage over coexisting TOX?. However, with nonprey competitors (diatoms), TOX? increases in frequency over TOX+, despite benefiting from the exclusion of diatoms by TOX+. An evolutionary unstable, ecologically devastating public good may emerge from traits selected at lower levels expressed in novel environments.     

小定鞭藻毒素的分离与鉴定

从大量死鱼的鱼池中收集分离出小定鞭藻Ｐｒｙｍｎｅｓｉｕｍｐｏｒｖｕｍ的毒株,并在实验室成功地进行了单种培养,当温度２３℃,光照６００－８００ｌｘ盐度约１２—１６‰左右时,该藻在海水及人工海水培养基中均生长良好,在对数生长末期到平衡期溶血毒素活性最高。从藻细胞及浓缩的培养液中提取出二种毒素：溶血毒素（Ｈａｅｍｏｌｙｔｉｃｔｏｘｉｎｓ）和鱼毒素（Ｉｃｈｔｈｙｏｔｏｘｉｎｓ）。用新鲜牛血球测定了溶血毒素活性;用孔雀鱼测定了鱼毒素活性。用部分纯化的溶血毒素经元素分析、红外光谱、核磁共振及ＦＡＢ质谱测定,结果显示该藻溶血毒素可能是一个糖脂。     

小三毛金藻对盐碱土池塘毒害鱼类的防治研究

小三毛金藻（PrymnesiumparvumCarter）是一种有害藻类。通过以硫酸盐为主的盐碱土池塘的对照试验,总结出采用不同药物、黄泥土、酸性化肥和追施有机肥、提高池塘肥力、促使其它藻类大量繁殖;同时不定期进行水质分析、加注新水、降低盐度、调节pH值等防治措施,使小三毛金藻得到有效的控制。其防治效率达95％以上。自1985年在陕西省大荔、合阳引用这种防治技术到1997年使万亩盐碱地池塘养鱼水面未受到小三毛金藻大的危害。     

ULTRASTRUCTURE OF PRYMNESIUM NEMAMETHECUM SP. NOV. (PRYMNESIOPHYCEAE)1

Based on material collected from Cape Town, a new sand-dwelling, marine species of Prymnesium is described. Using light and electron microscopy, Prymnesium nemamethecum sp. nov. has been found to resemble other species of the genus in size, organelle arrangement, and swimming behavior. It differs from other described species in that it has three types of scales, one of which is confined to the region of appendage insertion and forms a sheath of simple plate scales over the haptonema. In addition, the scales constituting the proximal body scale layer(s) are unusual because they are not simple plate scales but are specifically ornamented.     

BACTERIAL LYSIS OF AUREOCOCCUS ANOPHAGEFFERENS CCMP 1784 (PELAGOPHYCEAE)1

Water samples from Great South Bay, New York, contained biological agents capable of causing the lysis of the brown‐tide alga Aureococcus anophagefferens Hargraves et Sieburth. From these water samples, 32 bacterial isolates were tested for algicidal effects against the algae. Six of the isolates were shown to have algicidal effects against A. anophagefferens. Sequencing of the gene 16S rRNA revealed that the isolates were relatively diverse. Based on their similarity to sequences in repositories, the isolates seem to be closely related to Bacillus, Halomonas, Croceibacter atlanticus, Marinobacter, and an Arctic deep‐sea bacterium.     

ISOLATION AND CHARACTERIZATION OF A VIRUS THAT INFECTS EMILIANIA HUXLEYI (HAPTOPHYTA)1

The isolation and characterization of a virus (designated EhV) that infects the marine coccolithophorid Emiliania huxleyi (Lohmann) Hay & Mohler are described. Three independent clones of EhV were isolated from Norwegian coastal waters in years 1999 and 2000. EhV is a double‐stranded DNA‐containing virus with a genome size of ～415 kilo‐base pairs. The viral particle is an icosahedron with a diameter of 160–180 nm. The virus particle contains at least nine proteins ranging from 10 to 140 kDa; the major capsid protein weighs ～54 kDa. EhV has a latent period of 12–14 h and a burst size of 400–1000 (mean, 620) viral particles per cell. A phylogenetic tree based on DNA polymerase amino acid sequences indicates EhV should be assigned to the Phycodnaviridae virus family and that the virus is most closely related to viruses that infect Micromonas pusilla and certain Chlorella species.     

DETECTION OF CHLOROPHYLLS c1, c2 AND c3 IN PIGMENT EXTRACTS OF PRYMNESIUM PARWM (PRYMNESIOPHYCEAE)1

Three chlorophyll c-type pigments were separated by reversed-phase high Performance liquid chromatography and thin-layer chromatography from pigment extracts of the prymnesiophyte, Prymnesium parvum Carter. Based on spectral characteristics, retention times, and comparison with reference pigments isolated from the diatom Phaeodactylum tricornutum Bohlin, two of these pigments were identijied as chlorophyll c₁ and c₂. The other pigment was identified by its absorption spectrum and thin-layer chromatography retention times as the newly described chlorophyll c₃. However, in other prymnesiophytes so far examined, chlorophyll c₁ and chlorophyll c₃ were present with no chlorophyll c_l. The discovery of chlorophyll c₃ with chlorophyll c₁ and chlorophyll c₃ in Prymnesium parvum therefore represents the first report of this combination of pigments in prymnesiophytes.     

EFFECT OF SODIUM AND NITRATE ON GROWTH OF ANABAENA FLOS-AQUAE (CYANOPHYTA)1

The growth response of a nitrogen fixing cyanobacterium, Anabaena flos-aquae (Lyng) Bréb., to sodium and nitrate was examined in batch culture under controlled laboratory conditions. Sodium (range 0-12 mg Na⁺· L^-1) enhanced growth of the cyanobacterium under nitrate-sufficient (5.7 mg NO³-N · L^-1) but not nitrate-limited (0.49 mg NO³- N · L^-1) conditions. The magnitude of the growth response was related to the nutritional history of the culture. No significant effect of sodium on nitrate utilization was observed. The increase in ambient sodium levels in many lakes may provide a competitive advantage to cyanobacteria.     

温度对普通小球藻和鱼腥藻生长竞争的影响

通过室内实验研究了不同温度条件下主要水华藻类鱼腥藻(Anabaena sp. strain PCC)和常见淡水藻类普通小球藻(Chlorella vulgaris)的生长和种间竞争, 结果表明在单种培养和共同培养体系中, 普通小球藻的最大藻细胞浓度随着温度的升高而增加; 鱼腥藻生长最适温度为3035℃。温度对藻类种间竞争抑制参数能够产生明显影响, 鱼腥藻在温度为15℃时对普通小球藻的竞争抑制参数最大, 分别是25℃、30℃、35℃时的1.24倍、1.14倍和1.12倍; 而普通小球藻在30℃时对鱼腥藻的竞争抑制参数最大, 分别是15℃、25℃、35℃条件下的4.25倍、2.03倍和1.20倍。在4个试验温度下普通小球藻对鱼腥藻的竞争抑制参数均大于鱼腥藻对普通小球藻的竞争抑制参数。根据Lotka-Volterra竞争模型可推断, 在4个温度条件下, 普通小球藻和鱼腥藻在竞争中不稳定共存。       

ALGICIDAL BACTERIA ACTIVE AGAINST GYMNODINIUM BREVE (DINOPHYCEAE). I. BACTERIAL ISOLATION AND CHARACTERIZATION OF KILLING ACTIVITY1,3

Interactions between bacteria and species of harmful and/or toxic algae are potentially important factors affecting both the population dynamics and the toxicity of these algae. Recent reports of bacteria lethal to certain harmful algal bloom (HAB) species, coupled with a rapidly evolving interest in attempting to minimize the adverse effects of HABs through various prevention, control, and mitigation strategies, have focused attention on defining the role of algicidal bacteria in bloom termination. The aim of the present study was to determine whether algicidal bacteria active against Gymnodinium breve Davis, a dinoflagellate responsible for frequent and protracted red tides in the Gulf of Mexico, are present in the waters of the west Florida shelf. To date, we have isolated two bacterial strains from this region lethal to G. breve and have begun to characterize the algicidal activity of one of these strains, 41-DBG2. This bacterium, a yellow-pigmented, gram-negative rod, was isolated from waters containing no detectable G. breve cells, suggesting that such bacteria are part of the ambient microbial community and are not restricted to areas of high G. breve abundance. Strain 41-DBG2 produced a dissolved algicidal compound(s) that was released into the growth medium, and the algicide was effective against the four Gulf of Mexico G. breve isolates tested as well as a closely related HAB species that also occurs in this region, Gymnodinium mikimotoi Miyake et Kominami ex Oda. Nonetheless, data showing that a nontoxic isolate of Gymnodinium sanguineum Hirasaka from Florida Bay was not affected indicate that the algicidal activity of this bacterium does exhibit a degree of taxonomic specificity. Our efforts are currently being directed at resolving several critical issues, including the identity of the algicide(s), the mechanisms regulating its production and ability to discriminate between target algal species, and how the growth rate of 41-DBG2 is affected by the presence of G. breve cells. We have also proposed a conceptual model for interactions between algicidal bacteria and their target species to serve as a testable framework for ensuing field studies.     

Development of compound microsatellite markers in the harmful red tide species Chattonella ovata (Raphidophyceae)

We isolated 12 polymorphic microsatellites from the noxious red‐tide‐causing alga Chattonella ovata. These loci provide a class of highly variable genetic markers, as the number of alleles ranged from four to 12, and the observed and expected heterozygosities ranged from 0.238 to 0.850 and from 0.310 to 0.889, respectively. These loci are useful for revealing the genetic structure of and gene flow among C. ovata populations.     

RESPONSE OF ANABAENA FLOS-AQUAE (CYANOPHYTA) NITROGENASE ACTIVITY TO SUDDEN PHOSPHATE DEPRIVATION1

Cultures of Anabaena flos-aquae (Lyng.) Breb. Were used to determine changes in nitrogenase activity (acetylene reduction) after external concentrations of phosphorus were lowered. Two days following immersion in phosphorus-free medium, nitrogenase activity (NA) had doubled and required 8 days to return to time zero levels. Subsequent long-term experiments showed that concentrations of soluble reactive phosphorus (SRP) released from the algae transferred into the –P medium reached maximum levels by day 3 and returned to initial low values by days 7–10. NA was always highest during this SRP release-reassimilation phase but steadily decreased after reassimilation was complete. Day 56 NA was 5–14% of initial activity. The data support the hypothesis that heterocyst and vegetative cell ATP pools are discrete and suggest that the short-term effects of phosphorus removal as an aquatic restoration technique need further study.     

BLOOM OF THE GIANT ANADYOMENE GIGANTODICTYON SP. NOV. (ANADYOMENACEAE,CLADOPHORALES) FROM THE OUTER SLOPE (25–50 m) OF THE BELIZE BARRIER REEF1

A giant form of Anadyomene, most similar to Anadyomene pavonina (J. Agardh) Wille, a rare and diminutive alga endemic to Florida, appeared as up to 10 m long net‐like strands covering 10%–80% of a 0.5 km region of the 25–50 m deep Belizean outer reef slope where none had been present up to 12 months earlier. This new species, described herein as Anadyomene gigantodictyon Littler et D. S. Littler, is characterized by a unistratose blade or cluster of blades formed by the polychotomous branching of uniseriate veins, with the interstices, or spaces between the veins, completely or partially filled with cells that are smaller than those of the veins, with cylindrical to ovate cells. The cells at mid‐blade are 1.7–2.0 mm in length and 0.2–0.3 mm diameter; interstitial cells are parallel and not juxtaposed. All cells are joined in one plane and form species‐specific, fan‐shaped patterns with secondary interstitial cells loosely or tightly woven.     

PHOTOTACTIC MOTILITY OF SYNECHOCYSTIS SP. UNIWG (CYANOBACTERIA) FROM BRACKISH ENVIRONMENT1

Although type IV pilus has been implicated in the phototactic motility of some unicellular cyanobacteria, its regulatory mechanism and the effect of environmental factors on motility are still unknown. Equally important is the ability of cyanobacterial cells to anchor themselves to an environment that is conducive for survival. We compared the motility of a newly isolated unicellular brackish cyanobacterium, Synechocystis sp. UNIWG, with the morphologically and phylogenetically similar freshwater cyanobacterium Synechocystis sp. PCC6803 under different environmental conditions. The phototactic motility of Synechocystis sp. UNIWG on semisolid BG‐11 medium with various concentrations of nitrogen source was significantly faster than that of Synechocystis PCC6803. Interestingly, the cell surface of Synechocystis sp. UNIWG showed the presence of rigid spicules when grown in liquid BG‐11, a phenomenon that was absent in Synechocystis PCC6803. Negative staining of Synechocystis sp. UNIWG revealed the presence of two distinct pilus morphotypes, which resembled type IV pili and thin pili of Synechocystis PCC6803. This finding suggested a similar pattern of phototactic motility in both strains. However, the rigid spicules on Synechocystis sp. UNIWG seem to be more of a hindrance during type IV motility. It was determined that the spicules were degraded when the cells moved, such as under prolonged darkness and/or depletion of nitrogen source, indicating that the function of the spicules is to attach the cell to an environment that is conducive for its survival. Thus, Synechocystis sp. UNIWG shows phototaxis regulation that is more complex than Synechocystis PCC6803.     

Feeding by Heterotrophic Dinoflagellates and Ciliates on the Free‐living Dinoflagellate Symbiodinium sp. (Clade E)

To investigate heterotrophic protists grazing on Symbiodinium sp., we tested whether the common heterotrophic dinoflagellates Gyrodinium dominans, Gyrodinium moestrupii, Gyrodinium spirale, Oblea rotundata, Oxyrrhis marina, and Polykrikos kofoidii and the ciliates Balanion sp. and Parastrombidinopsis sp. preyed on the free‐living dinoflagellate Symbiodinium sp. (clade E). We measured the growth and ingestion rates of O. marina and G. dominans on Symbiodinium sp. as a function of prey concentration. Furthermore, we compared the results to those obtained for other algal prey species. In addition, we measured the growth and ingestion rates of other predators at single prey concentrations at which these rates of O. marina and G. dominans were saturated. All predators tested in the present study, except Balanion sp., preyed on Symbiodinium sp. The specific growth rates of O. marina and G. dominans on Symbiodinium sp. increased rapidly with increasing mean prey concentration < ca. 740–815 ng C/ml (7,400–8,150 cells/ml), but became saturated at higher concentrations. The maximum growth rates of O. marina and G. dominans on Symbiodinium sp. (0.87 and 0.61/d) were much higher than those of G. moestrupii and P. kofoidii (0.11 and 0.04/d). Symbiodinium sp. did not support positive growth of G. spirale, O. rotundata, and Parastrombidinopsis sp. However, the maximum ingestion rates of P. kofoidii and Parastrombidinopsis sp. (6.7–10.0 ng C/predator/d) were much higher than those of O. marina and G. dominans on Symbiodinium sp. (1.9–2.1 ng C/predator/d). The results of the present study suggest that Symbiodinium sp. may increase or maintain the populations of some predators.     

TRANSPARENT EXOPOLYMER PARTICLES FORMATION FROM CAPSULES OF ANABAENA SPIROIDES (CYANOBACTERIA) IN CULTURE1

We report the production of large numbers of transparent exopolymer particles (TEP) from polysaccharidic capsules of Anabaena spiroides Kleb. in cultures. Two biotic pathways of TEP formation were observed: (1) fragmentation of small portions of the capsules, which occurred throughout the growth phases; and (2) transformation of the whole polysaccharidic capsules into TEP, following cellular lyses in the aging culture. Photographic documentation of these processes was performed after staining small aliquots of the samples with Alcian Blue and negative staining with India ink. Concentrations of TEP were determined in distinct culture growth phases using semiquantitative Alcian Blue staining. Concentrations of TEP increased throughout the experimental time, while Alcian Blue remaining in solution decreased. Decreasing concentrations of chl a indicated cellular death, and by the end of the experiment, TEP formed by both pathways accumulate in the culture medium. These results show that virtually all dead chains of A. spiroides are transformed into TEP in the aged culture.