Inorganic carbon acquisition in red tide dinoflagellates

Carbon acquisition was investigated in three marine bloom-forming dinollagellates-Prorocentrum minimum, Heterocapsa triquetra and Ceratium lineatum. In vivo activities of extracellular and intracellular carbonic anhydrase (CA), photosynthetic O2 evolution, CO2 and HCO3- uptake rates were measured by membrane inlet mass spectrometry (MIMS) in cells acclimated to low pH (8.0) and high pH (8.5 or 9.1). A second approach used short-term 14C-disequilibrium incubations to estimate the carbon source utilized by the cells. All three species showed negligible extracellular CA (eCA) activity in cells acclimated to low pH and only slightly higher activity when acclimated to high pH. Intracellular CA (iCA) activity was present in all three species, but it increased only in P. minimum with increasing pH. Half-saturation concentrations (K1/2) for photosynthetic O2 evolution were low compared to ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) kinetics. Moreover, apparent affinities for inorganic carbon (Ci) increased with increasing pH in the acclimation, indicating the operation of an efficient CO2 concentration mechanism (CCM) in these dinoflagellates. Rates of CO2 uptake were comparably low and could not support the observed rates of photosynthesis. Consequently, rates of HCO3- uptake were high in the investigated species, contributing more than 80% of the photosynthetic carbon fixation. The affinity for HCO3- and maximum uptake rates increased under higher pH. The strong preference for HCO3- was also confirmed by the 14C-disequilibrium technique. Modes of carbon acquisition were consistent with the 13C-fractionation pattern observed and indicated a strong species-specific difference in leakage. These results suggest that photosynthesis in marine dinoflagellates is not limited by Ci even at high pH, which may occur during red tides in coastal waters.     

Effects of toxic Alexandrium species on the survival and feeding rates of brine shrimp, Artemia salina

Zooplankton is an important link between phytoplankton and higher consumers in the marine food chain. To investigate the harmful effects of the toxic dinoflagellate Alexandrium species on zooplankton, 4 strains of Alexandrium spp., isolated from the Chinese coast, were used to test the species' effects on the survival and feeding rates of the brine shrimp, Artemia salina. The experiment was designed to assess the response of A. salina in each stage of its life cycle: nauplii, metanauplii, and adult. Each experiment was conducted in a 500 ml treatment that was added. The toxic treatments consisted of single strains of A. minutum, A. catanella, and A. tamarense (Nanhai and Donghai strain), while non-toxic species (dinoflagellate Prorocentrum donghaiense and diatom Chaetoceros minutissimus) were used as control treatments. An additional phytoplankton treatment consisted of, a mixture of A. tamarense (Nanhai strain) and P. donghaiense. Alexandrium spp. species were found to have lethal effects on the brine shrimp at a density of 2000 cells/ml. All the brine shrimps died within 24-168 hours of inoculation with the 4 treatments each containing single toxic Alexandrium species. During the feeding experiment, toxic Alexandrium spp. caused a reduction in the feeding rates in all the three stages of the life cycle of A. salina, whereas this response was not obvious in the treatment involving the nontoxic species P. donghaiense. The body surface of the brine shrimp that were fed on Alexandrium species was consistently covered by a sticky floc. Mortality of A. salina was observed to increase with the occurrence of the floc. The toxicity of the paralytic shellfish poisons (PSP) produced by the Alexandrium species was not significantly correlated with the survival or the feeding rate of the brine shrimp. When A. tamarense was mixed with P. donghaiense, the lethal effect of A. tamarense decreased, as shown by an increase in the survival and the feeding rates of the brine shrimp. A. salina metanauplii were found at the life stage most sensitive to the toxic algae and hunger. In summary, toxic Alexandrium spp. were found to have lethal effects on A. salina and to restrain the brine shrimp's feeding rate. Nontoxic Prorocentrum mitigated the toxicity of Alexandrium to a certain extent. The results also imply that the sticky material on the surface of the body of the brine shrimp may have been an important lethal factor rather than the PSP toxins.     

东海原甲藻与中肋骨条藻的种间竞争特征

对东海原甲藻和中肋骨条藻按照起始Chl-a比1∶5、1∶1和5∶1进行了f/2条件下的共培养实验,以探讨这两种藻的种间竞争特征。实验结果表明在共培养体系中,中肋骨条藻完全占优势,而东海原甲藻的生长受到明显的抑制。应用Lotka-Volterra种间竞争模型对共培养实验进行模拟的结果表明,东海原甲藻与中肋骨条藻的种间竞争结果与初始密度配比无关,中肋骨条藻总会竞争胜过东海原甲藻。为了探讨他感作用对东海原甲藻和中肋骨条藻种间竞争的影响,采用了中肋骨条藻的无藻细胞滤液来进行培养实验。实验结果显示,中肋骨条藻滤液对东海原甲藻及其本身的生长均无明显影响,这表明他感作用并非中肋骨条藻获得优势的主要竞争方式。     

塔玛亚历山大藻和东海原甲藻对褶皱臂尾轮虫种群数量的影响

通过对2002年5月东海赤潮原因种一东海原甲藻和亚历山大藻的单一藻种和两种藻混合情况下对褶皱臂尾轮虫种群数量影响的实验研究,发现塔玛亚历山大藻(ATHK)对轮虫有致死作用,其48hLC50为1300cell·ml^-1．藻的各组分毒性比较研究表明,只有藻液和藻细胞具有这种毒害作用,藻在早期生长阶段的毒害作用较强,毒性大小与藻细胞活性相关．东海原甲藻在高密度(4×10^4、5×10^4、10×10^4cell·ml^-1)时对轮虫种群数量在第5d时开始有影响;东海原甲藻在低密度(1×10^4、2×10^4、3×10^4cell·ml^-1)时,轮虫能够以其为食并进行生长繁殖．两种藻混合情况下,东海原甲藻能够减轻塔玛亚历山大藻对轮虫的毒害作用．实验结果表明,此次赤潮对东海的微型浮游动物种群能够产生一定的影响．     

PROROCENTRUM BIMACULATUM SP. NOV. (DINOPHYCEAE,PROROCENTRALES), A NEW BENTHIC DINOFLAGELLATE SPECIES FROM KUWAIT (ARABIAN GULF)1

A new benthic dinoflagellate species, Prorocentrum bimaculatum sp. nov., is studied from Kuwait’s marine sediments, based on detailed morphological and molecular data. Cells are large, oblong oval in shape. They are 49.9–55.3 μm long and 38.4–43.2 μm wide. The ornamentation of this new species is peculiar, and characterized by smooth valves with large pores (0.32–0.50 μm) scattered on their surface, except in two circular patches of ～15 μm in diameter, devoid of ornamentation and located on both sides of the valve centers. The periflagellar area is widely triangular, located in a moderate excavation of the right valve, and comprises nine platelets. The intercalary band of P. bimaculatum is smooth. The molecular phylogenetic position of this new taxon was inferred from SSU and LSU rDNA genes. In both phylogenetic analyses, P. bimaculatum branched with high support with Prorocentrum consutum and formed a clade sister to the one including P. lima and related species such as P. arenarium, P. belizeanum, P. hoffmannianum, and P. maculosum. From the phylogenetic study, since most species related to P. bimaculatum are known for their toxic effects and production of okadaic acid, this new species can be considered as a potential toxin producer, but this has to be analyzed.     

慢原甲藻——南海热带附生甲藻新记录

从海南陵水新村港分离出1株附生原甲藻,在光学显微镜和扫描电子显微镜下进行形态学特征分析,并结合核糖体18S rRNA基因序列分析,鉴定为慢原甲藻(Prorocentrum rhathymum),为国内首次报道。国内曾将该种与墨西哥原甲藻(Prorocentrum mexicanum)归为同种异名。     

Are Prorocentrum hoffmannianum and Prorocentrum belizeanum (DINOPHYCEAE,PROROCENTRALES), the same species? An integration of morphological and molecular data

The taxonomic assignment of Prorocentrum species is based on morphological characteristics; however, morphological variability has been found for several taxa isolated from different geographical regions. In this study, we evaluated species boundaries of Prorocentrum hoffmannianum and Prorocentrum belizeanum based on morphological and molecular data. A detailed morphological analysis was done, concentrating on the periflagellar architecture. Molecular analyses were performed on partial Small Sub‐Unit (SSU) rDNA, partial Large Sub‐Unit (LSU) rDNA, complete Internal Transcribed Spacer Regions (ITS1‐5.8S‐ITS2), and partial cytochrome b (cob) sequences. We concatenated the SSU‐ITS‐LSU fragments and constructed a phylogenetic tree using Bayesian Inference (BI) and maximum likelihood (ML) methods. Morphological analyses indicated that the main characters, such as cell size and number of depressions per valve, normally used to distinguish P. hoffmannianum from P. belizeanum, overlapped. No clear differences were found in the periflagellar area architecture. Prorocentrum hoffmannianum and P. belizeanum were a highly supported monophyletic clade separated into three subclades, which broadly corresponded to the sample collection regions. Subtle morphological overlaps found in cell shape, size, and ornamentation lead us to conclude that P. hoffmanianum and P. belizeanum might be considered conspecific. The molecular data analyses did not separate P. hoffmannianum and P. belizeanum into two morphospecies, and thus, we considered them to be the P. hoffmannianum species complex because their clades are separated by their geographic origin. These geographic and genetically distinct clades could be referred to as ribotypes: (A) Belize, (B) Florida‐Cuba, (C1) India, and (C2) Australia.     

COMPLEX GENE STRUCTURE OF THE FORM II RUBISCO IN THE DINOFLAGELLATE PROROCENTRUM MINIMUM (DINOPHYCEAE)1

We analyzed the unusually complex organization of the nuclear‐encoded (form II) RUBISCO gene in the dinoflagellate Prorocentrum minimum (Parvillard) Schiller by intensive genomic DNA and cDNA sequencing and Western blotting. Over 10 transcribed units (TUs) were detected, which varied dramatically in their 3′ untranslated region. Each TU appeared to contain four tandem copies of the RUBISCO coding region (1.46 kb each; coding unit, or CU) interspersed by a 63‐bp spacer; the four CUs in each TU were cotranscribed and apparently cotranslated to a tetrameric polyprotein that may undergo successive cleavage steps to yield mature RUBISCO. By means of real‐time PCR analysis, it was estimated that each of the P. minimum genome harbored 148±16 CUs. Although nucleotide sequences varied by 1%–9% among the detected CUs, their inferred amino acid sequences were essentially identical. Our results suggest that the complex structure of Pmrbc has been derived from extensive and repeated gene duplications, an evolutionary process that has also been observed for other dinoflagellate genes.     

NOTE PROROCENTRUM LIMA (DINOPHYCEAE) IN WATERS OF THE GREAT SOUTH CHANNEL NEAR GEORGES BANK

A 0–10 m plankton tow collected at one station in the Great South Channel near Georges Bank in June 1994 was rich in dinoflagellates, with the usually epibenthic Prorocentrum lima (Ehrenberg) Dodge present as the dominant species. Temperature and salinity profiles suggest that the phytoplankton population at this station may have been advected from waters on the southern flank of Georges Bank. This is the first unequivocal report of P. lima in the plankton community of the Great South Channel and its vicinity.