Ecology,physiology and genetics of a phycodnavirus infecting the noxious bloom-forming raphidophyte <Emphasis Type="Italic">Heterosigma akashiwo</Emphasis>

Abstract:   Heterosigma akashiwo virus (HaV) is a large icosahedral virus (∼0.2 μm) harboring a double-stranded DNA (dsDNA) genome (∼294 kbp). The virus is the only member of the genus Raphidovirus in the family Phycodnaviridae. Since its first discovery, a number of ecologic, physiologic and genetic studies about HaV have been conducted; especially, the relationship between H. akashiwo and HaV in nature was studied and viral infection is now regarded as a significant factor influencing the dynamics and termination of H. akashiwo blooms. HaV infection has considerable impacts on H. akashiwo populations in both aspects of fluctuation in biomass (quantity) and changes in clonal composition (quality). Partial sequencing of the HaV genome revealed that a number of genes showed considerable similarity to those of other protist-infecting viruses; still, the phylogenetic position of HaV suggested a number of enigmas in host–virus coevolution. Here are summarized the ecology, physiology and genetics of HaV especially from the viewpoint of the host–virus relationship.     

地中海弧菌Vibrio mediterranei 117-T6的溶藻活性

很多藻类致病菌具有广谱溶藻活性。本研究发现紫菜黄斑病致病菌地中海弧菌Vibrio mediterranei 117-T6（Vm 117-T6）对赤潮异湾藻、颗石藻、叉编金藻和东海原甲藻等微藻也具有较强的溶藻活性，可使其叶绿素含量显著降低，是一株广谱性溶藻细菌。Vm 117-T6能在40 min内使赤潮异弯藻的活动能力下降，光合作用受抑，感染120 min即可导致藻体裂解并产生白色絮状沉淀。Vm 117-T6能降解卡拉胶，不能降解果胶、纤维素和几丁质。菌体、胞内及胞外提取物均具有较强的溶藻活性，其胞外溶藻物质易溶于水、不溶于石油醚和乙酸乙酯，具较强极性；耐高温、不易被活性炭吸附、乙醇处理会降低溶藻活性。Vm 117-T6在常规与易感条件下的关键差异蛋白包括大量的ABC转运蛋白、外膜蛋白、鞭毛蛋白及少量Toxin。这些研究结果提示Vm 117-T6毒力效应物中含有极性非蛋白质类物质，且与毒力因子转运、分泌以及细胞黏附相关的蛋白可能在其毒力作用中发挥重要作用。上述研究结果表明：多种溶藻机制参与了Vm 117-T6的溶藻过程。     

Characteristics of the marine environment and algal blooms in Gamak Bay

This study was conducted to gain insight into the characteristics of algal blooms in relation to the marine environment of Gamak Bay. From the first known occurrence of algal blooms in 1984 until 2006, 23 causal species have been identified, the most common ones being Prorocentrum sp., Cochlodinium polykrikoides, Chaetoceros sp., Skeletonema costatum, and Heterosigma akashiwo. A principal component analysis indicated that blooms of these species develop under different conditions in terms of water temperature, salinity, precipitation, and insolation. Field data showed Cochlodinium polykrikoides to be favored by high temperatures and to be euryhaline, whereas Skeletonema costatum appeared to be eurythermal and euryhaline. Prorocentrum sp. and Chaetoceros sp. appeared to be stenothermal and stenohaline. Finally, Heterosigma akashiwo appeared at the lowest temperature and highest salinity of the five species and was classified here as stenothermal and stenohaline.     

Fe~(3+)对赤潮异弯藻(Heterosigma akashiwo)生长的影响

为探索Fe3 与赤潮发生的关系,采用模拟生长方法研究了Fe3 对赤潮异弯藻(Heterosigmaakashiwo)生长的影响。Fe3 是赤潮异弯藻生长的限制因子,低于0.01μmol·L-1会抑制该藻的生长,在0.01￣0.05μmol·L-1时赤潮异弯藻的比生长速率与Fe3 浓度成正比关系;赤潮异弯藻的最大生长速率μm-Fe=0.2728,Ks-Fe=0.0169μmol·L-1。EDTA是赤潮异弯藻生长的限制因子,EDTA对于赤潮异弯藻生长的限制浓度是0.013μmol·L-1,EDTA浓度小于0.013μmol·L-1时,赤潮异弯藻的生长明显受到抑制;EDTA浓度大于0.013μmol·L-1时,赤潮异弯藻的比生长速率与EDTA浓度成正比关系(μ-EDTA=2.0742x-0.0114,r2=0.9248),浓度为0.13μmol·L-1时藻的生长速率接近最大值,赤潮异弯藻的最大生长速率μm-EDTA=0.3114,Ks-EDTA=0.1160μmol·L-1。探讨了不同Fe3 /EDTA比值对赤潮异弯藻生长的影响,Fe3 /EDTA比值为0.2时藻细胞生长速率达到最大,表明比值为0.2时最适合赤潮异弯藻的生长。因此,赤潮异弯藻适合在Fe3 、EDTA浓度分别大于0.05、0.13μmol·L-1、Fe3 /EDTA=0.2的条件下生长。     

赤潮异弯藻对鳀鱼早期发育的影响

就赤潮异弯藻(Heterosigma akashiwo)藻液及各组分对鳀鱼(Engraulis ja ponicus)早期发育阶段的影响进行了研究。并就鳃鱼早期发育过程中对赤潮异弯藻的敏感性时期作了探讨。实验结果表明，原肠期前的发育卵和初孵仔鱼对赤潮异弯藻较其他发育阶段更为敏感。在同等条件下藻细胞内容物对鳃鱼早期发育各阶段的毒性最大，其次是藻细胞碎片和藻液，去藻过滤液的毒性最小。暴露在高浓度90000c／ml藻细胞内容物中，96h后仔鱼的存活率为4％；而在同浓度的去藻过滤液中，96h后仔鱼的存活率为75％。藻细胞内容物和藻细胞碎片对鳃鱼仔鱼96hI。C∞分别为2818、6760c／mL．     

孔石莼和赤潮异弯藻相互作用的初步研究

选用大型海藻——孔石莼Ulvapertusa和赤潮微藻——赤潮异弯藻Heterosigmaakashiwo为试验材料,在实验室条件下研究了藻体、培养液滤液和胞内物质对生长相互作用的影响。结果表明：孔石莼和赤潮异弯藻二者之间存在克生效应,孔石莼培养液滤液和胞内物质对赤潮异弯藻生长有显著的抑制作用（P〈0．01）,而赤潮异弯藻培养液滤液和胞内物质对孔石莼生长亦有显著的抑制作用（P〈O．01）。可以推测：孔石莼可能是通过分泌次生物质来抑制赤潮异弯藻的生长,而赤潮异弯藻可能是通过细胞的直接接触和分泌次生物质完成对孔石莼生长的抑制,其抑制物均存在于藻体和培养液中。     

海州湾海域一次赤潮异弯藻赤潮与环境因子的关系

通过对2008年5月发生在连云港海州湾海域的一次赤潮异弯藻赤潮的跟踪监测,并研究其赤潮发生与环境因子的关系,得出:良好的水文气象条件,丰富的营养盐为赤潮的爆发及维持提供了基础。赤潮的发生,导致pH值、盐度、溶解氧、叶绿素a、营养盐等环境因子都发生了变化。此次赤潮异弯藻赤潮主要吸收硝酸盐和铵盐,磷酸盐是其生长的限制因子。高氮磷比也是赤潮异弯藻生长的重要调控因子。     

浒苔对赤潮异湾藻的克生作用

研究了浒苔对赤潮微藻—— 赤潮异湾藻生长的克生效应。结果表明, 浒苔新鲜组织对赤潮异湾藻的生长具有强烈的克生效应; 一次性添加浒苔培养过滤液对赤潮异湾藻生长没有显著的抑制作用, 而半连续添加浒苔培养过滤液对赤潮异湾藻生长具有显著的克生作用; 浒苔干粉末和甲醇抽提液均对赤潮异湾藻的生长产生显著的抑制作用。试验结果表明, 抑制赤潮异湾藻生长的物质很可能更多地存在于浒苔组织内, 向环境中分泌的克生物质较少。因而, 克生物质的连续分泌是有效克制赤潮异湾藻生长的关键。同时, 克生作用存在着明显的浓度效应, 当抑制物浓度达到一定阈值才表现出明显的克生作用, 在阈值之上浓度越高克生作用越强。     

Molecular identification of red tide-causing microalga Heterosigma akashiwo strains based on their chloroplast DNA sequences

ABSTRACT:   In order to establish genetic signatures for intraspecific identification, parts of the genes rbcL , rbcS and psbA and their intergenic spacer (IGS) regions were amplified by polymerase chain reaction (PCR) from the chloroplast genomes of Heterosigma akashiwo strains isolated from Japan. A transfer RNA-Leu gene trnL and a hypothetical gene cfxQ , which is related to ribulose bisphosphate carboxylase/oxygenase expression, were found in the upstream region of the rbcL gene and in the rbcS-psbA IGS region, respectively. All the gene-coding regions and the IGS regions between rbcL and rbcS showed the same sequences among the strains tested. In contrast, the rbcL upstream regions and the rbcS-cfxQ IGS regions showed some differences such as nucleotide substitutions, duplications and inversions between NIES-5 and the other strains. Based on these sequence data, five genetic signatures were established and their simple and rapid detection by means of strain-specific PCR primers and PCR-restriction fragment length polymorphism techniques was examined. The results suggested the usefulness of these genetic signatures and techniques for the discrimination of H. akashiwo populations.     

营养因子对赤潮异弯藻生长的影响

以赤潮异弯藻为材料,采用正交试验方法,研究了氮、磷、微量元素混合液和维生素混合液对赤潮异弯藻生长的影响。试验结果表明,在对数期和稳定期,4种营养因子中对赤潮异弯藻生长影响的顺序为磷>维生素>氮≥微量元素;在衰亡期,营养因子中对赤潮异弯藻生长影响的顺序为氮>磷>维生素>微量元素。在对数期,氮、磷、微量元素和维生素等营养因子的最适浓度分别为880、18、10.55、0.32μmol/L;在稳定期和衰亡期,最适浓度分别为2640、108、21.1、0.96μmol/L。各营养因子在不同时期均对赤潮异弯藻的增殖具有显著影响(P<0.01)。