Development and physiology of the brown alga Ectocarpus siliculosus: two centuries of research

Brown algae share several important features with land plants, such as their photoautotrophic nature and their cellulose-containing wall, but the two groups are distantly related from an evolutionary point of view. The heterokont phylum, to which the brown algae belong, is a eukaryotic crown group that is phylogenetically distinct not only from the green lineage, but also from the red algae and the opisthokont phylum (fungi and animals). As a result of this independent evolutionary history, the brown algae exhibit many novel features and, moreover, have evolved complex multicellular development independently of the other major groups already mentioned. In 2004, a consortium of laboratories, including the Station Biologique in Roscoff and Genoscope, initiated a project to sequence the genome of Ectocarpus siliculosus, a small filamentous brown alga that is found in temperate, coastal environments throughout the globe. The E. siliculosus genome, which is currently being annotated, is expected to be the first completely characterized genome of a multicellular alga. In this review we look back over two centuries of work on this brown alga and highlight the advances that have led to the choice of E. siliculosus as a genomic and genetic model organism for the brown algae.     

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模式标本产地：巴布亚新几内亚（？）。Habit and Locality：在潮下带附着于 Sargdesum sp．体上。标本采自海甫省文昌县     

REFLECTIVE PROPERTIES OF THE STIGMA IN MALE GAMETES OF ECTOCARPUS SILICULOSUS (PHAEOPHYCEAE) STUDIED BY CONFOCAL LASER SCANNING MICROSCOPY1

The reflection properties of the stigma in male gametes of Ectocarpus siliculosus (Dillw.) Lyngbye were investigated using confocal laser scanning microscopy in the epireflection contrast mode. The complex reflection pattern obtained after optical xy (horizontal) and xz (vertical) sectioning was consistent with stigma ultrastructure as revealed by serial thin sections. The intensity and pattern of the reflection signal varied with the orientation of the cell/stigma to the incident laser light. Maximal reflection occurred only in approximately normal orientation of the stigma to the light source. Focusing of reflected light from an elongated concave depression of the stigma on the region of the flagellar swelling was observed in xy and xz sections of living and fixed gametes. The results indicate the importance of mechanisms (focusing) other than quarter-wave interference reflection in signal amplification by the eyespot of flagellate algae.     

An immunofluorescence study on lectin binding sites in gametes of Ectocarpus siliculosus (Ectocarpales, Phaeophyceae)

The distribution of binding sites for the lectins WGA, DSA. RCA I, PNA, AAA, MAA. SNA, GNA. and Con A in gametes of both sexes of the brown alga, Ectocarpus siliculosus (Dillw.) Lyngbye, was investigated by fluorescence microscopy. Digoxigenin-conjugated lectins and an FITC-anti-digoxigenin antibody were used as a high sensitivity detection system. Organelles and other distinct cellular domains could be distinguished by their binding specificities. Glycoconjugates associated with one flagellum were found to be associated with the axoneme by lectin binding to isolated flagellar apparatuses. In addition, changes in the distribution of carbohydrate epitopes during the attachment of gametes to the substratum were revealed by differential lectin binding.     

Genome-based phylogeny of dsDNA viruses by a novel alignment-free method

Sequence alignment is not directly applicable to whole genome phylogeny since several events such as rearrangements make full length alignments impossible. Here, a novel alignment-free method derived from the standpoint of information theory is proposed and used to construct the whole-genome phylogeny for a population of viruses from 13 viral families comprising 218 dsDNA viruses. The method is based on information correlation (IC) and partial information correlation (PIC). We observe that (i) the IC-PIC tree segregates the population into clades, the membership of each is remarkably consistent with biologist's systematics only with little exceptions; (ii) the IC-PIC tree reveals potential evolutionary relationships among some viral families; and (iii) the IC-PIC tree predicts the taxonomic positions of certain “unclassified” viruses. Our approach provides a new way for recovering the phylogeny of viruses, and has practical applications in developing alignment-free methods for sequence classification.     

Cadmium adsorption by non-living biomass of the semi-macroscopic brown alga,Ectocarpus siliculosus,grown in axenic mass culture and localisation of the adsorbed Cd by transmission electron microscopy

Non-living, freeze-dried material of the brown algaEctocarpus siliculosus (Phaeophyceae) demonstrated high equilibrium uptake of Cd from aqueous solutions (Fehrmann & Pohl, 1993). The alga was grown in 250-L photobioreactors under various growth conditions (light, salinity and nutrient concentrations) in order to obtain larger quantities of biomass and to improve its Cd adsorption capacity. To derive further knowledge on the biosorbant phenomenon different adsorption parameters such as pH for the sorption process and kinetics of Cd adsorption were tested. The maximum adsorption capacity of the freeze-dried biomass exceeded 41 mg Cd per g biomass. After repeated addition of low Cd concentrations the maximum adsorption capacity was lower (31.4 mg Cd per g biomass). In comparison with other adsorbing materials (activated carbon, silica gel, siliceous earth)E. siliculosus showed significantly higher adsorption capacity. Desorption of deposited Cd with 0.1 M HCl resulted in no changes of the adsorption capacity through five subsequent adsorption-/desorption-cycles. Hence, driedE. siliculosus appears to be an efficient material for the elimination of Cd from industrial waste water.Transmission electron microscopic investigations showed an electron dense area in the outer surface layers of the cell wall after Cd adsorption indicating the most likely location of Cd fixation.Author for correspondence     

Pathogens of brown algae: culture studies of Anisolpidium ectocarpii and A. rosenvingei reveal that the Anisolpidiales are uniflagellated oomycetes

Using laboratory cultures, we have documented the life cycle of Anisolpidium ectocarpii, a pathogen of Ectocarpus and other filamentous brown algae, and presented preliminary observations on Anisolpidium rosenvingei, a pathogen of Pylaiella littoralis. Consistent with earlier reports, the zoospores of both species have a single anterior flagellum, which justified the placement of Anisolpidium amongst the Hyphochytriales (Hyphochytridiomycota). We have also shown that A. ectocarpii can complete its infection cycle in a broad selection of species from various brown algal orders, whereas A. rosenvingei seemingly exhibits a strict specificity for unilocular sporangia of P. littoralis. Unexpectedly, nuclear (18S rRNA) and mitochondrial (cox1, cox2) markers regroup A. ectocarpii and A. rosenvingei, into a hitherto unrecognized monophyletic clade within the oomycetes (Oomycota), most closely related to the Olpidiopsidales. The Anisolpidium genus is therefore entirely distinct from the Hyphochytridiomycota and represents the first confirmed instance of an anteriorly uniciliate oomycete. Finally, we suggest that a valid morphological criterion to separate true hyphochytrids from oomycetes is the timing of zoospore cleavage. Given the evidence, we propose to transfer the Anisolpidiales from the Hyphochytriales to the Oomycetes.     

PASSAGE OF A MARINE BROWN ALGAL DNA VIRUS FROM ECTOCARPUS FASCICULATUS (ECTOCARPALES,PHAEOPHYCEAE) TO MYRIOTRICHIA CLAVAEFORMIS (DICTYOSIPHONALES,PHAEOPHYCEAE): INFECTION SYMPTOMS AND RECOVERY1

A dsDNA virus (EfasV-1) isolated from Ectocarpus fasciculatus Harvey infected Myriotrichia clavaeformis Harvey, a species belonging to a different brown algal order. The virus did not complete its infection cycle in the foreign host but caused infertility due to malformed reproductive structures. After some time in culture, the host's reproductive capacity was sometimes restored with concomitant loss of at least part of the viral genome. This incidence of interordinal virus transfer is discussed in relation to possibilities for virus-mediated horizontal gene transfer in brown algae.     

Influence of carbon supply on the circadian rhythmicity of photosynthesis and its stimulation by blue light in Ectocarpus siliculosus: clues to the mechanism of inorganic carbon acquisition in lower brown algae

Stimulation or light-saturated rates of photosynthesis in Ectocarpus siliculosus (Dillwyn) Lyngb. by blue light was eliminated by increasing dissolved inorganic carbon (DIC) or by lowering pH in natural seawater. The amplitude of the circadian rhythm of photosynthesis was also diminished under these conditions, and the pH compensation points in a closed system were higher in the presence of blue light and during the circadian day. These observations suggest that blue light and the circadian clock regulate the activity of a carbon acquisition system in these plants. The inhibitor of external carbonic anhydrase, acetazolamide, reduced overall rates of photosynthesis by only about 30%, but ethoxyzolamide suppressed the circadian rhythm of photosynthesis almost completely and markedly reduced the duration of responses to blue light pulses. Similar patterns were obtained when photosynthesis was measured in strongly limiting DIC concentrations (0–0.5 mol m^?3). Since blue light stimulated photosynthesis under these conditions of strong carbon limitation, we suggest that blue light activates the release of CO₂ from an internal CO₂ store. We propose a metabolic pathway with similarities to that of CAM plants. Non-photosynthetic fixation leads to the accumulation of a storage metabolite. The circadian clock and blue light control the mobilization of CO₂ at the site of decarboxylation of this metabolite. In the presence of continuous blue light the pathway is proposed to cycle and act as a pump for CO₂ into the chloroplasts. This hypothesis helps to explain a number of previously reported peculiarities of brown algal photosynthesis.     

Effect of Extracellular Ca2+ and Ca2+-Antagonists on the Movement and Chemoorientation of Male Gametes of Ectocarpus siliculosus (Phaeophyceae)

Chemoorientation in male gametes of Ectocarpus siliculosus in response to sexual pheromones is effected by two distinct mechanisms, chemokinesis and chemoklinotaxis. These are characterized by a strongly asymmetric bending pattern of the anteriorly-directed flagellum and transient unilateral bending of the hind flagellum, respectively. Removal of extracellular Ca²⁺ showed that normal flagellar movement and chemokinesis require millimolar concentrations of Ca²⁺ in the medium. The response to pheromones is strongly inhibited by La³⁺, whereas the Ca²⁺-channel drugs, verapamil and nifedipine, have only little effect. Nifedipine nethertheless effectively inhibited accumulation at pheromone sources. These results are interpreted as an indication for the involvement of two pharmacologically distinct Ca²⁺-channels in chemokinesis and chemoklinotaxis. The calmodulin-antagonist, trifluoperazine, induces, at low concentrations, the same flagellar response in chemokinesis as the pheromone, the mechanism of action remaining unknown.