Taxonomic value of a betaine lipid in Ectocarpus (Phaeophyceae) and the first record of a sexual population of E. fasciculatus for the Pacific Ocean

The betaine lipid DGTA differentiates between two species of Ectocarpus: it is present in E. fasciculatus Harvey, and lacking in E. siliculosus (Dillwyn) Lyngbye, Two ectocarpoid isolates from the coast of Chile, which could not be identified to species level, were found to belong to opposite DGTA types. Culture experiments showed that these plants were sporophytes. Their meiospores produced gametophytes of the species predicted by the lipid analysis. Promoted by this new approach, a sexual population of Ectocarpus fasciculatus has been detected for the first time in the Pacific Ocean.     

CROSSING EXPERIMENTS,LIPID COMPOSITION,AND THE SPECIES CONCEPT IN ECTOCARPUS SILICULOSUS AND E. FASCICULATUS (PHAEOPHYCEAE,ECTOCARPALES)1

Sporophytes of Ectocarpus siliculosus (Dillwyn) Lyngbye and E. fasciculatus Harvey were collected in the vicinity of Roscoff Brittany, France. Gametophytes derived from meiospores were used for intra- and interspecific crosses. Intraspecific gamete combinations gave viable zygotes, which developed into fertile sporophytes. Interspecific crosses were unsuccessful. Gamete fusions did not occur between female gametes of E. fasciculatus and male gametes of E. siliculosus. Hybrid zygotes were formed in the reciprocal combination but died soon after germination. We conclude that the two species of Ectocarpus at Roscoff represent distinct taxonomic entities, which are separated by pre- and postzygotic compatibility barriers. These biological findings are confirmed by the differential occurrence of the chemotaxonomic marker betaine-lipid diacetylglycerylhydroxymethyltrimethyl-β-alanine, which is present in our cultures of E. fasciculatus but absent in E. siliculosus.     

MOLECULAR SYSTEMATICS OF ECTOCARPUS AND KUCKUCKIA (ECTOCARPALES, PHAEOPHYCEAE) INFERRED FROM PHYLOGENETIC ANALYSIS OF NUCLEAR- AND PIASTTD-ENCODED DNA SEQUENCES

The phylogeny of Ectocarpus and Kuckuckia strains representing widely separated populations from both hemispheres was inferred from sequence analysis of the internal transcribed spacers of the nuclear ribosomal DNA (ITS 1—5.8S-ITS 2) and the spacer region in the plastid-encoded ribulose- bis -phosphate-carboxylase (RUBISCO) cistron (partial rbc L-spacer-partial rbc S ). Both sequences resulted in matching phylogenies, with the RUBISCO spacer region being most informative at the level of genera and species and the internal transcribed spacer sequences at the level of species and populations. Three major clades were formed by strains previously described by morphology and physiology as Kuckuckia, E. fasciculatus, and E. siliculosus, confirming the validity of these taxa . Ectocarpus and Kuckuckia are regarded as sibling taxa with respect to the outgroup species Feldmannia simplex, Hincksia mitchelliae, and Pilayella littoralis. The clade formed by sexual E. siliculosus strains and most asexual Ectocarpus strains was subdivided into several clades that are consistent with geographical races within E. siliculosus. The inferred phylogeny of Ectocarpus corresponds generally with results from cross-fertilization experiments, morphology, and lipid analysis. A hypothesis on the origin and dispersal of E. siliculosus suggests several natural dispersal events during periods of global cooling as well as recent and possibly anthropogenic dispersal events .     

NUTRIENTS DO NOT INFLUENCE SWIMMING BEHAVIOR OR SETTLEMENT RATES OF ECTOCARPUS SILICULOSUS (PHAEOPHYCEAE) SPORES

Spores newly released from plurilocular sporangia of Ectocarpus siliculosus (Dillw.) Lyngb. sporophytes were assayed for chemotaxis to nutrients and for settlement stimulation by nutrients. To enable these measurements with relatively small volumes and numbers of released spores, we developed a computer-assisted motion-analysis assay for spore chemotaxis and verified the results with a more standard, capillary tube chemotaxis assay. The presence of a nutrient gradient did not influence the swimming behavior of E. siliculosus spores in the motion-analysis assay, and likewise no chemotactic effect was measured in the capillary tube assay. Microplate settlement assays previously utilized with bacteria and invertebrates were adapted for use with algal spores. E. siliculosus spores settled at higher rates on a hydrophobic plastic surface than on surfaces with either positively or negatively charged hydrophilic coatings. Nutrient mixtures had no effect on the rate of spore settlement on hydrophobic surfaces.     

Contribution to the taxonomy of the Ectocarpales (Phaeophyceae) from the coast of Karachi, Pakistan

BEGUM, M. & KHATOON, N., 1992. Contribution to the taxonomy of the Ectocarpales (Phaeophyceae) from the coast of Karachi (Pakistan). The taxomony and ecology of five species belonging to the order Ectocarpales, representing three genera– Ectocarpus with one species, Hincksia with three species and Nemacystus with one species–are studied and reported as new records for the coast of Karachi, Pakistan.     

Sphondylothamnion multifidum (Huds.) Näg. in western Europe

The lipid composition of 140 clonal isolates of brown algae, covering 16 species of the genera Ectocarpus, Feldmannia and Hincksia, was analysed. All taxa contained the glycolipids monogalactosyldiacylglycerol, digalactosyldiacylglycerol and sulphoquinovosyldiacylglycerol, and the phospholipids phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol and an unidentified PX. Presence of the betaine lipid diacylglycerylhydroxymethyltrimethyl-β-alanine (DGTA) was strongly correlated with certain species in the genera Hincksia and Ectocarpus. While seven species of Hincksia contained DGTA, this lipid was absent in H. granulosa and in an unidentified Hincksia species. Due to heteromorphy of generations, species assignments in the genus Ectocarpus were made only for isolates for which the complete life history was known. We found that E. fasciculatus contains DGTA, while this lipid is absent in E. siliculosus. A collection of 40 non-sexual Ectocarpus strains included representatives with and without DGTA. The value of DGTA as a taxonomic marker in Ectocarpus and Hincksia is discussed.     

Comparisons of Two Large Phaeoviral Genomes and Evolutionary Implications

The evolution of viral genomes has recently attracted considerable attention. We compare the sequences of two large viral genomes, EsV-1 and FirrV-1, belonging to the family of phaeoviruses which infect different species of marine brown algae. Although their genomes differ substantially in size, these viruses share similar morphologies and similar latent infection cycles. In fact, sequence comparisons show that the viruses have more than 60% of their genes in common. However, the order of genes is completely different in the two genomes, suggesting that extensive recombinational events in addition to several large deletions had occurred during the separate evolutionary routes from a common ancestor. We investigated genes encoding components of signal transduction pathways and genes encoding replicative functions in more detail. We found that the two genomes possess different, although overlapping, sets of genes in both classes, suggesting that different genes from each class were lost, perhaps randomly, after the separate evolution from an ancestral genome. Random loss would also account for the fact that more than one-third of the genes in one viral genome has no counterparts in the other genome. We speculate that the ancestral genome belonged to a cellular organism that had once invaded a primordial brown algal host.     

Entry of the DNA virus, Ectocarpus fasciculatus virus type 1 (Phycodnaviridae), into host cell cytosol and nucleus

The process by which Ectocarpus fasciculatus virus type 1 (EfasV‐1) infects zoospores of its brown algal host was studied by electron microscopy. Upon virus attachment to the target cell, the integral membrane component of the viral capsid fuses with the host plasma membrane, and the 140‐nm viral DNA‐protein core enters the cytosol. Within 5 min after infection, particles resembling viral cores appeared in the nucleus. The entry mechanism of EfasV‐1 into the host nucleus remains enigmatic.     

The genome‐scale metabolic network of Ectocarpus siliculosus (EctoGEM): a resource to study brown algal physiology and beyond

Brown algae (stramenopiles) are key players in intertidal ecosystems, and represent a source of biomass with several industrial applications. Ectocarpus siliculosus is a model to study the biology of these organisms. Its genome has been sequenced and a number of post‐genomic tools have been implemented. Based on this knowledge, we report the reconstruction and analysis of a genome‐scale metabolic network for E. siliculosus, EctoGEM ( http://ectogem.irisa.fr ). This atlas of metabolic pathways consists of 1866 reactions and 2020 metabolites, and its construction was performed by means of an integrative computational approach for identifying metabolic pathways, gap filling and manual refinement. The capability of the network to produce biomass was validated by flux balance analysis. EctoGEM enabled the reannotation of 56 genes within the E. siliculosus genome, and shed light on the evolution of metabolic processes. For example, E. siliculosus has the potential to produce phenylalanine and tyrosine from prephenate and arogenate, but does not possess a phenylalanine hydroxylase, as is found in other stramenopiles. It also possesses the complete eukaryote molybdenum co‐factor biosynthesis pathway, as well as a second molybdopterin synthase that was most likely acquired via horizontal gene transfer from cyanobacteria by a common ancestor of stramenopiles. EctoGEM represents an evolving community resource to gain deeper understanding of the biology of brown algae and the diversification of physiological processes. The integrative computational method applied for its reconstruction will be valuable to set up similar approaches for other organisms distant from biological benchmark models.