Host-virus interactions in marine brown algae

Ectocarpus-like marine brown algae are frequently parasitized by polyhedric DNA viruses. Infected hosts have been studied in unialgal and axenic cultures, and the present state of knowledge is summarized in regard to stage-specific virus expression, discharge and survival time of virus particles, infection mechanism, association with host's nuclear genome, passage of the virus genome through mitosis and meiosis of the host, suppression of symptoms and spontaneous recovery of infected plants, host specificity and intergeneric transmission, vitality of infected plants, pandemic occurrence of virus infections, molecular data on Ectocarpus and Feldmannia viruses, and algal DNA-viruses as potential vectors for gene transfer. A scheme for the nomenclature of brown algal viruses is proposed.     

A Novel Evolutionary Strategy Revealed in the Phaeoviruses

Phaeoviruses infect the brown algae, which are major contributors to primary production of coastal waters and estuaries. They exploit a Persistent evolutionary strategy akin to a K- selected life strategy via genome integration and are the only known representatives to do so within the giant algal viruses that are typified by r- selected Acute lytic viruses. In screening the genomes of five species within the filamentous brown algal lineage, here we show an unprecedented diversity of viral gene sequence variants especially amongst the smaller phaeoviral genomes. Moreover, one variant shares features from both the two major sub-groups within the phaeoviruses. These phaeoviruses have exploited the reduction of their giant dsDNA genomes and accompanying loss of DNA proofreading capability, typical of an Acute life strategist, but uniquely retain a Persistent life strategy.     

Exploring Core Response Mechanisms to Multiple Environmental Stressors Via A Genome‐Wide Study in the Brown Alga Saccharina japonica (Laminariales,Phaeophyceae)

Saccharina japonica is an important large brown alga and a major component of productive beds on the northwest coast of the Pacific Ocean. Abiotic stress response mechanisms are receiving considerable attention because global climate change is increasing their abiotic stress levels. However, our knowledge of how S. japonica broadly responds to stress is limited. In this study, we investigated the S. japonica responsive genes underlying acclimation to diverse stressors of acidification, high light, high temperature, hypersalinity, and hyposalinity and identified 408 core genes constantly and differentially expressed in response to all stressors. Our results confirm that stressors had strong effects on genes participating in photosynthesis, amino acid metabolism, carbohydrate metabolism, halogen metabolism, and reactive oxygen species defense. These findings will improve our understanding of brown algal response mechanisms linked to environmental stress and provide a list of candidate genes for improving algal stress tolerance in light of environmental stress in future studies.     

A NEW BROWN ALGAL ORDER,ISHIGEALES (PHAEOPHYCEAE), ESTABLISHED ON THE BASIS OF PLASTID PROTEIN‐CODING rbcL,psaA, AND psbA REGION COMPARISONS1

The brown algal family Ishigeaceae currently includes a single genus, Ishige Yendo, with two species. The relationship of the family to other brown algal lineages is less studied in terms of their plastid ultrastructure and molecular phylogeny. We determined the sequences of rbcL from four samples of the two Ishige species and nine putative relatives and the psaA and psbA sequences from 37 representatives of the brown algae. Analyses of individual and combined data sets resulted in similar trees; however, the concatenated data gave greater resolution and clade support than each individual gene. In all the phylogenies, the Phaeophyceae was well resolved, the Ectocarpales being placed in a terminal position and the Ishigeaceae ending up in a basal position. From our ultrastructural study, we concluded that the pyrenoid is absent in the Ishigeaceae, despite the presence of a rudimentary pyrenoid in I. okamurae. These results suggest that the Ishigeaceae is an early diverging brown lineage. Our molecular and morphological data, therefore, lead us to exclude the Ishigeaceae from the Ectocarpales s.l., which have an elaborate pyrenoid, and to propose its own order Ishigeales ord. nov. The Ishigeales is distinguished by oligostichous structure of thalli, phaeophycean hairs formed within cryptostomata, unilocular sporangia transformed from terminal cortical cells, and plurilocular sporangia lacking sterile terminal cells. This study is the first to document the utility of the psaA and psbA sequences for brown algae and also the first report on the multigene phylogeny of the Phaeophyceae based on three protein‐coding plastid genes.     

Viral inosine triphosphatase: A mysterious enzyme with typical activity,but an atypical function

Plant viruses typically have highly condensed genomes, yet the plant-pathogenic viruses Cassava brown streak virus, Ugandan cassava brown streak virus, and Euphorbia ringspot virus are unusual in encoding an enzyme not yet found in any other virus, the “house-cleaning” enzyme inosine triphosphatase. Inosine triphosphatases (ITPases) are highly conserved enzymes that occur in all kingdoms of life and perform a house-cleaning function by hydrolysing the noncanonical nucleotide inosine triphosphate to inosine monophosphate. The ITPases encoded by cassava brown streak virus and Ugandan cassava brown streak virus have been characterized biochemically and are shown to have typical ITPase activity. However, their biological role in virus infection has yet to be elucidated. Here we review what is known of viral-encoded ITPases and speculate on potential roles in infection with the aim of generating a greater understanding of cassava brown streak viruses, a group of the world's most devastating viruses.     

Latitudinal variation in intertidal algal community structure: the influence of grazing and vegetative propagation

Summary The hypothesis that sea urchin grazing and interactions with turf-forming red algae prevent large brown algae from forming an extensive canopy in the low intertidal zone of southern California was tested with field experiments at two study sites. Experimental removal of sea urchins resulted in rapid algal recruitment. Crustose coralline algae which typically dominate the substratum in areas with dense urchin populations were quickly overgrown by several species of short-lived green, brown and red algae. The removal of urchins also significantly increased the recruitment of two long-lived species of large brown algae (Egregia laevigata and Cystoseira osmundacea at one study site and E. laevigata and Halidrys dioica at the other). The experimental plots at both sites were eventually dominated by perennial red algae.A two-factorial experiment demonstrated that sea urchin grazing and preemption of space by red algae in areas where urchins are less abundant are responsible for the rarity of large brown algae in the low intertidal of southern California. The three dominant perennial red algae, Gigartina canaliculata, Laurencia pacifica and Gastroclonium coulteri, recruit seasonally from settled spores but can rapidly fill open space with vigorous vegetative growth throughout the year. These species encroach laterally into space created by the deaths of large brown algae or by other disturbances. Once extensive turfs of these red algae are established further invasion is inhibited. This interaction of algae which proliferate vegetatively with algae which recruit only from settled spores is analogous to those which occur between solitary and colonial marine invertebrates and between solitary and cloning terrestrial plants.It is suggested that a north-south gradient in the abundance of vegetatively propagating species, in grazing intensity and in the frequency of space-clearing disturbances, may account for latitudinal variation in intertidal algal community structure along the Pacific coast of North America.     

Scales of dispersal among hosts in a herbivorous marine amphipod

Abstract The spatial arrangement of plants may constrain the expression of herbivore preferences due to interaction between the scales of herbivore mobility and vegetation structure. I tested the hypothesis that the presence of the herbivorous marine amphipod Peramphithoe parmerong (Ampithoidae) on a low‐preference, poor‐quality host (the brown alga Padina crassa) was due to limited dispersal and the clumped nature of algal distributions. In contrast to limited dispersal in laboratory assays, amphipods rapidly colonized vacant algae in the field with natural densities being achieved within 1 day. These high rates of colonization did not decline with increasing distance from existing algal beds over the spatial scales separating Pa. crassa from the higher‐quality host algae (Sargassum spp.). Thus, the spatial arrangement of host algae did not interact with herbivore mobility to constrain host choices.     

Isolation of antifouling active pyroglutamic acid,triethyl citrate and di-<Emphasis Type="Italic">n</Emphasis>-octylphthalate from the brown seaweed <Emphasis Type="Italic">Ishige okamurae</Emphasis>

Three antifouling active compounds of L-pyroglutamic acid (PGA), triethyl citrate (TEC) and di-n-octylphthalate (DNOP) were isolated from the brown seaweed Ishige okamurae. Approximately 2.8 mg PGA, 1.7 mg TEC, and 2.0 mg DNOP were isolated from 600 g of I. okamurae powder. The concentrations of PGA, TEC, and DNOP required to cause foot repulsion in 50% of mussels (RD₅₀) were 9, 26, and 0.08 mM, respectively. The PGA, TEC, and DNOP concentrations required to inhibit 50% attachment of algal spores (ID₅₀) were 24, 50 and 0.1 mM, respectively. These compounds showed stable antifouling activities against mussel and algal spore attachment.     

STRUCTURE AND FUNCTION OF BENTHIC ALGAL COMMUNITIES IN AN EXTREMELY ACID RIVER1

The composition of algal species and pigments and the structural and functional characteristics of the algal community were investigated in an acid stream of southwestern Spain, the Río Tinto. The algal community had low diversity and showed few seasonal differences. It was mainly made up of Klebsormidium flaccidum Kütz. (Silva, Mattox & Blackwell) that produced long greenish or purplish filaments, Pinnularia acoricola Hust. (producing brown patches) and Euglena mutabilis Schmitz. The algal filaments made up a consistent biofilm that also included fungal hyphae, iron bacterial sheaths, diatoms, and mineral particles. HPLC analyses on Río Tinto samples showed that undegraded chl accounted for 67% of the total chl in the filamentous patches but were a minority in the brown patch (2.6%). The brown patch had a concentration of carotenoids eight times lower than that observed in the green patch. When chl concentrations were weighted for the proportion of the different patches on the streambed, undegraded chl a accounted for 89.2 mg chl a·m ^{? 2} of stream surface area (5.4 g C·m ^{? 2}). This high algal biomass was supported by relatively high nutrient concentrations and by a high phosphatase activity (V_max = 137.7 nmol methylumbelliferyl substrate·cm ^{? 2}·h ^{? 1} 1 Received 15 July 2002. Accepted 17 February 2003. , K_m = 0.0045 μM). The remarkable algal biomass in Río Tinto potentially contributed to the bacterial–fungal community and to the macroinvertebrate community and emphasizes the role that the algae may have in the organic matter cycling and energy flow in extreme systems dominated by heterotrophic microorganisms.     

Halogenating activities detected in Antarctic macroalgae

 Halogenating activities were determined in samples of 18 cultivated species of brown, red and green macroalgae from the Antarctic. Activities for the halogenating organic compounds with bromide, iodide and chloride were found. Investigated red algae (rhodophytes) showed higher brominating and iodinating activities compared to brown (phaeophytes) and green (chlorophytes) algae. The highest brominating and iodinating activities were measured in the red algae Plocamium cartilagineum (1.11±0.01 U g^-1 wet algal weight and 0.18 U g^-1 wet algal weight, respectively) and Myriogramme mangini (3.62±0.17 U g^-1 wet algal weight and 4.5 U g^-1 wet algal weight, respectively). Chlorinating activities were detected in the red alga Plocamium cartilagineum only (0.086 U g^-1 wet algal weight). Received: 12 February 1996/Accepted: 20 June 1996     

Extracellular secretion of phenolic substances from living brown algae

The chemical structures of ultraviolet (UV)- absorbing substances secreted from the healthy living brown algae, Eisenia bicyclis and Ecklonia kurome, were demonstrated. The living activity of algal cells was critically examined using a confocal laser-scanning microscope after incorporation of fluorescein diacetate (FDA) into the cells. Using thin-layer chromatography (TLC), reversed-phase three-dimensional high-performance liquid chromatography (RP-3D-HPLC) and gas chromatography-mass spectrometry (GC-MS), it was found that the UV-absorbing substances (λ_max 265–270 nm) secreted from the living brown algae mainly consisted of the three monomeric bromophenols, 2,4-dibromophenol, 2,4,6-tribromophenol and dibromo-iodophenol, but not phloroglucinol or phlorotannins. The other minor compounds detected in the secretions were as follows: benzothiazole, fatty acids (14:1, 16:0 and 18:0 acids), franesol, 3-hydroxy-2,4,4-trimethylpentyl 2-methylpropanoate and squalene. Exudation of phloroglucinol and phlorotannins was ascertained to take place only after the cell death of these algae. These results indicate that, whilst the algae are alive, polymeric phlorotannins are strictly kept within the algal body, and only monomeric bromophenols are secreted into the seawater medium.     

Coexistence,size overlap and population regulation in tidal vs. non-tidal Palaemon prawns

Summary The effect of increased habitat heterogeneity in tidal areas on coexistence between Palaemon prawns was studied at eight sites along the European Atlantic coast. Two species which are sympatric in non-tidal areas, Palaemon adspersus Rathke and P. squilla (L.) are largely allopatric in tidal areas, and the sympatric size difference decreases in allopatry. In tidal areas the smaller species, P. squilla, is restricted to brown algal belts and rockpools. A third species, P. serratus (Pennant), larger than the others, occurs under oceanic salinities in subtidal brown algal belts and there has forced P. squilla to restrict its habitat distribution to adjacent intertidal rockpools. At estuarine salinities, however, P. squilla also inhabits the brown algal belts. A larger diel variation in stomach fullness index in P. squilla than in P. adspersus persists in non-tidal areas.Abiotic factors probably restrict the two largest species, viz. P. adspersus and P. serratus, to subtidal environments; these species are sensitive to the extremes in salinity, temperature or O₂ levels characteristic of the intertidal zone. Competition and/or predation probably relegates P. squilla to the intertidal zone. In non-tidal areas, where this zone is reduced, P. squilla increases its niche width and coexists with P. adspersus, and the size differentiation associated with sympatry may reduce interspecific competition.     

ROLE OF SURFACE WOUNDS AND BROWN ALGAL EPIPHYTES IN THE COLONIZATION OF ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE) FRONDS BY VERTEBRATA LANOSA (RHODOPHYTA)1

Ascophyllum nodosum (L.) Le Jol. forms extensive beds in wave‐sheltered, rocky intertidal habitats on the northwestern Atlantic coast. This fucoid seaweed is host to an obligate red algal epiphyte, Vertebrata lanosa (L.) T. A. Chr. [=Polysiphonia lanosa (L.) Tandy], and two facultative brown algal epiphytes, Elachista fucicola (Velley) Aresch. and Pylaiella littoralis (L.) Kjellm. Although V. lanosa can occur throughout most of the length of host fronds, it largely predominates in midfrond segments. The two brown algal epiphytes are restricted to distal segments. Through field experiments conducted in Nova Scotia, Canada, we tested the hypothesis that surface wounds are required for the colonization of distal segments of host fronds by V. lanosa. Distal tissues normally have a smooth surface because of their young age (A. nodosum fronds grow apically). By creating small wounds that mimicked grazing wounds distributed elsewhere on host fronds, we demonstrated that V. lanosa can colonize distal frond segments during the growth and reproductive season (summer and autumn). Approximately half of the artificial wounds were colonized by V. lanosa during this time. The experimental exclusion of both brown algal epiphytes from distal frond segments did not affect colonization by V. lanosa. Thus, we conclude that the absence of surface irregularities on distal segments of host fronds, specifically small wounds, is the main factor explaining the absence of V. lanosa there. We propose that further experimental work clarifying epiphyte distribution in host beds will enhance our ability to understand the functional role of epiphytes in intertidal ecosystems.     

Molecular Cloning and Antiserum Development of Cyclin Box in the Brown Tide Alga Aureococcus anophagefferens

Cyclins can be useful cell cycle markers for growth rate studies on harmful algal blooms. In this study, a gene fragment corresponding to cyclin box was cloned for the brown tide alga Aureococcus anophagefferens. This algal gene fragment, designated as Btcycl1, was most similar to cyclin B. Oligopeptides based on the deduced amino acid sequence were synthesized and used to raise an antiserum that reacted on Western blots with a protein of about 63 kDa, the same size as cyclin B in other organisms. The cyclin B–like protein recognized by this antiserum, and the messenger RNA amplified using the primers, were more abundant in exponential cultures and decreased markedly in stationary cultures. This protein also appeared to be cell cycle dependent. Immunofluorescence labeling showed that this antiserum specifically stained a protein in Aureococcus cells and had no cross-reaction with bacteria that were present in the algal culture. The Btcycl1 sequence and the antiserum will provide a useful tool for studies on regulation of in situ growth rate for this brown tide alga. Received May 22, 2000; accepted July 13, 2000.     

Marine macroalgae as foods for fishes: an evaluation of potential food quality

Synopsis A revitalized view of feeding by herbivorous marine fishes is sought through two questions. First, What characteristics of major taxa of algae identify them as predictably high or low quality foods? Second, are marine algae valuable foods for fishes which do not mechanically disrupt cell walls and do not harbor specialized enzymes or microbes capable of lysing cell walls? Energy, ash and nutrient content of 16 species of marine algae were employed to assess food quality of fleshy red, green, brown and calcareous red algae. On the basis of ash, calories, total protein and total lipid content, fleshy algae should be superior to calcareous algae as foods for fishes; in addition, green algae should be superior to brown algae and brown algae superior to red algae. When the probable digestibility of storage and extracellular carbohydrates is considered, green and red algae are predicted superior to brown algae as food. Two species of damselfishes (Pomacentridae) from the Gulf of California,Eupomacentrus rectifraenum andMicrospathodon dorsalis, eat red and green algae and ignore brown and calcareous algae. They feed, therefore, in a fashion consistent with predictions based only on algal chemistry. These fishes absorb at least 20–24% of the biomass, 57–67% of the protein, 46–56% of the lipid and 37–44% of the carbohydrate contained in algae eaten in the wild. Since these damselfishes do not masticate their food, it appears that herbivorous fishes can digest major fractions of algal nutrients without mechanical destruction of algal cells.     

Food preference,food quality and diets of three herbivorous gastropods (Trochidae: Tegula) in a temperate kelp forest habitat

Summary The relationship between food preference and food quality (i.e. a food's contribution to growth and reproductive development) was examined in the laboratory for 3 species of herbivorous kelp forest gastropods (Tegula). The preference hierarchies of the 3 Tegula for 6 common algal species are the same: giant kelp (Macrocystis) is the most preferred food and brown algae are consumed at higher rates than red algae. Despite their strong preference for Macrocystis, the 3 species had significantly greater growth and/or reproductive development on a mixed-algae diet than on either brown or red algae alone. Laboratory preferences of the snails did not correspond closely with caloric content, estimated availability or quality of the algal species used in this study. However, the 3 Tegula are subject to strong benthic predation and Macrocystis provides an important spatial refuge in nature. The potential role of non-nutritional factors such as predator avoidance on the formation of food preferences is discussed.     

Latent virus‐like infections are present in a diverse range of Symbiodinium spp. (Dinophyta)

Coral reefs are increasingly threatened by disease outbreaks, which affect the coral animal and/or its algal symbionts (Symbiodinium spp.) and can cause mass mortalities. Currently around half of the recognized coral diseases have unknown causative agents. While many of the diseases are thought to be bacterial in origin, there is growing evidence that viruses may play a role. In particular, it appears that viruses may infect the algal symbionts, causing breakdown of the coral‐algal mutualism. In this study, we screened a wide range of Symbiodinium cultures in vitro for the presence of latent viral infections. Using flow cytometry and electron microscopy, we found that many types of Symbiodinium apparently harbor such infections, and that the type of putative virus varied within and among host types. Furthermore, the putative viral infections could be induced via abiotic stress and cause host cell lysis and population decline. If similar processes occur in Symbiodinium cells in hospite, they may provide an explanation for some of the diseases affecting corals and other organisms forming symbioses with these algae.     

GENOMIC INSIGHTS INTO EVOLUTIONARY RELATIONSHIPS AMONG HETEROKONT LINEAGES EMPHASIZING THE PHAEOPHYCEAE1

Heterokonts comprise a large and diverse group of organisms unified by the heterokont biflagellate condition. Monophyly of many of these lineages is well established, but evolutionary relationships among the various lineages remain elusive. Among these lineages, the brown algae (Phaeophyceae) are a monophyletic, taxonomically diverse, and ecologically critical group common to marine environments. Despite their biological and scientific importance, consensus regarding brown algal phylogeny and taxonomic relationships is missing. Our long‐term research goal is to produce a well‐resolved taxon‐rich phylogeny of the class to assess evolutionary patterns and taxonomic relationships among brown algal lineages and their relationship to other closely related heterokont groups. To accomplish this goal and augment existing loci for phaeophycean‐wide systematic studies, we generated expressed sequence tags (ESTs) from several major brown algal lineages and from the heterokont lineage representing the closest sister group to brown algae. To date, we have successfully constructed cDNA libraries for two lineages (Choristocarpus tenellus Zanardini and Schizocladia ischiensis E. C. Henry, Okuda et H. Kawai) and in the library test phase obtained up to 1,600 ESTs per organism. Annotation results showed a gene discovery rate of 45%–50% for each library revealing 500–700 unique genes from each organism. We have identified several potential genes for phylogenetic inference and used these loci for preliminary molecular clock analyses. Our molecular clock analysis suggests that the basal divergence in brown algae occurred around the time of the pennate‐centric diatom divergence. Here we report this analysis and other uses of ESTs in brown algal phylogenomics and the utility of these data for resolving the phylogeny of this group.     

Complex seasonality observed amongst diverse phytoplankton viruses in the Bay of Quinte,an embayment of Lake Ontario

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