Carbon fixation and analysis of assimilates in a coral-dinoflagellate symbiosis

Freshly collected pieces of the hermatypic coral Acropora cf. scandens containing dinoflagellate endosymbionts (presumably Gymnodinium microadriaticum) were allowed to assimilated ¹⁴C from H¹⁴CO ₃ ^- in the light and in the dark. Time-dependent carbon uptake resulted in intense ¹⁴C-labelling of ethanol-soluble as well as of insoluble assimilates. About forty ¹⁴C-labelled assimilates have been identified. Polymeric (ethanol-insoluble) compounds achieve about 30% of total radiocarbon incorporation after 60 min incubation. Kinetics of ¹⁴C-labelling of single assimilates are analyzed. Percentages of typical photosynthates in the soluble fraction undergo characteristic time-dependent changes. Lipids proved to be the main accumulation products of carbon assimilation by incorporating more than 50% of ¹⁴C after 60 min photosynthesis. The data indicate that low-molecular weight photosynthates such as ¹⁴C-glycerol and ¹⁴C-glucose are rapidly converted to constituents of the polymeric fraction(s) of the coral. Besides peptides, polysaccharides, and lipophilic substances, considerable amounts of ¹⁴C are confined to skeletal CaCO₃ of the coral. The results are discussed with respect to trophic and metabolic interrelationships between the autotrophic dinoflagellates and the A. cf. scandens tissues.     

Chemoautotrophic symbiosis in the tropical clamSolemya occidentalis (Bivalvia: Protobranchia): ultrastructural and phylogenetic analysis

Patterns of algal seasonality, and their effect on the diet and feeding preferences of the herbivorous crab Grapsus albolineatus were investigated over an 18-mo period from March 1993 to August 1994 on an exposed tropical rocky shore (Hok Tsui Peninsula at Cape d' Aguilar, Hong Kong). Algal cover was greatest in the winter months, and lowest in the summer. Foliose algae such as Ulva fasciata, Porphyra suborbiculata, and Dermonema frappieri were dominant in the winter, but died off in the summer. During the hot summer months, perennial encrusting algae e.g., Ralfsia expansa, Hildenbrandia rubra, H. occidentalis, coralline crusts and the encrusting cyanobacteria Kyrtuthrix maculans, were the dominant algal species. Seasonal variation in algal abundance influenced the dietary selectivity of the herbivorous crab G. albolineatus. In the winter, the crab fed selectively on filamentous algae (e.g. Hincksia spp., Cladophora spp., Enteromorpha spp., and the cyanobacteria Lyngbya sp.). Foliose algae (e.g. U. fasciata, P. suborbiculata, Pterocladia tenuis) formed a small part of the diet, despite being the dominant species on the shore. Foliose and filamentous algae were virtually absent from the shore in the summer, and the crabs switched to feeding solely on encrusting algae. Electivity indices revealed preferences for green and brown turf species, and avoidance of foliose algae. Faecal analysis revealed that a greater proportion of the food is digested in the winter, suggesting that G. albolineatus is able to digest filamentous algae more efficiently than encrusting algae. Feeding preferences of G. albolineatus appear to be influenced by a number of factors, including the availability, digestibility and morphology of algae. The foraging behaviour and cheliped morphology of the crab also affect food choice. The monsoonal nature of Hong Kong's climate controls the diversity and abundance of intertidal algae and, therefore, indirectly influences the diet and subsequent growth and reproductive success of the herbivorous crab G. albolineatus.     

Algal overgrowth of alcyonacean soft corals

Colonies of the soft coral Lobophytum pauciflorum (Ehrenberg, 1834) (Coelenterata: Octocorallia: Alcyonacea: Alcyoniidae), some of which were heavily overgrown by the algae Ceranium flaccidum (Kuetzing) Ardissone and Enteromorpha sp., and other minor epizoites, were collected at Taylor Reef (17°50S; 146°35E) in the Great Barrier Reef. Overgrown colonies contained the diterpene 2-epi-sarcophytoxide as the major secondary metabolite, while conspecific colonies with clean polyparies contained two diterpenes in approximately equal amounts: 14-hydroxycembra-1,3,7,11-tetraene and 15-hydroxycembra-1,3,7,11-tetraene. By contrast, twenty conspecific pairs of overgrown and clean colonies of other alcyoniid soft corals collected from Pelorus Channel, Palm Island Group (18°34S; 146°29E), showed no chemical differences within in the pairs. Cultures of a common species of Ceramium [C. codii (Richards) Mazoyer] were incubated with different concentrations of nine soft-coral-derived diterpenes and significant algal growth inhibition was observed in many cases. It appears that terpenoids from soft coral may contribute to the lack of epizoic organisms on soft-coral polyparies.     

Algal purification of pretreated landfill Leachate

The efficiency of microalgae in removing various pollutants in landfill leachate after pretreatment by free stripping or air stripping was tested by a laboratory batch system. The results showed that Chlorella pyrenoidosa and Scenedesmus sp. had similar removal efficiencies with regard to ammoniacal‐nitrogen, oxidized‐nitrogen, orthophosphate and chemical oxygen demand (COD). The COD removal by algal treatment was better in Junk Bay (JB) leachate than in Gin Drinkers’ Bay (GDB) leachate (14–21% and 0.4–7% respectively). No significant difference (P > 0.05) was found in removing other nutrients including ammoniacal‐nitrogen, oxidized‐nitrogen and orthophosphate between leachate from the two landfills, regardless of the pretreatment used. The removal efficiencies of ammoniacal‐nitrogen and phosphorus were found to be higher in air‐stripped leachate than in free‐stripped one. Removal of ammoniacal‐nitrogen and phosphorus in air‐stripped leachate was 30% and 87% respectively. Poor removal of ammoniacal‐nitrogen was probably due to a deficiency in phosphorus (high N : P ratio) for algal growth in leachate. The two‐stage leachate treatment (ammonia stripping followed by algal purification) resulted in overall reduction of COD (38–51%), ammoniacal‐nitrogen (72–96%) and orthophosphate (79–96%).     

Bacterial symbiosis in Northeast Pacific Vestimentifera: a TEM study

A number of new vestimentiferan species occur at northeast Pacific hydrothermal vent sites. The trophosome and bacterial symbionts of three species, collected from the Juan de Fuca and Explorer Ridges between 1984 and 1986, were studied by transmission electron microscopy (TEM). As in Riftia pachyptila, trophosome tissue is organised into lobules each having an axial blood vessel, and intracellular bacterial symbionts are contained in membrane vacuoles. The bacteria have many cytoplasmic inclusions including tubular membrane systems, glycogen-like particles and poly--hydroxybutyrate (PHB) or sulfur bodies. Glycogen production may be quantitatively important to both the symbionts and the host. Glycogen-like granules appear to first accumulate in the bacterial cells and then be released into the bacteriocyte cytoplasm as bacteria are degraded. Although various stages of bacterial growth and degradation are observed, data are insufficient to verify any across-lobule progression of these processes. Morphological comparison of the symbionts reveals that similar symbionts are found in different vestimentiferan species and that one to two bacterial types exist within single individuals. Two possible models of trophosome function and nutrient exchange are discussed.Deceased     

Role of standard incidence in an eco-epidemiological system: A mathematical study

Ecology and epidemiology are two major fields of study in their own right, but they have some common features. [Chattopadhyay, J., Pal, S., El Abdllaoui, A., 2003. Classical predator–prey system with infection of prey population—a mathematical model. Math. Meth. Appl. Sci. 26, 1211–1222] considered a predator–prey model with disease in the prey population. They analyzed the system based on the assumption that horizontal incidence follows simple mass action incidence. Mass action incidence is appropriate for a constant population, but for a large population, standard incidence is more appropriate. The complicated dynamics around (0, 0, 0) arise because of standard incidence. The conditions under which the population reaches the origin either by following the axis or in a spiral pattern were determined. Numerical experiments were performed to observe the dynamics of the system with mass action incidence and standard incidence. This investigation showed that the infection rate plays a crucial role for predicting the behavior of the dynamics in the long run.     

A new bathymodioline mussel symbiosis at the Juan de Fuca hydrothermal vents

Until recently, the only major hydrothermal vent biogeographic province not known to include bathymodioline mussels was the spreading centers of the northeast Pacific, but deep-sea dives using DSV Alvin on the Endeavor segment of the Juan de Fuca Ridge (47°56N 129°06W; ∼2,200 m depth) in August 1999 yielded the only recorded bathymodioline mytilids from these northeastern Pacific vents. One specimen in good condition was evaluated for its relatedness to other deep-sea bathymodioline mussels and for the occurrence of chemoautotrophic and/or methanotrophic symbionts in the gills. Phylogenetic analyses of the host cytochrome oxidase I gene show this mussel shares evolutionary alliances with hydrothermal vent and cold seep mussels from the genus Bathymodiolus, and is distinct from other known species of deep-sea bathymodiolines, suggesting this mussel is a newly discovered species. Ultrastructural analyses of gill tissue revealed the presence of coccoid bacteria that lacked the intracellular membranes observed in methanotrophic symbionts. The bacteria may be extracellular but poor condition of the fixed tissue complicated conclusions regarding symbiont location. A single gamma-proteobacterial 16S rRNA sequence was amplified from gill tissue and directly sequenced from gill tissue. This sequence clusters with other mussel chemoautotrophic symbiont 16S rRNA sequences, which suggests a chemoautotrophic, rather than methanotrophic, symbiosis in this mussel. Stable carbon (δ¹³C = −26.6%) and nitrogen (δ¹⁵N = +5.19%) isotope ratios were also consistent with those reported for other chemoautotroph-mussel symbioses. Despite the apparent rarity of these mussels at the Juan de Fuca vent sites, this finding extends the range of the bathymodioline mussels to all hydrothermal vent biogeographic provinces studied to date.     

Algal biomass valorization for biofuel production and carbon sequestration: a review

The world is experiencing an energy crisis and environmental issues due to the depletion of fossil fuels and the continuous increase in carbon dioxide concentrations. Microalgal biofuels are produced using sunlight, water, and simple salt minerals. Their high growth rate, photosynthesis, and carbon dioxide sequestration capacity make them one of the most important biorefinery platforms. Furthermore, microalgae's ability to alter their metabolism in response to environmental stresses to produce relatively high levels of high-value compounds makes them a promising alternative to fossil fuels. As a result, microalgae can significantly contribute to long-term solutions to critical global issues such as the energy crisis and climate change. The environmental benefits of algal biofuel have been demonstrated by significant reductions in carbon dioxide, nitrogen oxide, and sulfur oxide emissions. Microalgae-derived biomass has the potential to generate a wide range of commercially important high-value compounds, novel materials, and feedstock for a variety of industries, including cosmetics, food, and feed. This review evaluates the potential of using microalgal biomass to produce a variety of bioenergy carriers, including biodiesel from stored lipids, alcohols from reserved carbohydrate fermentation, and hydrogen, syngas, methane, biochar and bio-oils via anaerobic digestion, pyrolysis, and gasification. Furthermore, the potential use of microalgal biomass in carbon sequestration routes as an atmospheric carbon removal approach is being evaluated. The cost of algal biofuel production is primarily determined by culturing (77%), harvesting (12%), and lipid extraction (7.9%). As a result, the choice of microalgal species and cultivation mode (autotrophic, heterotrophic, and mixotrophic) are important factors in controlling biomass and bioenergy production, as well as fuel properties. The simultaneous production of microalgal biomass in agricultural, municipal, or industrial wastewater is a low-cost option that could significantly reduce economic and environmental costs while also providing a valuable remediation service. Microalgae have also been proposed as a viable candidate for carbon dioxide capture from the atmosphere or an industrial point source. Microalgae can sequester 1.3 kg of carbon dioxide to produce 1 kg of biomass. Using potent microalgal strains in efficient design bioreactors for carbon dioxide sequestration is thus a challenge. Microalgae can theoretically use up to 9% of light energy to capture and convert 513 tons of carbon dioxide into 280 tons of dry biomass per hectare per year in open and closed cultures. Using an integrated microalgal bio-refinery to recover high-value-added products could reduce waste and create efficient biomass processing into bioenergy. To design an efficient atmospheric carbon removal system, algal biomass cultivation should be coupled with thermochemical technologies, such as pyrolysis.

     

Algal succession in a Macrocystis pyrifera forest

Algal succession within a subtidal forest of the giant kelp Macrocystis pyrifera was studied by following colonization and community development on concrete blocks fastened to the bottom. Sets of blocks were placed in the bed at 3-month intervals. Subsequent algal development on each set was followed for over a year. All macroscopic species attached to the substrata were noted, and the number and lenght of basal branches determined every 1 to 3 months. Colonizing plants fell into 3 categories: rapid-growing ephemerals, and rapid and slow-growing perennials. Ephemerals such as Giffordia (Ectocarpus) mitchellae, Colpomenia peregrina, and diatom films generally produced and initial bloom on the blocks but were gradually replaced by perennials (articulated corallines, Rhodymenia spp., Gigartina spp.) characteristic of the mature kelp community. These stages, rather than representing “ecological” succession, seemed to reflect differences in growth rate and success in interspecific competition for space and light. Colonization on the blocks varied with season, indicating that most species have either a spring-summer or fall-winter period of maximum reproduction. M. pyrifera sporophyte colonization was greatest in spring. During community development, algal diversity (H), number of species (s) and evenness (J) all reached a peak within 100 to 200 days regardless of the time the blocks were started. Diversity and number of species then fell as ephemeral species disappeared. These species were apparently unable to compete with perennials and, once gone, did not recolonize. Evenness remained high.     

Symbiosis within a symbiosis: Intracellular bacteria within the endosymbiotic protistNephromyces

The marine protistNephromyces Giard, 1888 is a chronic endosymbiont of molgulid tunicates. Ultrastructural and cytochemical studies of this protist, isolated from molgulid hosts collected from the Pacific, Atlantic and Gulf Coasts of the United States, indicate thatNephromyces is itself chronically infected with Gramnegative, intracellular bacteria. Molgulid tunicates are thus the locus of a nested,tripartite endosymbiosis. Intracellular bacteria are present in both trophic and reproductive stages ofNephromyces, suggesting that the bacterial-Nephromyces symbiosis is an hereditary association. The presence of endosymbionts inNephromyces raises the possibility that some ofNephromyces' metabolic characteristics, in particular its high urate oxidase activity, might be supplied not byNephromyces itself, but rather by its intracellular bacteria, possibly functioning as peroxisomal analogues.     

A mathematical model of PCB bioaccumulation in plankton

In batch experiments exposing individual plankton constituents to Aroclor 1254 PCB, the rate at which the organism approaches partitioning equilibrium appears to be partly size-dependent while the extent of PCB accumulation is species-specific. The sorptive desorptive kinetics of PCB in these experiments can be described mathematically by a first-order expression. Employing this expression in a model plankton food web permits examination of the role of feeding and sorptive processes in determining PCB body burden under various environmental conditions. When ingestion rates exceed desorption and excretion rates, a consuming organism accumulates PCB above levels predicted by equilibrium partitioning relationships. Feeding-induced oscillations in PCB body burden could thus obscure the reduction of soluble PCB concentration which determine a “baseline” PCB body burden. Unless referenced to a specific set of biological and environmental conditions, the importance of direct partitioning from water vs. food uptake appears to be a moot topic.     

A reevaluation of the role of glycerol in carbon translocation in zooxanthellae-coelenterate symbiosis

Glycerol has been traditionally viewed as the main form of carbon translocated from zooxanthellae to the coelenterate host. Most of this glycerol was postulated to be used by the coelenterate host for lipid synthesis. Recent work suggests that large amounts of photosynthetically fixed carbon is synthesized into lipid in the algae, and then translocated as lipid droplets to the host. These two hypotheses of carbon translocation are not mutually exclusive, but to reconcile them the role of glycerol must be reevaluated. In this study the short term metabolic fate of uniformly labelled ¹⁴C-glycerol, ¹⁴C-bicarbonate, and ¹⁴C-acetate was examined in zooxanthellae and coelenterate host tissue isolated from Condylactis gigantea tentacles. When host and algal triglycerides, synthesized during 90-min light and dark incubations in ¹⁴C-bicarbonate and ¹⁴C-acetate, were deacylated, more than 80% of the activity was found in the fatty acid moiety. In contrast, triglycerides isolated from zooxanthellae and coelenterate host tissue incubated in ¹⁴C-glycerol in the dark for 90 min were found to have more than 95% of their radioactivity in the glycerol moiety. During the 90-min ¹⁴C-glycerol incubations in the light, the percentage of radioactivity in the fatty acid moiety of zooxanthellae triglycerides increased to 37%. The percentage of radioactivity in the host tissue triglycerides fatty acid moiety stayed below 5% during the 90-min ¹⁴C-glycerol incubations in the light. These results show that neither the zooxanthellae nor the host can rapidly convert glycerol to fatty acid. Radioactivity from ¹⁴C-glycerol, which does eventually appear in host lipid, may have been respired to ¹⁴CO₂, then photosynthetically fixed by the zooxanthellae and synthesized into lipid fatty acid.     

Phosphate acquisition in the giant clam-zooxanthellae symbiosis

The effect of phosphate on the giant clam Tridacna gigas and on its symbiotic dinoflagellate Symbiodinium sp. was compared with that on cultured Symbiodinium sp. originally isolated from the same clarn species. Incubation of whole clams in elevated phosphate (10 M) reduced their capacity for phosphate uptake, but the uptake capacity of the clam's zooxanthellae population was not influenced. In addition, there was no change in the zooxanthellae density and the N:P ratio, of these algae., On the other hand, cultured zooxanthellae were influenced by the phosphate regimen of their culture medium. Compared with controls (0 M P), addition of 10 M phosphate to the culture medium caused an increase of 100% in cell density and decreases of 50% in the N:P ratio, and 80% in the phosphate-uptake capacity of the zooxanthellae. Zooxanthellae freshly isolated from the clams exhibited properties similar to those of zooxanthellae cultured in the absence of phosphate. These results demonstrate that the zooxanthellae population of T. gigas have limited access to the inorganic phosphate in sea water and the phosphate reserves within the animal host.     

海洋藻类病毒与赤潮防治

病毒是海洋中丰度最高的生物,全球海洋中大约有1030个病毒,海洋病毒的宿主包括从细菌到大型海洋生物等几乎所有的海洋生物.海洋病毒在调控种群结构及生物地球化学循环中起着至关重要的作用,并且,病毒可以通过水平基因转移来操控宿主的代谢活动.藻类病毒能够通过裂解藻类从而起到控制赤潮的作用.随着藻类病毒研究的不断发展,人们已经分离到大量的藻类病毒,包括双链或单链的DNA病毒及RNA病毒,其分布于细胞质或细胞核中.本文简要概述了海洋病毒研究方面的发展现状,及海洋病毒在生态环境中的重要作用.集中综述了藻类病毒(包括原核藻类病毒和真核藻类病毒)的研究进展,讨论了海洋藻类病毒与赤潮生物的关系.介绍了藻类病毒在赤潮控制方面所取得的一些成果,展望了藻类病毒调控赤潮的前景.我国在藻类病毒方面的探索研究还只是刚刚起步,研究藻类病毒的前景十分广阔.     

Mutualistic stability in the arbuscular mycorrhizal symbiosis: exploring hypotheses of evolutionary cooperation

The 450-million-year-old symbiosis between the majority of land plants and arbuscular mycorrhizal fungi (AMF) is one of the most ancient, abundant, and ecologically important mutualisms on Earth. Yet, the evolutionary stability of mycorrhizal associations is still poorly understood, as it follows none of the constraints thought to stabilize cooperation in other well-known mutualisms. The capacity of both host and symbiont to simultaneously interact with several partners introduces a unique dilemma; detecting and punishing those exploiting the mutualism becomes increasingly difficult if these individuals can continue to access resources from alternative sources. Here, we explore four hypotheses to explain evolutionary cooperation in the arbuscular mycorrhizal symbiosis: (1) pseudo-vertical transmission and spatial structuring of plant and fungal populations leading to local adaptation of partners; (2) luxury resource exchange in which plants trade surplus carbon for excess fungal nutrients; (3) partner choice allowing partners to associate with better cooperators; and (4) host and symbiont sanctions which actively reward good partners and punish less cooperative ones. We propose that mycorrhizal cooperation is promoted by an exchange of surplus resources between partners and enforced through sanctions by one or both partners. These mechanisms may allow plant and fungal genotypes to discriminate against individuals employing exploitative strategies, promoting patterns of partner choice. Together these selection pressures provide a framework for understanding the stabilization of mycorrhizal cooperation over evolutionary time.     

Forest succession suppressed by an introduced plant-fungal symbiosis

Microbial symbionts can affect plant nutrition, defensive chemistry, and biodiversity. Here we test the hypothesis that symbionts alter the speed and direction of plant succession in communities that are shifting from grasslands to forests. A widespread C3 grass introduced to the United States, Lolium arundinaceum (tall fescue), hosts a fungal endophyte that is toxic to herbivores. In replicated experimental grasslands, the presence of the endophyte in tall fescue reduced tree abundance and size, altered tree composition, and slowed plant species turnover. In addition, consumption of tree seedlings by voles (Microtus spp.) was 65% higher in plots with the endophyte at the one grassland site where these data were collected. Despite its negligible contribution to community biomass, a microbial symbiont suppressed tree establishment, posing an important constraint on the natural transition from grasslands to forests.     

Context-dependent effects of symbiosis: Zoanthidea colonization generally improves Demospongiae condition in native habitats

In order to reconcile existing data and hypotheses on the relationship outcomes of Caribbean Zoanthidea-Demospongiae symbioses, the context-dependent survival and growth (metrics of host sponge condition) were monitored for 8–12?months, with and without Zoanthidean symbionts, in native (coral reef) and novel (mangrove) habitats. Experiments repeated over space and time revealed significant positive effects of Zoanthidea colonization on metrics of host condition and indicated that the outcome of these symbioses can shift from mutualism to parasitism when transplanted to novel habitats. Although the precise mechanisms of the symbioses remain obscured and most of the species associations have not been examined, these experiments demonstrate an example where relationship outcomes are more conserved across their evolutionary history than host associations.     

Nutrient-limited toxin production and the dynamics of two phytoplankton in culture media: A mathematical model

In this paper we have proposed and analyzed a simple mathematical model consisting of four variables, viz., nutrient concentration, toxin producing phytoplankton (TPP), non-toxic phytoplankton (NTP), and toxin concentration. Limitation in the concentration of the extracellular nutrient has been incorporated as an environmental stress condition for the plankton population, and the liberation of toxic chemicals has been described by a monotonic function of extracellular nutrient. The model is analyzed and simulated to reproduce the experimental findings of Graneli and Johansson [Graneli, E., Johansson, N., 2003. Increase in the production of allelopathic Prymnesium parvum cells grown under N- or P-deficient conditions. Harmful Algae 2, 135–145]. The robustness of the numerical experiments are tested by a formal parameter sensitivity analysis. As the first theoretical model consistent with the experiment of Graneli and Johansson (2003), our results demonstrate that, when nutrient-deficient conditions are favorable for the TPP population to release toxic chemicals, the TPP species control the bloom of other phytoplankton species which are non-toxic. Consistent with the observations made by Graneli and Johansson (2003), our model overcomes the limitation of not incorporating the effect of nutrient-limited toxic production in several other models developed on plankton dynamics.