UNCOUPLING OF VARIOUS MEASURES OF GROWTH IN ULVA ROTUXDATA(CHLOROPHYTA) FOLLOWING A LARGE DECREASE IN IRRADIANCE1

A vegetative clone of the chlorophyte macroalga Ulva rotundata Blid. was maintained in an outdoor continuous flow system and subjected to a large decrease in irradiance. Specific growth rates based on changes in fresh (μ_FW) and dry weight (μ_DW) and surface area (μ_SA) were determined using precut disks over the 24 h following a post-sunset transfer from full sunlight (100% I₀) to 9% I₀ All three measures of growth rate were approximately equivalent for untransferred control plants at either limiting (9%) or saturating (100%)I₀. Transferred disks exhibited μ_FW and μ_SA which were slightly lower than 100%I₀ controls and much higher than 9% I₀ controls; μ_DW was nearly identical for transferred disks and 9% I₀ controls. Cell size was unchanged following transfer, indicating that surface area changes reflected a proportional increase in cell number. Cell division therefore continued at a high rate for one day following transfer of U. rotundata to irradiances which are subsaturating for photosynthesis (indicated by μ_Dw). Starch reserves were largely depleted, and the C/N ratio decreased during this period.     

Improvement of lipid profile and antioxidant of hypercholesterolemic albino rats by polysaccharides extracted from the green alga Ulva lactuca Linnaeus

Sulfated polysaccharides from Ulva lactuca were extracted in hot water and precipitated by ethanol then orally gavaged to rats fed on a hypercholesterolemic diet for 21 days to evaluate the antihypercholesterolemic and antioxidant actions. Atorvastatine Ca (Lipitor) was used as a reference drug. The intragastric administration of U. lactuca extract to hypercholesterolemic rats caused significant decrease of serum total lipids, triglycerides, total cholesterol, LDL-cholesterol and vLDL-cholesterol levels. Whereas, HDL-cholesterol concentration was markedly increased by 180%. Aqueous extract showed a significant ameliorative action on elevated atherogenic index, creatine kinase and lactate dehydrogenase activities of hypercholesterolemic group. Furthermore, serum activities of transaminases and alkaline phosphatase were also improved. High fat diet intake caused a highly significantly elevated serum urea, creatinine concentration. These effects were reversed by oral administration of U. lactuca extract. Sulfates polysaccharides extract of U. lactuca ameliorate hepatic enzymatic (catalase, glutathione peroxidase and superoxide dismutase), non-enzymatic (reduced glutathione & total thiol) antioxidant defenses and thiobarbituric acid reactive substances. In conclusion, the tested U. lactuca polysaccharides extract has potent hypocholesterolemic and antioxidant effects in experimentally-induced hypercholesterolemic animal model.     

SEASONAL VARIABILITY OF PHYSICOCHEMICAL AND RHEOLOGICAL PROPERTIES OF ULVAN IN TWO ULVA SPECIES (CHLOROPHYTA) FROM THE BRITTANY COAST1

The seasonal variability in the extraction yield, physicochemical characteristics, and rheological properties of ulvan from two Ulva species contributing to Brittany “green tides” has been studied. These seaweeds were collected in the water column for Ulva armoricana Dion, de Reviers et Coat and on hard substrata for Ulva rotundata Bliding. The maximum ulvan extraction efficiency was not related to the maximum ulvan content in the seaweeds, but with the active growth period of the seaweeds. Ulvan chemical structure, macromolecular characteristics, and rheological properties were affected by both species and seasons. The proportion of high‐molecular‐weight ulvan was the major factor positively correlated with the gelling properties. Characteristics of ulvan from U. rotundata subjected to tides were more affected by seasons than ulvan from U. armoricana living in a more constant environment. These results point to several useful recommendations concerning Ulva sp. biomass collected with regard to ulvan characteristics and uses.     

Antimicrobial activity observed among cultured marine epiphytic bacteria reflects their potential as a source of new drugs

The surfaces of marine eukaryotes provide a unique habitat for colonizing microorganisms where competition between members of these communities and chemically mediated interactions with their host are thought to influence both microbial diversity and function. For example, it is believed that marine eukaryotes may use their surface-associated bacteria to produce bioactive compounds in defence against competition and to protect the host against further colonization. With the increasing need for novel drug discovery, marine epibiotic bacteria may thus represent a largely underexplored source of new antimicrobial compounds. In the current study, 325 bacterial isolates were obtained from the surfaces of marine algae Delisea pulchra and Ulva australis . Thirty-nine showed to have antimicrobial activity and were identified via 16S rRNA gene sequencing. The majority of those isolates belonged to Alpha- and Gammaproteobacteria . Interestingly, the most commonly isolated bacterial strain, Microbulbifer sp., from the surface of D. pulchra has previously been described as an ecologically significant epibiont of different marine eukaryotes. Other antimicrobial isolates obtained in this study belonged to the phyla Actinobacteria , Firmicutes and Bacteroidetes . Phylogenetically, little overlap was observed among the bacteria obtained from surfaces of D. pulchra and U. australis . The high abundance of cultured isolates that produce antimicrobials suggest that culturing remains a powerful resource for exploring novel bioactives of bacterial origin.     

Growth and Thallus Morphogenesis of Ulva mutabilis (Chlorophyta) Depends on A Combination of Two Bacterial Species Excreting Regulatory Factors

Axenic Ulva mutabilis gametes develop parthenogenetically into callus‐like colonies consisting of undifferentiated cells without normal cell walls. From the accompanying microbial flora of established laboratory strains of U. mutabilis with normal morphology, a Roseobacter, a Sulfitobacter, and a Halomonas species were isolated. Each of these microbe species alone induced the development of the Ulva gametes into thalli composed of differentiated cells with characteristic deficiencies. Typical traits of these thalli were: an enhanced rate of cell division not followed by cell expansion, the presence of unusual cell wall protrusions, and the absence of differentiated rhizoid cells. The addition of a Cytophaga species, also derived from the same microbial flora, to either one of the three other strains resulted in the development of normal fast growing thalli with the typical morphology of the algal strain used. These effects are mediated by specific regulatory factors that are excreted into the environment by the bacteria and could be also isolated from the bacterial cell extracts. In contrast with the Cytophaga‐factor, the regulatory factor of the three other bacterial species was also found intracellularly in other bacterial strains not associated with Ulva, but in this case it was not excreted. Functionally, the Roseobacter‐, Sulfitobacter‐, and Halomonas‐factors resemble a cytokinin, while the Cytophaga‐factor acts similar to auxin. Neither factor could be replaced by known phytohormones. The Roseobacter species exhibits a specific chemotactic affinity to the rhizoid cells of U. mutabilis and seems to cooperate with the Cytophaga strain and the alga by chemical communication forming a symbiotic tripartite community.     

Bioaccumulation of alkaline soil metals (Ca,Mg) and heavy metals (Cd,Ni, Pb) patterns expressed by freshwater species of Ulva (Wielkopolska,Poland)

The paper includes results of the first study on the accumulation of selected metals in freshwater populations of Ulva taxa at 16 sites in Poland. The thalli examined contained very high concentrations of Ca and Mg, owing to well‐developed surface incrustations of carbonate. Among the heavy metals investigated, the most significant concentration in the thalli was Ni, whereas the lowest was Pb. The median concentrations of Ni and Cd in the freshwater Ulva thalli were significantly higher than those reported in the available literature for marine taxa of the same genus. Several statistically significant correlations were found when the concentrations of different metals in the thalli and the water were analysed (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Biosorption of mercury from aqueous solution by Ulva lactuca biomass

The mercury biosorption onto non-living protonated biomass of Ulva lactuca, as an alternative method for mercury removal from aqueous solutions, was investigated. Batch equilibrium tests showed that at pH 3.5, 5.5 and 7 the maxima of mercury uptake values, according to Langmuir adsorption isotherm, were 27.24, 84.74 and 149.25 mg/g, respectively. The ability of Ulva lactuca biomass to adsorb mercury in fixed-bed column, was investigated as well. The influence of column bed height, flow rate and effluent initial concentration of metal was studied. The adsorbed metal ions were easily desorbed from the algal biomass with 0.3 N H₂SO₄ solution. After acid desorption and regeneration with distilled water, the biomass could be reused for other biosorption assays with similar performances.     

Changes in Thallus Weight and Size in the Green Alga Ulva fenestrata under Artificial Conditions

From August to October 2002, daily measurements of the thallus weight and area were taken in sporophytes and male and female gametophytes of Ulva fenestrata at similar developmental phases. The algae were reared in aquaria at a constant temperature (22 ± 0.5°C); illumination was applied for 12h a day at a photosynthetically active radiation intensity of 400 E/(m² s). All generations showed a linear increase in the thallus weight and area over time with the same relative daily increment (8 to 15%). Generations differed significantly in time to onset of sporogenesis or gametogenesis. The female gametophyte, sporophyte, and male gametophyte began to release gametes or spores in 7, 10, and 15 days, respectively. A scheme for the distribution of cells among age groups is proposed. The scheme seems to account for the linear pattern of thallus growth.     

Carbonate ions appear to neither inhibit nor stimulate use of bicarbonate ions in photosynthesis by Ulva lactuca

Rates of photosynthesis by the marine macroalga Ulva lactuca were measured in a factorial experiment at five concentrations of HCO₃^? and CO₃^2- between 0·20 and 1·26 mol m^?3, but very low concentrations of CO₂. The results demonstrated that HCO₃^? was available for use, but an analysis of variance showed that CO₃^2- had neither an inhibiting nor a stimulating effect on rates of photosynthesis over this concentration range. Over the experiment, pH varied from 8·46 to 10·06 and this also had no significant effect on rates of photosynthesis. The lack of a stimulatory effect of high concentrations of CO₃^2- on the rate of photosynthesis at low concentrations of HCO₃^? was taken as circumstantial evidence for direct uptake of HCO₃^? rather than proton extrusion and external production of CO₂. In the rockpools in which U. lactuca grows, pH values up to 10·35 have been recorded, and for much of the time, CO₃^2- was the major form of inorganic carbon available. The apparent lack of an ability to use CO₃^2- under these conditions suggests that direct use of CO₃^2- as a source of inorganic carbon for photosynthesis is unlikely to be widespread.