Ultrastructure of ulvan: A polysaccharide from green seaweeds

Ultrastructural analysis of the gel forming green seaweed sulfated polysaccharide ulvan revealed a spherical‐based morphology (10–18 nm diameter) more or less aggregated in aqueous solution. At pH 13 in TBAOH (tetrabutyl ammonium hydroxyde) or NaOH, ulvan formed an open gel‐like structure or a continuous film by fusion or coalescence of bead‐like structures, while in acidic pH conditions, ulvan appeared as dispersed beads. Low concentrations of sodium chloride, copper or boric acid induced the formation of aggregates. These results highlight the hydrophobic and aggregative behavior of ulvan that are discussed in regard to the peculiar gel formation and the low intrinsic viscosity of the polysaccharide in aqueous solution. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 652–664, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Characterization of an Alteromonas long-type ulvan lyase involved in the degradation of ulvan extracted from Ulva ohnoi

Ulvan is a sulfated polysaccharide found in the cell wall of the green algae Ulva. We first isolated several ulvan-utilizing Alteromonas sp. from the feces of small marine animals. The strain with the highest ulvan-degrading activity, KUL17, was analyzed further. We identified a 55-kDa ulvan-degrading protein secreted by this strain and cloned the gene encoding for it. The deduced amino acid sequence indicated that the enzyme belongs to polysaccharide lyase family 24 and thus the protein was named ulvan lyase. The predicted molecular mass of this enzyme is 110 kDa, which is different from that of the identified protein. By deletion analysis, the catalytic domain was proven to be located on the N-terminal half of the protein. KUL17 contains two ulvan lyases, one long and one short, but the secreted and cleaved long ulvan lyase was demonstrated to be the major enzyme for ulvan degradation.     

Structure and functional properties of ulvan, a polysaccharide from green seaweeds

With today's interest in novel renewable chemicals and polymers, the underexploited marine green algae belonging to species of Ulva and Entermorpha stimulated interest as sources of polysaccharides with innovative structure and functional properties. These algae are common on all seashores and can produce in time an important amount of biomass in nutrient-enriched waters. The major water-soluble polysaccharide, ulvan, extracted from the cell wall represents about 8-29% of the algae dry weight. The original physicochemical, rheological, and biological properties recently unraveled for this complex sulfated aldobiouronan open the way for novel potential applications.     

从藻类生理生态学角度解析绿潮爆发的内在机制

绿潮是在特殊环境条件下,海水中某些大型绿藻爆发性增殖或高度聚集而引发的海洋生态异常现象。自2007年起,黄海已连续15年爆发绿潮,对沿岸生态环境、社会发展、经济建设造成极其严重的危害,解决绿潮问题刻不容缓。绿潮的形成是外因和内因综合作用的结果。目前,国内外学者对绿潮爆发的外因,即环境因子已具有科学的认知,并围绕绿潮藻类对某些环境因子的生理响应展开系列研究,且取得了一定成果。然而,针对绿潮爆发的内因,即绿潮藻类为应对大幅波动的环境因子而产生的极强的生理生态适应性尚未进行深入探讨。本文从藻类生理生态学角度入手,综述绿潮成因种对多种生态因子波动的响应机制,包括光照强度、二氧化碳、温度、盐度与干出、营养盐、重金属及生物因素,归纳了绿潮藻类的光合生长生理、营养生理和繁殖生理对环境因子波动的适应性调节机制,揭示了绿潮藻类爆发的内因。     

The effect of parathion on green algae

Summary Uptake of the pesticide parathion from aqueous solution by uni-cellular green algae has been investigated. The removal of parathion from solution by Chlorococcales does not occur through passive or by active permeation into the cells but by adsorption, which can be described by the. Freundlich-adsorption-isotherm equation. Investigations of partially purified cell walls phow that neither mucus, cellulose walls nor plasmamembranes adsorb parathion. The lipid containing trilaminar sheath (TLS) adsorbs the pesticide. The relevance of these results to ecological problems is discussed.     

Some effects of 2537 A on green algae and chloroplast preparations

1. The kinetics of the inactivation of photosynthesis by 2537 A in Chlorella pyrenoidosa and Scenedesmus D(1) indicate that, while the destruction process is largely a first order effect, higher order effects also occur, which become evident at low exposures. In agreement with previous observations, endogenous respiration is insensitive to exposures which inactivate photosynthesis. 2. In Scenedesmus D(1) a solid dose of ultraviolet has no more effect on the photosynthetic apparatus than a dose of equal total duration interrupted by periods of photosynthesis. Nor is any difference noted if the cells are in a different buffer, e.g. 0.05 M KH(2)PO(4), or carbonate-bicarbonate buffer 9. 3. In C. pyrenoidosa, a solid dose and an interrupted dose cause equal effects on photosynthesis when neutral phosphate buffer is used. If the ultraviolet exposure schedules are identical, equal effects are also noted in cells suspended in buffer 9, and in 0.05 M phosphate (pH 6.2). Solid exposures are, however, much more effective than interrupted exposures, when buffer 9 is used. 4. Oxygen evolution (Hill reaction), photosynthesis, and photoreduction in Scenedesmus D(1) are equally sensitive to a given dose of ultraviolet. The mechanism responsible for adaptation to hydrogen metabolism is not more sensitive to ultraviolet than is the photosynthetic mechanism. The O(2)/H(2)/CO(2) reaction in darkness is less sensitive to ultraviolet than any of the above reactions. 5. Glucose oxidation by C. pyrenoidosa, and colony formation in Scenedesmus D(1) are far more sensitive to a given dose of ultraviolet than photosynthesis in these organisms. 6. The photosynthetic apparatus of C. pyrenoidosa is more sensitive to ultraviolet than that of Scenedesmus D(1). 7. The Hill reaction in chloroplast fragments is also inactivated by 2537 A by a first order process. Exposures which inactivate this reaction completely have no effect on polyphenol oxidase, cytochrome oxidase, or catalase in the same chloroplast preparation. 8. After irradiation, the survival of photosynthesis in Scenedesmus D(1) and of the Hill reaction in chloroplast fragments are independent of the light intensity used to measure these processes. 9. No significant changes occur in the ultraviolet absorption of chloroplasts after an exposure to 2537 A, which completely inactivates the Hill reaction.     

Fatty acids filamentous green algae

Fatty acid analyses of several filamentous green algae were conducted using gas-liquid chromatography. Two bryophytes were also examined. Qualitatively, the genera of algae studied were divided into two groups: (A) algae that have significant amounts of polyunsaturated C₂₀ fatty acids and (B) algae that lack or only have very small amounts of the C₂₀ acids. On the basis of fatty acid content, the algae of Group A more closely resemble the bryophytes than do the algae of Group B. Culture age was shown to cause quantitative but not qualitative variations in fatty acid content. It is evident from this study that extrapolation to land plants, from studies on the fatty acid content of the green algae, should include the filamentous forms.     

Glycolate pathway in green algae

By three criteria, the glycolate pathway of metabolism is present in unicellular green algae. Exogenous glycolate-1-¹⁴C was assimilated and metabolized to glycine-1-¹⁴C and serine-1-¹⁴C. During photosynthetic ¹⁴CO₂ fixation the distributions of ¹⁴C in glycolate and glycine were similar enough to suggest a product-precursor relationship. Five enzymes associated with the glycolate pathway were present in algae grown on air. These were P-glycolate phosphatase, glycolate dehydrogenase (glycolate:dichloroindophenol oxidoreductase), l-glutamate:glyoxylate aminotransferase, serine hydroxymethylase, and glycerate dehydrogenase. Properties of glycerate dehydrogenase and the aminotransferase were similar to those from leaf peroxisomes. The specific activity of glycolate dehydrogenase and serine hydroxymethylase in algae was 1/5 to 1/10 that of the other enzymes, and both these enzymes appear ratelimiting for the glycolate pathway.     

Glycolate metabolism in green algae

Using ¹⁴C-labelled substrates, the succession of the single steps in the glycolate metabolism was investigated in Mougeotia scalaris and Eremosphaera viridis , which, within the group of green algae, are representatives of the evolutionary lines of Charophyta and Chlorophyta , respectively. In both algae the same metabolites are formed as in higher plants, although in Eremosphaera , which in contrast to Mougeotia does not possess leaf peroxisomes, all reactions are exclusively mitochondrial. Concomitant with the oxidation of glycolate, the synthesis of ATP was demonstrated in Eremosphaera . Formation of tartronic semi-aldehyde or other products different from those in land plants could not be demonstrated in either of these algae. Excretion of glycolate by Mougeotia and Eremosphaera is enhanced by decreasing the CO₂ concentration as well as by increasing the light intensity, but is completely stopped about 14 h later. Whereas increasing enzyme activities of the glycolate pathway apparently reduces glycolate excretion in Mougeotia , activation of CO₂ pumps seems to be the dominant reaction to prevent glycolate excretion in Eremosphaera . Mesostigma viride is one of the phylogenetically oldest algae in the group of Charophyceae . As this alga has already been demonstrated to contain microbodies with enzymes of leaf peroxisomes, the peroxisomal glycolate pathway must have originated at a very early stage. Surprisingly, the organelles from Mesostigma contain also the glyoxysomal marker enzyme isocitrate lyase suggesting these microbodies to be prototypes from which both glyoxysomes and leaf peroxisomes evolved.     

A multi-locus time-calibrated phylogeny of the siphonous green algae

The siphonous green algae are an assemblage of seaweeds that consist of a single giant cell. They comprise two sister orders, the Bryopsidales and Dasycladales. We infer the phylogenetic relationships among the siphonous green algae based on a five-locus data matrix and analyze temporal aspects of their diversification using relaxed molecular clock methods calibrated with the fossil record. The multi-locus approach resolves much of the previous phylogenetic uncertainty, but the radiation of families belonging to the core Halimedineae remains unresolved. In the Bryopsidales, three main clades were inferred, two of which correspond to previously described suborders (Bryopsidineae and Halimedineae) and a third lineage that contains only the limestone-boring genus Ostreobium. Relaxed molecular clock models indicate a Neoproterozoic origin of the siphonous green algae and a Paleozoic diversification of the orders into their families. The inferred node ages are used to resolve conflicting hypotheses about species ages in the tropical marine alga Halimeda.     

Differential sensitivity of green algae to allelopathic substances from Chara

Three short-term laboratory experiments were conducted to investigate allelopathic effects of a mixture of Chara globularis var. globularis Thuillier and Chara contraria var. contraria A. Braun ex Kützing on three different green algae. Single phytoplankton species were exposed to filtered water originating from charophyte cultures. Phytoplankton growth was monitored by determination of chlorophyll concentrations in batch cultures. The change in chlorophyll concentration during the experiments was analysed with a logistic growth model, resulting in an estimate of the exponential growth rate and the duration of the lag phase of the single green algae. The results indicate allelopathic effects of Chara on the growth of the green algae Selenastrum capricornutum Printz and Chlorella minutissima Fott et Nováková, whereas Scenedesmus obliquus (Turpin) Kützing did not seem to be affected. The exponential growth rate of S. capricornutum decreased 7% in the presence of water from a charophyte culture, while the growth rate of C. minutissima decreased with 3%. The allelopathic effect of Chara did not increase when the green alga C. minutissima was P-limited. The effect of Chara was different when young sprouts were used. With young sprouts the duration of the lag phase of C. minutissima was extended (25%), whilst for old plants the growth rate of this green alga decreased. Although the inhibiting effect of charophytes on specific phytoplankton species is rather small, the differential sensitivity of the species to Chara might influence the composition and biomass of phytoplankton communities in the field.     

Co-isolation of high-quality DNA and RNA from coenocytic green algae

A protocol is presented for the simultaneous isolation of DNA and RNA from giant-celled green algae. The overall quality of the DNA was examined by the A²⁶⁰/A²⁸⁰ ratio, agarose gel electrophoresis, and restriction enzyme analysis. Denaturing gel electrophoresis and cDNA cloning were used to investigate the quality of the RNA. These assays indicated that both the DNA and RNA isolated by this procedure are of high quality, suitable for further molecular analyses. Since many of these algae are slow growing and therefore only a few grams may be available, the isolation of DNA and RNA from the same plant material has obvious advantages.Abbreviations: Etbr, ethidium bromide.