Evidence for high iron requirements of colonial Phaeocystis antarctica at low irradiance

We have carried out field and laboratory experiments to examine the iron requirements of colonial Phaeocystis antarctica in the Ross Sea. In December 2003, we performed an iron/light-manipulation bioassay experiment in the Ross Sea polynya, using an algal assemblage dominated by colonial Phaeocystis antarctica, collected from surface waters with an ambient dissolved Fe concentration of ∼0.4 nM. Results from this experiment suggest that P. antarctica growth rates were enhanced at high irradiance (∼50% of incident surface irradiance) but were unaffected by iron addition, and that elevated irradiance mediated a significant decrease in cellular chlorophyll a content. We also conducted a laboratory iron dose–response bioassay experiment using a unialgal, non-axenic strain of colonial P. antarctica and low-iron (<0.2 nM) filtered seawater, both collected from the Ross Sea polynya in December 2003. By using rigorous trace-metal clean techniques, we performed this dose–response iron-addition experiment at ∼0°C without using organic chelating reagents to control dissolved iron levels. At the relatively low irradiance of this experiment (∼20 μE m⁻² s⁻¹), estimated nitrate-specific growth rate as a function of dissolved iron concentration can be described by a Monod relationship, yielding a half-saturation constant with respect to growth of 0.45 nM dissolved iron. This value is relatively high compared to reported estimates for other Antarctic phytoplankton. Our results suggest that seasonal changes in the availability of both iron and light play critical roles in limiting the growth and biomass of colonial Phaeocystis antarctica in the Ross Sea polynya.     

The pigment composition of Phaeocystis antarctica (Haptophyceae) under various conditions of light,temperature, salinity,and iron

The pigment composition of Phaeocystis antarctica was monitored under various conditions of light, temperature, salinity, and iron. 19′‐Hexanoyloxyfucoxanthin (Hex‐fuco) always constituted the major light‐harvesting pigment, with remarkably stable ratios of Hex‐fuco‐to‐chl a under the various environmental conditions. Increased pigment‐to‐chl a ratios at low irradiance confirmed the light‐harvesting function of Fucoxanthin (Fuco), 19′‐Hexanoyloxy‐4‐ketofucoxanthin (Hex‐kfuco), 19′‐butanoyloxyfucoxanthin (But‐fuco), and chl c2 and c3. Increased pigment‐to‐chl a ratios at high irradiance, low iron concentrations, and to a lesser extent at high salinity confirmed the photoprotective function of diadinoxanthin, diatoxanthin, and ß,ß‐carotene. Pigment ratios were not always according to expectations. The consistent increase in But‐fuco/chl at high temperature, high salinity, and low iron suggests a role in photoprotection rather than in light harvesting. Low Hex‐kfuco/chl ratios at high salinity were consistent with a role as light harvester, but the high ratios at high temperature were not, leaving the function of Hex‐kfuco enigmatic. Dedicated experiments were performed to test whether or not the light‐harvesting pigment Fuco could be converted into its structural relative Hex‐fuco, and vice versa, in response to exposure to light shifts. Rapid conversions could not be confirmed, but long‐term conversions cannot be excluded. New pigment ratios are proposed for chemotaxonomic applications. The ratios will improve pigment‐based diagnosis of algal species in waters dominated by P. antarctica.     

An examination of the role of colonial <Emphasis Type="Italic">Phaeocystis antarctica</Emphasis> in the microbial food web of the Ross Sea

The extensive buildup of phytoplankton biomass in the Ross Sea conflicts with the view that high rates of herbivory occur in all regions of the Southern Ocean. Nano and microplanktonic consumers comprise a significant fraction of total plankton biomass; however, the importance of grazing remains uncertain in the Ross Sea. Microzooplankton ingestion of solitary and colonial cells of Phaeocystis antarctica were calculated using a novel live-staining fluorescently-labeled algae method. Different morphotypes of P. antarctica were stained different colors, mixed, and observed inside Euplotes to determine their feeding preference. The blue (7-aminocoumarin) (CMAC) stain was used on the colonies and the green (CMFDA) CellTracker Probe was used on solitary cells. Both morphotypes can be seen inside the food vacuoles of the ciliate, supporting the idea that microzooplankton are capable of ingesting cells within the colonial matrix. This suggests that P. antarctica colonies enter the microbial loop in the Ross Sea before sedimentation.     

COLONY SIZE OF PHAEOCYSTIS ANTARCTICA (PRYMNESIOPHYCEAE) AS INFLUENCED BY ZOOPLANKTON GRAZERS1

The haptophyte Phaeocystis antarctica G. Karst. is a dominant phytoplankton species in the Ross Sea, Antarctica, and exists as solitary cells and mucilaginous colonies that differ by several orders of magnitude in size. Recent studies with Phaeocystis globosa suggest that colony formation and enlargement are defense mechanisms against small grazers. To test if a similar grazer‐induced morphological response exists in P. antarctica, we conducted incubation experiments during the austral summer using natural P. antarctica and zooplankton assemblages. Dialysis bags that allowed exchange of dissolved chemicals were used to separate P. antarctica and zooplankton during incubations. Geometric mean colony size decreased by 35% in the control, but increased by 30% in the presence of grazers (even without physical contact) over the 15 d incubation. The estimated colonial‐to‐solitary cell carbon ratio was significantly higher in the grazing treatment. These results suggest that P. antarctica colonies would grow larger in the presence of indigenous zooplankton and skew the carbon partitioning significantly toward the colonial phase. While these observations show that the colony size of P. antarctica was affected by a chemical signal related to grazers, the detailed nature and ecological significance of this signal remain unknown.     

Diffusion of Fe(II) from an iron propagation cage and its effect on tissue iron and pigments of macroalgae on the cage

Iron propagation cages were settled on sand and/or rock beds in coastal areas of Hokkaido. The cage was oxidized by dissolved oxygen and the released Fe(II) diffused into the seawater around the cage. Fe(II) concentrations in the range of 10–50 nM were detected within a 20-m distance around the cage. For comparison, in the Japan Sea, the total iron concentration is less than 2 nM.Laminaria japonica was grown in an indoor semi-continuous culture system. The critical Fe level for maintaining maximum growth, and the subsistence Fe level for survival were measured. The concentrations obtained were 14–21 and 8 g Fe g^–1 tissue, respectively. Iron found inL. japonica growing on rocks and/or rock beds in the Japan Sea was close to the subsistence level. However, the Fe level inL. japonica on the cage in the Japan Sea was considerably higher. The concentrations of chlorophyll-a and fucoxanthin collected from the cage were significantly higher for sporophytes, demonstrating that iron is a very important element for the growth of seaweeds.     

COMPARATIVE EFFECTS OF LIGHT ON PIGMENTS OF TWO STRAINS OF EMILIANIA HUXLEYI (HAPTOPHYTA)1

Calcifying and a noncalcifying strains of Emiliania huxleyi were cultured in nutrient replete turbidostats under a photon flux density (PFD) gradient from 50 to 600 μmol E·m^?2·s^?1. For both strains, growth was PFD‐saturated at 300 μmol E·m^?2·s^?1. The strains, although with clearly different physiological properties due to the presence or absence of calcification, showed the same trends and magnitude of change in their pigment compliment as a function of PFD. Light‐controlled pigment composition and the trends of change in pigment composition were identical in both strains. Fucoxanthin (Fuco) was the major carotenoid in the calcifying strain, while in the noncalcifying strain this role was assumed by 19′ hexanoyloxyfucoxanthin (19 Hex). The photoprotective pigments and 19 Hex, normalized to chl a, increased with increasing light, while chl a content per cell and chl c's and Fuco, normalized to chl a, decreased with increasing PFD. The sum of all carotenoids normalized to chl a was remarkably similar in all PFDs used. Collectively, our results suggest that 19 Hex was synthesized from Fuco with light as a modulating factor and that the total amount of carotenoids is strain‐specific and synthesized/catabolized in tandem with chl a to a genetically predefined level independent of PFD.     

A preparative method for isolation of fucoxanthin from Eisenia bicyclis by centrifugal partition chromatography

Introduction – Eisenia bicyclis (Kjellman) Setchell (Laminariaceae) is a common brown alga that inhabits around the coast of Korea, Japan and China. It contains fucoxanthin, a major carotenoid of brown algae which shows a variety of pharmaceutical functions. Objective – The aim of this investigation was the quantification and preparative isolation of fucoxanthin from fresh E. bicyclis using a new separation scheme, centrifugal partition chromatography (CPC). Methodology – The fucoxanthin fraction (Fuco fraction) was prepared by solvent partition method from the acetone extract of fresh E. bicyclis. Fuco fraction was used for CPC using a two‐phase solvent system of n‐hexane–ethyl acetate–ethanol–water (5:5:7:3, v/v/v/v). The flow rate of mobile phase was 2 mL/min with descending mode while rotating at 1000 rpm. The eluate was monitored at 410 nm. The content and structure of fucoxanthin in the CPC fraction were confirmed with HPLC, UV, APCI/MS and NMR spectra. Results – A preparative CPC yielded 20 mg of fucoxanthin (87% recovery from Fuco fraction) in a two‐step separation from 516 mg of Fuco fraction containing 4.59% fucoxanthin. The purity of the isolated fucoxanthin was about 81% in the first CPC step and over 98% in the second CPC step based on the calibration curve. The isolated fucoxanthin was identified as all‐trans‐fucoxanthin with APCI/MS (parent ion at m/z 641 [M + H ? H₂O]⁺) and ¹H, ¹³C and 2‐D NMR spectra. Conclusion – High‐purity fucoxanthin was successfully isolated from fresh E. bicyclis, suggesting further potential applications in the industrial use of this valuable carotenoid. Copyright © 2011 John Wiley & Sons, Ltd.     

Biomass yields of Chlorella from iron (Y x/Fe) in iron-limited batch cultures

The maximum biomass in iron-limited photosynthetic batch cultures of chlorella increased as the logarithm of the iron concentration. The growth yield from iron (Y _x/Fe) showed a marked inverse relation to the specific growth rate. The maximum biomass yield, g dry biomass/g iron consumed, was 7.5x10³ with specific growth rate 0.108 h^-1; the minimum was 0.79×10³ with specific growth rate 0.145 h^-1. The maximum specific growth rate in the exponential phase of Fe limited cultures varied as the initial Fe concentration. Fe-limited growth made the cells adhere to a glass surface.Abbreviation O.D. optical density     

Iron limitation results in induction of ferricyanide reductase and ferric chelate reductase activities in Chlamydomonas reinhardtii

The green alga Chlamydomonas reinhardtii Dangeard CW-15 exhibited very low rates of plasma-membrane Fe(III) reductase activity when grown under Fe-sufficient conditions. After switching the medium to an Fe-free formulation, both ferricyanide reductase and ferric chelate reductase activities rapidly increased, reaching a maximum after 3 d under iron-free conditions. Both of the Fe(III) reductase activities increased in parallel over time, they exhibited similar K _m values (approximately 10 μM) with respect to Fe(III), displayed the same pH profile of activity, and both exhibited the same degree of light stimulation which could be inhibited by 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU). Furthermore, ferricyanide competitively inhibited ferric chelate reduction by iron-limited cells. These results indicate that both Fe(III) reductase activities were mediated by the same iron-limitation-induced plasma-membrane reductase. No evidence was found for the presence of Fe(III)-reducing substances in the culture medium, or for the involvement of active oxygen species in the process of Fe(III) reduction. Chlamydomonas reinhardtii appears to respond to iron limitation in a manner similar to Strategy I higher plants. Received: 24 June 1997 / Accepted: 2 August 1997     

Novel diaroylhydrazine ligands as iron chelators: coordination chemistry and biological activity

The search for orally effective drugs for the treatment of iron overload disorders is an important goal in improving the health of patients suffering diseases such as β-thalassemia major. Herein, we report the syntheses and characterization of some new members of a series of N-aroyl-N′-picolinoyl hydrazine chelators (the H₂IPH analogs). Both 1:1 and 1:2 Fe^III:L complexes were isolated and the crystal structures of Fe(HPPH)Cl₂, Fe(4BBPH)Cl₂, Fe(HAPH)(APH) and Fe(H3BBPH)(3BBPH) were determined (H₂PPH=N,N′-bis-picolinoyl hydrazine; H₂APH=N-4-aminobenzoyl-N′-picolinoyl hydrazine, H₂3BBPH=N-3-bromobenzoyl-N′-picolinoylhydrazine and H₂4BBPH=N-(4-bromobenzoyl)-N′-(picolinoyl)hydrazine). In each case, a tridentate N,N,O coordination mode of each chelator with Fe was observed. The Fe^III complexes of these ligands have been synthesized and their structural, spectroscopic and electrochemical characterization are reported. Five of these new chelators, namely H₂BPH (N-(benzoyl)-N′-(picolinoyl)hydrazine), H₂TPH (N-(2-thienyl)-N′-(picolinoyl)-hydrazine), H₂PPH, H₂3BBPH and H₂4BBPH, showed high efficacy at mobilizing ⁵⁹Fe from cells and inhibiting ⁵⁹Fe uptake from the serum Fe transport protein, transferrin (Tf). Indeed, their activity was much greater than that found for the chelator in current clinical use, desferrioxamine (DFO), and similar to that observed for the orally active chelator, pyridoxal isonicotinoyl hydrazone (H₂PIH). The ability of the chelators to inhibit ⁵⁹Fe uptake could not be accounted for by direct chelation of ⁵⁹Fe from ⁵⁹Fe–Tf. The most effective chelators also showed low antiproliferative activity which was similar to or less than that observed with DFO, which is important in terms of their potential use as agents to treat Fe-overload disease.     

Summer and spring trophic niche of larval and juvenile <Emphasis Type="Italic">Pleuragramma antarcticum</Emphasis> in the Western Ross Sea,Antarctica

The aim of this paper is to contribute to the knowledge on the feeding habits of larvae and juvenile Pleuragramma antarcticum in the western Ross Sea. In summer, the diet of P. antarcticum postlarvae (8–17 mm) was dominated by calanoid eggs (35.5%), Limacina (32.1%) and tintinnids (17.6%), while the principal food of juveniles consisted mainly of copepods (98.2%), with Oncaea curvata being the most abundant (85.1%) and the most frequently consumed prey. The food composition of P. antarcticum postlarvae (24–29 mm), collected in spring, suggest that they fed actively under the sea ice. Stephos longipes, Harpacticus furcifer and Paralabidocera antarctica sea ice copepods represent, in all their different developmental stages, the most abundant biomass food in Terra Nova Bay in this period. Our results therefore suggest that the diet of younger Pleuragramma specimens shifted in prey composition from the first summer to the following spring. This study draws attention to the key role of the copepod, P. antarctica, in the food web of Terra Nova Bay. This article belongs to a special topic: Five articles coordinated by L. Guglielmo and V. Saggiomo appear in this issue of Polar Biology and are a result of a workshop on Sea-ice communities in Terra Nova Bay (Ross Sea) held in August 2007 in Capo Calavà, Messina, Italy.     

Photosystem 2 photochemistry and pigment composition of a yellow mutant of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) under different irradiances

A yellow leaf colouration mutant (named ycm) generated from rice T-DNA insertion lines was identified with less grana lamellae and low thylakoid membrane protein contents. At weak irradiance [50 μmol(photon) m⁻² s⁻¹], chlorophyll (Chl) contents of ycm were ≈20 % of those of WT and Chl a/b ratios were 3-fold that of wild type (WT). The leaf of ycm showed lower values in the actual photosystem 2 (PS2) efficiency (Φ_PS2), photochemical quenching (q_P), and the efficiency of excitation capture by open PS2 centres 1 (F_v′/F_m′) than those of WT, except no difference in the maximal efficiency of PS2 photochemistry (F_v/F_m). With progress in irradiance [100 and 200 μmol(photon) m⁻² s⁻¹], there was a change in the photosynthetic pigment stoichiometry. In ycm, the increase of total Chl contents and the decrease in Chl a/b ratio were observed. Φ_PS2, q_P, and F_v′/F_m′ of ycm increased gradually along with the increase of irradiance but still much less than in WT. The increase of xanthophyll ratio [(Z+A)/(V+A+Z)] associated with non-photochemical quenching (q_N) was found in ycm which suggested that ycm dissipated excess energy through the turnover of xanthophylls. No significant differences in pigment composition were observed in WT under various irradiances, except Chl a/b ratio that gradually decreased. Hence the ycm mutant developed much more tardily than WT, which was caused by low photon energy utilization independent of irradiance.     

The Role of Iron and Dissolved Organic Carbon in the Absorption of Ultraviolet Radiation in Humic Lake Water

Absorption of solar ultraviolet radiation (UVR) in aquatic ecosystems is primarily controlled by dissolved organic carbon (DOC). The role of iron (Fe) has also been suggested to contribute to UVR attenuation either directly or by interactions with DOC. Here we present findings from three laboratory manipulations of Fe and DOC on changes to the dissolved UVR absorption (a_d,320) in a mid-latitude, dimictic, humic lake. In a laboratory simulation of lake turnover where anoxic, hypolimnetic water was oxygenated a_d,320 significantly increased from 23.3 to 81.7 m⁻¹ (p<0.0001). In a second laboratory experiment, addition of ferrous Fe to deoxygenated lake water increased a_d,320 upon reoxygenation up to a concentration of 1.0 mg l⁻¹ Fe, where a solubility saturation threshold may have been reached. In situ lake experiments were designed to simulate release of UV absorbing substances from anoxic sediments by placing 20-l carboys (open at the bottom, sealed at the top) onto the lake bottom. UV absorption at 320 nm increased over time for samples from within the experimental carboys. Finally, samples from several lake profiles and sediment experiments were analyzed for a_d,320, total Fe, and DOC. UV absorption of dissolved substances at 320 nm and total Fe concentration both increased with depth, however DOC remained relatively constant over depth. Furthermore, total Fe and spectral slope showed tight coupling up to 1 mg l⁻¹ total Fe in our survey analysis. Our results provide evidence for the importance of anoxic sediments as a source of ferrous iron and UV absorbing substances and suggest a role for ferric iron in increasing UVR and PAR absorption in lake water. We suggest that as this ferrous Fe oxidizes, its absorptive properties increase, and it may bind with dissolved organic matter, enabling it to remain in solution and thus increasing the dissolved absorption of lake water for extended periods of time.     

Novel iron complexes and chelators based on cis,cis-1,3,5-triaminocyclohexane: iron-mediated ligand oxidation and biochemical properties

 The interaction of Fe(II) and Fe(III) with the novel Fe(II) chelator N,N′N″-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane (referred to as tachpyr) gives rise to six-coordinate, low-spin, cationic complexes of Fe(II). Tachpyr also displays a cytotoxicity toward cultured bladder cancer cells that is believed to involve coordination of intracellular iron. The anaerobic reaction of tachpyr with Fe(II) salts affords the Fe(II)-tachpyr²⁺ complex, but in presence of oxygen, oxidative dehydrogenation of one or two of the aminomethylene group(s) of the ligand occurs, with formal loss of H₂: R—N(H)—C(H)₂—(2-py) → R—N=C(H)—(2-py)+H₂. The resulting mono- and diimino Fe(II) complexes (denoted as [Fe(tachpyr-H₂)]²⁺ and [Fe(tachpyr-2H₂)]²⁺) are an inseparable mixture, but they may be fully oxidized by H₂O₂ to the known tris(imino) complex Fe(II)[cis,cis-1,3,5-tris(pyridine-2-carboxaldimino)cyclohexane]²⁺ (or [Fe(tachpyr-3H₂)]²⁺). Cyclic voltammetry of the imino complex mixture reveals an irreversible anodic wave at +0.78 V vs. NHE. Tachpyr acts as a reducing agent toward Fe(IIII) salts, affording the same two Fe(II) imino complexes as products. Tachpyr also reductively removes Fe(III) from an Fe(III)(ATP)₃ complex (which is a putative form of intracellular iron), producing the two Fe(II) imino complexes. Novel N-alkylated derivatives of tachpyr have been synthesized. N-Alkylation has two effects on tachpyr: lowering metal affinity through increased steric hindrance, and preventing Fe(III) reduction because oxidative dehydrogenation of nitrogen is blocked. The N-methyl tachpyr derivative binds Fe(II) only weakly as a high-spin complex, and no complexation or reduction of Fe(III) is observed. Corresponding to their inability to bind iron, the N-alkylated chelators are nontoxic to cultured bladder cancer cells. A tach-based chelator with three N-propyleneamino arms is also synthesized. Studies of the chemical and biochemical properties of this chelator further support a relationship between intracellular iron chelation, iron reduction, and cytotoxicity. Received: 23 March 1998 / Accepted: 1 June 1998     

Iron-uptake in the Euryarchaeon Halobacterium salinarum

Iron-uptake is well studied in a plethora of pro- and eukaryotic organisms with the exception of Archaea, which thrive mainly in extreme environments. In this study, the mechanism of iron transport in the extremely halophilic Euryarchaeon Halobacterium salinarum strain JW 5 was analyzed. Under low-iron growth conditions no siderophores were detectable in culture supernatants. However, various xenosiderophores support growth of H. salinarum. In [⁵⁵Fe]–[¹⁴C] double-label experiments, H. salinarum displays uptake of iron but not of the chelator citrate. Uptake of iron was inhibited by cyanide and at higher concentrations by Ga. Furthermore, a K_M for iron uptake in cells of 2.36 μM and a V_max of approximately 67 pmol Fe/min/mg protein was determined. [⁵⁵Fe]-uptake kinetics were measured in the absence and presence of Ga. Uptake of iron was inhibited merely at very high Ga concentrations. The results indicate an energy dependent iron uptake process in H. salinarum and suggest reduction of the metal at the membrane level.     

STRATEGIES AND RATES OF PHOTOACCLIMATION IN TWO MAJOR SOUTHERN OCEAN PHYTOPLANKTON TAXA: PHAEOCYSTIS ANTARCTICA (HAPTOPHYTA) AND FRAGILARIOPSIS CYLINDRUS (BACILLARIOPHYCEAE)1

We investigated rates and mechanisms of photoacclimation in cultures of Phaeocystis antarctica G. Karst. and Fragilariopsis cylindrus (Grunow) Willi Krieg, phytoplankton taxa that each dominate distinct areas of the Ross Sea, Antarctica. Both P. antarctica and F. cylindrus acclimated to increases in irradiance by reducing the effective size of the pigment antenna (σPSII) via xanthophyll‐cycle activity and reductions in chl. While enhanced photoprotection facilitated increases in specific growth rate and eventually led to higher light‐saturated photosynthetic rates (P^cell_m) in P. antarctica, increases in those variables were much smaller in F. cylindrus. In response to a lower irradiance, relaxation of xanthophyll‐cycle activity led to an increase in σPSII in both taxa, which occurred much more slowly in F. cylindrus. A surprising increase in specific growth rate over the first 36 h of acclimation in P. antarctica may have facilitated the significant reductions in P^cell_m observed in that taxon. In general, P. antarctica acclimated more quickly to changes in irradiance than F. cylindrus, exhibited a wider range in photosynthetic rates, but was more susceptible to photoinhibition. This acclimation strategy is consistent with growth in deeply mixed water columns with variations in irradiance that allow time for repair. In contrast, the slower acclimation rates, extensive photoprotection, and low photoinhibition exhibited by F. cylindrus suggest that it does not require the same period for repair as P. antarctica and is best suited for growth in habitats with relatively uniform irradiance, such as shallow mixed layers or sea ice.     

Purification and characterization of UDP-glucose: anthocyanin 3′,5′-<Emphasis Type="Italic">O</Emphasis>-glucosyltransferase from <Emphasis Type="Italic">Clitoria ternatea</Emphasis>

A UDP-glucose: anthocyanin 3′,5′-O-glucosyltransferase (UA3′5′GT) (EC 2.4.1.-) was purified from the petals of Clitoria ternatea L. (Phaseoleae), which accumulate polyacylated anthocyanins named ternatins. In the biosynthesis of ternatins, delphinidin 3-O-(6″-O-malonyl)-β-glucoside (1) is first converted to delphinidin 3-O-(6″-O-malonyl)-β-glucoside-3′-O-β-glucoside (2). Then 2 is converted to ternatin C5 (3), which is delphinidin 3-O-(6″-O-malonyl)-β-glucoside-3′,5′-di-O-β-glucoside. UA3′5′GT is responsible for these two steps by transferring two glucosyl groups in a stepwise manner. Its substrate specificity revealed the regioselectivity to the anthocyanin′s 3′- or 5′-OH groups. Its kinetic properties showed comparable k _cat values for 1 and 2, suggesting the subequality of these anthocyanins as substrates. However, the apparent K _m value for 1 (3.89 × 10⁻⁵ M), which is lower than that for 2 (1.38 × 10⁻⁴ M), renders the k _cat/K _m value for 1 smaller, making 1 catalytically more efficient than 2. Although the apparent K _m value for UDP-glucose (6.18 × 10⁻³ M) with saturated 2 is larger than that for UDP-glucose (1.49 × 10⁻³ M) with saturated 1, the k _cat values are almost the same, suggesting the UDP-glucose binding inhibition by 2 as a product. UA3′5′GT turns the product 2 into a substrate possibly by reversing the B-ring of 2 along the C2-C1′ single bond axis so that the 5′-OH group of 2 can point toward the catalytic center. K. Kogawa, N. Kato, K. Kazuma, and N. Noda contributed equally to this work.     

Enumeration of bacteria from a Trichodesmium spp. bloom of the Eastern Arabian Sea: elucidation of their possible role in biogeochemistry

The carbon-flux via algal bloom events involves bacteria as an important mediator. The present study, carried out during the spring inter-monsoon month of April 2008 onboard CRV Sagar Manjusha-06 in the Eastern Arabian Sea, addresses the bloom-specific flow of carbon to bacteria via chromophoric dissolved organic matter (CDOM). Eleven stations monitored were located in the coastal, shelf and open-ocean areas off Ratnagiri (16°59′N, 73°17′E), Goa (15°30′N, 73°48′E) and Bhatkal (13°58′N, 74°33′E) coasts. Visible bloom of “saw-dust” color in the Ratnagiri shelf were microscopically examined and the presence of cyanobacteria Trichodesmium erythraeum and T. thieabautii with cell concentrations as high as 3.05 × 10⁶ trichomes L⁻¹ was recorded. Total bacterial counts (TBC) varied between 94.09 × 10⁸ cells L⁻¹ in the bloom to 1.34 × 10⁸ cells L⁻¹ in the non-bloom area. Chromophoric dissolved organic matter (CDOM) concentrations averaged 2.27 ± 3.02 m⁻¹ (absorption coefficient 325 nm) in the bloom to 0.28 ± 0.07 m⁻¹ in the non-bloom waters respectively. CDOM composition varied from a higher molecular size with lower aromaticity in the bloom to lower molecular size and increased aromaticity in the non-bloom areas respectively. Strong positive relationship of TBC with Chlorophyll a (R ² = 0.65, p < 0.01) and CDOM concentrations (R ² = 0.8373, p = 0.01) in the bloom area indicated hydrolysis and/or uptake of CDOM by bacteria. Absorption by mycosporine-like amino acid palythene (λ _max = 360 nm) was recorded in the filtrate of bloom. Morphotypes of Trichodesmium-associated bacteria revealed a higher frequency of Gram-positive rods. The role of bacteria in relation to changing CDOM nature and as a factor in affecting oxygen content of the water column is discussed in context of the Arabian Sea.     

Algal Carotenoids 51. Secondary carotenoids 2.Haematococcus pluvialis aplanospores as a source of (3S, 3′S)-astaxanthin esters

Aplanospores ofHaematococcus pluvialis MUR 145 contained 0.7% carotenoids (dry wt. basis) consisting of β,β-carotene (5% of total carotenoid), echinenone (4%), canthaxanthin (4%), (3S,3′S)-astaxanthin diester (34%), (3S,3′S)-astaxanthin monoester (46%), (3S,3′S)-astaxanthin (1%) and (3R,3′R,6′R)-lutein (6%). The astaxanthin esters were examined by TLC and HPLC and VIS,¹H NMR and mass spectra recorded. Their chirality was determined by the camphanate method (Vecchi & Müller, 1979) after anaerobic hydrolysis. The tough cell wall of the aplanospores required enzymatic treatment prior to pigment extraction. The potential use of this microalga as a feed ingredient in aquaculture is discussed briefly.