Enhanced eicosapentaenoic acid production by Navicula saprophila

Changes in the eicosapentaenoic acid (EPA) content of Navicula saprophila grown photoautotrophically and mixotrophically with the addition of acetate were examined in terms of their growth progress. Among four conditions, mixotrophic conditions in CO₂-enriched (about 2%) atmosphere gave a maximum EPA content. As sodium acetate was added to the growth medium, the EPA content increased and reached a maximum value of 34.6 mg EPA g^-1 biomass in the early stationary growth phase. In contrast, under photoautotrophic conditions in CO₂ enriched atmosphere, the EPA content decreased during this phase. EPA was localized as the fatty acid esters of monogalactosyl diacylglycerol, phosphatidylethanolamine and phosphatidylcholine, and the addition of acetate strongly enhanced production of the PC ester of EPA. This revised version was published online in June 2006 with corrections to the Cover Date.     

Occurrence of phosphatidylsulfocholine, the sulfonium analog of phosphatidylcholine in some diatoms and algae

A survey of seven species of diatoms, one Euglena sp. and one dinoflagellate sp. for the presence of phosphatidylsulfocholine (PSC), the sulfonium analog of phosphatidylcholine (PC), was carried out using 1H-NMR spectroscopy and ammonia desorption chemical ionization mass spectrometry. PSC alone was found only in a non-photosynthetic diatom, Nitzschia alba. PSC, together with PC, was found in four of the diatoms (Nitzschia angularis, Cylindrotheca fusiformis, Phaeodactylum tricornutum and Navicula pelliculosa) in proportions of 6-24% of the total PC + PSC fraction, but little or no PSC (less than 2%) was detected in the remaining two (Cyclotella nana and Navicula incerta). Little or no PSC (less than 2%) was detected in a Euglena sp. by 1H-NMR but its presence was confirmed by 35S-labeling. The amount of PSC, if any, in the dinoflagellate (Amphidinium carterae) was below the level of detection by 1H-NMR.     

PHYSIOLOGICAL CHARACTERIZATION OF SIX LIPID-PRODUCING DIATOMS FROM THE SOUTHEASTERN UNITED STATES1

Six strains of diatoms from intertidal waters were isolated as part of the SERI Aquatic Species Program collection and screening effort: Amphiprora hyalina Greville, Cyclotella cryptica Reimann, Lewin & Guillard, Navicula acceptata Hustedt (two strains, NAVIC6 and NAVIC8), Navicula saprophila Lange-Bertalot & Bonik, and Nitzschia dissipata (Kütz.) Grunow. Among numerous algal strains isolated as part of this collection effort, these six strains showed rapid growth and elevated lipid content in preliminary screening experiments and were chosen for further physiological characterization. N. dissipata grew most rapidly at 25°C, whereas the other five strains grew best at 30–35°C. Salinity tolerance varied among strains, with maximal growth occurring at the following conductivities: 10–60 mS.cm^?1 (A. hyalina and N. acceptata NAVIC8), 10–35 mS.cm^?1 (C. cryptica), 20–45 mS.cm^?1 (N. acceptata NAVIC6), 10 mS.cm^?1 (N. saprophila), and 20–35 mS.cm^?1 (N. dissipata). The diatoms also differed in their utilization of nitrogen sources with A. hyalina growing optimally with either nitrate or urea; N. acceptata NAVIC6, with either nitrate or ammonium; C. cryptica, N. acceptata NAVIC8, and N. dissipata, with nitrate; and N. saprophila, with urea. Under optimal conditions, A. hyalina grew at 2.0 doublings. day^?1; C. cryptica grew at 3.0 doublings. day^?1. Each Navicula strain had a growth rate of 3.8 doublings. day^?1, and N. dissipata grew at 2.6 doublings.day^?1. All six strains had lipid contents in excess of 37% ashfree dry weight (AFDW) under nutrient-limited conditions, with N. saprophila having the highest lipid content at 48% AFDW.     

Screening of diatoms for heterotrophic eicosapentaenoic acid production

Nine strains of diatoms (representing four species) were screened for their ability to produce eicosapentaenoic acid (EPA) when cultured heterotrophically on glucose. Four strains were able to produce EPA heterotrophically using glucose as its carbon and energy source. Of the four,Nitzschia laevis was the best EPA producer, yielding 0.017 g g^–1 dry cell weight.N. laevis was the only species tested which synthesised more EPA heterotrophically than photosynthetically. This study shows thatN. laevis is a potential source of EPA production using heterotrophic culture conditions with glucose as the carbon and energy substrate.Author for correspondence     

DNA NUCLEOSIDE COMPOSITION AND METHYLATION IN SEVERAL SPECIES OF MICROALGAE1

Total DNA was isolated from 10 species of microalgae, including representatives of the Chlorophyceae (Chlorella ellipsoidea, Chlamydomonas reinhardtii, and Monoraphidium minutum), Bacillariophyceae (Cyclotella cryptica, Navicula saprophila, Nitzschia pusilla, and Phaeodactylum tricornutum), Charophyceae (Stichococcus sp.), Dinophyceae (Crypthecodinium cohnii), and Prasinophyceae (Tetraselmis suecica). Control samples of Escherichia coli and calf thymus DNA were also analyzed. The nucleoside base composition of each DNA sample was determined by reversed-phase high performance liquid chromatography. All samples contained 5-methyldeoxycytidine, although at widely varying levels. In M. minutum, about one-third of the cytidine residues were methylated. Restriction analysis supported this high degree of methylation in M. minutum and suggested that methylation is biased toward 5′-CG dinucleotides. The guanosine + cytosine (GC) contents of the green algae were, with the exception of Stichococcus sp., consistently higher than those of the diatoms. Monoraphidium minutum exhibited an extremely high GC content of 71%. Such a value is rare among eukaryotic organisms and might indicate an unusual codon usage. This work is important for developing strategies for transformation and gene cloning in these algae.     

Species composition of phytobenthos in the littoral of Lake Xolotlán (Managua)

The species composition of the phytobenthos in the littoral of Lake Xolotlán (Managua) was determined. Sampling was carried out in November 1987 (end of the rainy season) and in July–August 1988 (rainy season). Sixty-eight taxa were identified;viz. 47 Bacillariophyceae, 13 Cyanophyta and 8 Chlorophyta. The presence of diatom species likeNavicula veneta, Nitzschia amphibia andNitzschia palea indicate eutrophic conditions, high ionic concentration, alkaline conditions and intense organic pollution.     

Effects of 2E,4E-Decadienal on Motility and Aggregation of Diatoms and on Biofilm Formation

Phototrophic biofilm formation and dynamics result from the interaction between several parameters, including chemical interactions. Some of the secondary metabolites released by microalgae can influence the composition of benthic communities. We determined the effects of decadienal (DD), a polyunsaturated aldehyde produced by diatoms, on a benthic diatom, Fistulifera saprophila. At 5?μg?ml(-1), DD reduced cell motility by 88% and cell adhesion to the substrate by 91%. The effects occurred in less than 30?min. Using a fluorescent probe, we showed that DD could induce nitric oxide (NO) accumulation in F. saprophila cells. Cells exposed to a NO donor presented reduced adhesion and motility, which suggests the involvement of this cellular messenger in the mode of action of DD. Short-term experiments in microcosms showed that the presence of DD on a substrate strongly inhibited biofilm formation. Moreover, when the biofilm was bispecific, DD modified the proportion of the two species present. This indicates that the presence of DD-producing diatoms in a biofilm may favor the presence of certain microalgae at the expense of others. In addition to the effects on adhesion and motility, DD induced the formation of aggregates of F. saprophila cells. Aggregation was independent of NO production. Complementary experiments were performed with two other benthic diatoms, Nitzschia palea and Mayamea atomus. They showed that the effects of DD on adhesion and aggregation were species-dependent.     

MORPHOLOGY OF THE MARINE DIATOM NITZSCHIA NAVIS-VARINGICA, SP. NOV. (BACILLARIOPHYCEAE), ANOTHER PRODUCER OF THE NEUROTOXIN DOMOIC ACID

A new marine diatom, Nitzschia navis-varingica , sp. nov., isolated from Vietnamese waters, is described by light, transmission, and scanning electron microscopy, including thin sectioning. The new species has been found to produce the neurotoxin domoic acid (DA), better known from several species of Pseudo-nitzschia Peragallo and one species of Amphora Ehrenberg. Production of DA is therefore more widespread among diatoms than previously thought. Taxonomically, the genus Nitzschia Hassall is exceptionally difficult, with about 900 described taxa. Grunow (in Cleve and Grunow 1880 divided the genus into 24 sections, and this system is still used with modifications. Nitzschia navis-varingica , sp. nov. fits best into a group of sections that includes Dubiae, Bilobatae , most of the Lanceolatae , and Lineares , all sensu Grunow, as the cell is slightly indented in the middle in girdle view and has a moderately eccentric raphe and a weak longitudinal fold on the valve. Many species within these sections have features similar to N. navis-varingica , but no species seems to be identical. Because both Pseudo-nitzschia and Nitzschia belong to the family Bacillariaceae, it seems reasonable to look for further producers of DA in this family, including freshwater species, which mainly comprise species within the sections Dubiae, Bilobatae, Lanceolatae , and Lineares.     

The effects of dissolved heavy metals on attached diatoms in the Uintah Basin of Utah,U.S.A.

The relationships of diatom species to dissolved heavy metals in the streams of the Uintah Basin of Utah were studied through four seasons of 1977–1978. Niche center gradient analysis, cluster analysis and correlation analysis were performed.Achnanthes minutissima, Cyclotella meneghiniana, Cymbella minuta, Gomphonema parvulum, Navicula secreta var.apiculata, Nitzschia frustulum, Nitzschia frustulum var.perminuta, Nitzschia frustulum var.perpusilla, Nitzschia palea, andSynedra ulna appear to be indicator species of high or low heavy metal concentrations. Several other species also showed meaningful relationships to high or low heavy metal concentrations.Dept. of Physics and Astronomy, Brigham Young UniversityDept. of Physics and Astronomy, Brigham Young University     

Diatom communities in small water bodies at H. Arctowski Polish Antarctic Station (King George Island, South Shetland Islands, Antarctica)

An investigation of ponds, puddles and slow-flowing waters situated in the area of the Polish Antarctic Station distinguished two groups of diatom communities. The first group characterized waters poor in nutrients and brackish. The number of taxa, abundance of species and diatom biomass index were all low. Nitzschia homburgiensis, Achnanthes laevis var. quadratarea and A. delicatula prevailed. The second group characterized water richer in nutrients and brackish. The number of species was also low, but the diatom biomass index was higher. Nitzschia gracilis, Navicula gregaria and Navicula wiesneri formed large populations. Received: 17 May 1996 / Accepted: 20 September 1997     

Composition and dynamics of a highly diverse diatom assemblage in a limestone stream

The algal assemblages of a small limestone stream were studied for a year at monthly intervals. Algal standing crop was permanently high (mean concentration of 158 mg Chl-a · m^–2), but it reached the maximum values in spring and summer. Diatoms were dominant in the algal assemblages throughout this time, and more than one hundred species were recorded during the survey. Most of them are characteristic of hard waters, but others, mainly occurring in summer, have been observed elsewhere in moderately halophile waters.A striking succession was observed in the diatom assemblage in the stream in each season. This succession, with a maximum in summer, was mainly related with the lessening in flow and the increase in water mineralization. Moreover, the diversity of the samples increased sharply from April 1982 to July 1983. In fact, a progressive increase in salinity tolerant species could be observed from winter and spring to summer. Nitzschia sociabilis, Navicula gregaria, Navicula lanceolata and Gomphonema olivaceum were the most abundant species in winter, whereas Achnanthes minutissima reached its maximum in spring and Navicula schroeterii, Nitzschia thermaloides and Cyclotella meneghiniana were some of the most abundant in summer.     

增江底栖硅藻种类多样性及分布特征

2010年1月和5月对东江水系重要支流增江进行底栖硅藻的采样调查,分析了增江流域底栖硅藻的多样性和时空分布特征,并探讨了硅藻优势种与环境因子的关系.结果表明,两次采样共检出底栖硅藻42属178种(包括亚种和变种),与1月份相比,由于5月份降雨量较大,硅藻的数量有所下降,种类组成也有所改变.在两次采样中,藻类分布从下游到...     

GENETIC TRANSFORMATION OF THE DIATOMS CYCLOTELLA CRYPTICA AND NAVICULA SAPROPHILA

Two species of diatoms were genetically transformed by introducing plasmid vectors containing the Escherichia coli neomycin phosphotransferase II (npt II ) gene. Expression of the bacterial npt II gene in the diatoms was achieved using the putative promoter and terminator sequences from the acetyl-CoA carboxylase gene from the centric diatom Cyclotella cryptica T13L Reimann, Lewin, and Guillard. The vectors were introduced into C. cryptica and the pennate diatom Navicula saprophila NAVIC1 Lange-Bertalot and Bonik by microprojectile bombardment. Putative transformants were selected based on their ability to grow in the presence of the antibiotic G418, and production of the neomycin phosphotransferase protein by the transformed cells was confirmed by western blotting. The foreign DNA integrated into one or more random sites within the genome of the transformed algal cells, often in the form of tandem repeats. This is the first report of reproducible, stable genetic transformation of a chlorophyll c -containing alga .     

The development of marine biofilms on two commercial non-biocidal coatings: a comparison between silicone and fluoropolymer technologies

The antimicrobial performance of two fouling-release coating systems, Intersleek 700? (IS700; silicone technology), Intersleek 900? (IS900; fluoropolymer technology) and a tie coat (TC, control surface) was investigated in a short term (10 days) field experiment conducted at a depth of ca 0.5 m in the Marina Bandar Rawdha (Muscat, Oman). Microfouling on coated glass slides was analyzed using epifluorescence microscopy and adenosine-5'-triphosphate (ATP) luminometry. All the coatings developed biofilms composed of heterotrophic bacteria, cyanobacteria, seven species of diatoms (2 species of Navicula, Cylindrotheca sp., Nitzschia sp., Amphora sp., Diploneis sp., and Bacillaria sp.) and algal spores (Ulva sp.). IS900 had significantly thinner biofilms with fewer diatom species, no algal spores and the least number of bacteria in comparison with IS700 and the TC. The ATP readings did not correspond to the numbers of bacteria and diatoms in the biofilms. The density of diatoms was negatively correlated with the density of the bacteria in biofilms on the IS900 coating, and, conversely, diatom density was positively correlated in biofilms on the TC. The higher antifouling efficacy of IS900 over IS700 may lead to lower roughness and thus lower fuel consumption for those vessels that utilise the IS900 fouling-release coating.     

Extracts of North Sea macroalgae reveal specific activity patterns against attachment and proliferation of benthic diatoms: a laboratory study

A variety of macroalgae (Ceramium rubrum, Corallina officinalis, Palmaria palmata, Mastocarpus stellatus, Fucus vesiculosus, Cladophora rupestris, Ulva sp.) were investigated by scanning electron microscopy to visualize epiphytic colonizers. The macroalgae differed in terms of their epiphytic coverage of bacteria, fungi and diatoms. Macroalgae, largely devoid of epiphytic diatoms, were hypothesized to employ effective antifouling means to reduce epiphytic coverage, whilst heavily fouled macroalgae were proposed to lack antifouling strategies. To test these hypotheses from an allelochemical perspective with regard to fouling diatoms, dichloromethane-methanol (1:1) crude extracts of macroalgae were concentrated in dimethylsulfoxide and investigated in diatom attachment and proliferation assays using four benthic diatoms (Nitzschia sp., Navicula phyllepta, Navicula arenaria and Amphora sp.). Algal extracts exhibited a distinct pattern of activity against the test diatoms, suggesting a targeted and selective effect of macroalgal metabolites on individual fouling diatoms. The main outcome of this study was that visual inspection and quantitative categorization of epiphytic colonizers on macroalgal thalli could not be used to predict reliably whether macroalgae employed a chemical defense mechanism.     

The amino acid and gross composition of marine diatoms potentially useful for mariculture

The amino acid and gross compositions of three benthic diatoms (Cylindrotheca fusiformis Reimann and Lewin, Navicula jeffreyi Hallegraeff et Burford and Nitzschia closterium (Ehr. W. Smith) and three chain-forming diatoms (Lauderia annulata Cleve, Skeletonema costatum (Greville) Cleve and a tropical Skeletonema sp. (CS-252)), were determined during late-logarithmic growth phase.Four of the six species were rich in protein, ranging from 31% (S. costatum) to 38% (N. closterium) of the dry weight, and contained 4.9 to 6.5% carbohydrate and 9.4 to 18% ash. The other two species, C. fusiformis and L. annulata contained only 16% protein but had nearly twice the total carbohydrate (11 to 12%) and two to three times the ash (29 to 35%) of the other species. All species contained a similar percentage of lipid (18 to 20%), and a high protein quality based on their total amino acid composition.The usefulness of these diatoms for mariculture will be determined by growth rates, gross composition and acceptability to the animal. N. closterium had the fastest growth rates of the benthic mat-forming diatoms, it was rich in protein, and it may be a good candidate for abalone culture. The two Skeletonema spp. had the fastest growth rates of the chain-forming diatoms, and are already widely used for prawn larval culture in Australia. Feeding trials are now necessary to confirm the high nutritional value of these diatom species for specific animals.     

汾河水库及河道中优势硅藻生态位的研究

采用Levins生态位宽度公式和Petrailis生态位特定重叠指数测定了汾河水库和河道中 5 0个主要硅藻种的生态位宽度和生态位重叠 ,并对生态位宽度和生态位重叠的关系进行了初步探讨 ,结果表明 ,着生硅藻中的原子舟形藻、眼斑小环藻、平卧桥弯藻、尖菱形藻、短小舟形藻、线形曲壳藻、阿尔夫舟形藻等生态位最大 ,浮游硅藻中 ,以具星小环藻、团聚小环藻、眼斑小环藻生态位最宽 ;同时表明 ,生态位宽度大的种与其它种的生态位重叠也较大。生态位重叠表明 ,着生硅藻中 ,生态位重叠普遍偏高 ,河道中 ,清洁水体指示种普通等片藻进攻性最强 ,水库中以α -中污和 β-中污带生物比索曲壳藻进攻性最高。从生态位普遍重叠指数分析 ,浮游硅藻明显小于着生硅藻 ,表明浮游生境下 ,硅藻分化明显 ,着生环境中 ,硅藻对资源利用充分     

产二十二碳六烯酸等多不饱和脂肪酸真菌的筛选*

从土壤中筛选出一株产二十二碳六烯酸（DHA）的丝状真菌,菌丝含油21.23％,DHA占总脂肪酸2.51％;同时含二十碳五烯酸（EPA）,占总脂肪酸的0．41％;不饱和脂肪酸占总脂肪酸的80％。经鉴定为头孢霉属（Caphalosporiumsp．）真菌。同时发现两株菌含EPA,经鉴定为小克银汉霉（Cunninghamellasp.）和毛霉（Mucorsp．）。在这几个属中发现DHA和EPA尚属首次。头孢霉菌DHA产量及百分含量和斜面菌种在不同温度下储藏有关。菌种在20℃储藏10天,在液体PDA培养基上发酵,DHA可占总脂肪酸11．27％,产量达63．35mg／L。     

SALT‐INDUCED ALTERATIONS IN LIPID COMPOSITION OF DIATOM NITZSCHIA LAEVIS (BACILLARIOPHYCEAE) UNDER HETEROTROPHIC CULTURE CONDITION1

The diatom Nitzschia laevis Hust. is a potential producer of eicosapentaenoic acid (EPA). To elucidate its cellular response to salt stress, the effects of salinity on EPA production, lipid composition, and fatty acid distribution in the lipid pool were investigated. The highest contents of total fatty acids, EPA, and polar lipids were all obtained at NaCl of 20 g · L^?1, under which 71.3% of total EPA existed in polar lipid fractions. In N. laevis, high salt concentration might induce the decrease in neutral lipids (NLs), whereas the production of polar lipids, including phospholipids (PLs) and glycolipids (GLs), was enhanced. The degree of fatty acid unsaturation of both neutral and polar lipid fractions increased sharply when NaCl concentration increased from 10 to 20 g · L^?1 but decreased at NaCl concentration of 30 g · L^?1. The amount of total free sterols was increased with the increase in salt concentration. All these changes in lipid and fatty acids suggested a decrease in membrane permeability and fluidity under high salt concentration, which could help the alga acclimate to the salinity stress.     

Antifouling activities of octocorals on some marine microfoulers

The antifouling activities of vacuum-dried 70% aqueous alcohol extracts of four gorgonian and five soft corals against four dominant marine fouling diatoms (Navicula subinflata Grun, N. crucicula Smith, Amphora sp., Nitzschia sp.) are described. Of the 36 possible combinations (9 corals x 4 diatoms) 23 of the interactions (64%) showed 100% activity. Extracts of the gorgonian coral Echinogorgia complexa Nutting and the soft coral Dendronephthya (Morchellana) sp. showed 100% growth inhibition against all four fouling diatoms, implying the presence of potent broad spectrum antifouling compounds; other extracts showed more limited species specificity. Exposed cells when transferred to extract-free media, resumed normal growth indicating a nontoxic way of action. The effective concentration for 50% growth inhibition of the attached cells (EC50) varied for each extract and test organism used. The EC50 values for the extract of the gorgonian coral E. complexa against the fouling diatoms ranged from 86 microg/ml (N. subinflata) to 505 microg/ml (Amphora sp.) whereas the EC50 values for extracts of the soft coral Dendronephthya (Morchellana) sp. varied from 28 microg/ml (N. crucicula) to 415 microg/ml (Amphora sp.). The results support the hypothesis that octocorals contain antifouling agents, which could be exploited for the development of nontoxic natural antifouling technology.