Showing papers in "Journal of Applied Phycology in 1996"

Isolation and purification of Australian isolates of the toxic cyanobacterium Microcystis aeruginosa Kutz

Abstract: Isolation and laboratory culture ofMicrocystis aeruginosa Kutz. using a growth medium (MLA medium) suitable for both non-axenic and axenic cultures is described. Seventeen established strains ofM. aeruginosa were subjected to one or more of three purification methods: centrifugation cleaning, sulphide gradient selection, and antibiotic treatment (Imipenem®). While each method purified only about half of the strains attempted, the selective application of each method, based on the morphological characteristics of the strains, succeeded in purifying 12 of the 17 strains. Three of the 5 strains not purified were contaminated with a sulphide-tolerant, Imipenem-resistant spirochaete,Spirochaeta cf.aurantia, which could not be detected on normal, broad spectrum bacterial test media. The presence of this bacterial species was detected only by phase contrast and DAPI (4,6-diamidino-2-phenylindole) stained fluorescence microscopy.

Enhanced leaf chlorophyll levels in plants treated with seaweed extract

Abstract: Application to the soil of an aqueous alkaline extract ofAscophyllum nodosum resulted in higher concentrations of chlorophyll in the leaves of treated plants in comparison to control plants treated with an equivalent volume of water. Positive results were obtained with all species tested (tomato, dwarf French bean, wheat, barley, maize). When the seaweed extract was applied as a foliar spray, similar effects on leaf chlorophyll contents were obtained, except in the case of dwarf French bean plants, for which no significant difference was recorded between test and control plants. When the betaines present in the seaweed extract were applied as a mixture in the same concentrations as those in the diluted seaweed extract (γ-aminobutyric acid betaine 0.96 mg L−1, δ-aminovaleric acid betaine 0.43 mg L−1, glycinebetaine 0.34 mg L−1), very similar leaf chlorophyll levels were recorded for the seaweed extract and betaine treated plants. This suggests strongly that the enhanced leaf chlorophyll content of plants treated with seaweed extract is dependent on the betaines present.

Productivity and photosynthetic efficiency of Spirulina platensis as affected by light intensity, algal density and rate of mixing in a flat plate photobioreactor

Abstract: The effect of the rate of mixing on productivity of algal mass in relation to photon flux density and algal concentration was quantitatively evaluated in cultures ofSpirulina platensis grown in a newly designed flat-plate photobioreactor. Special emphasis was placed on elucidating the principles underlying efficient utilization of high photon flux density for maximal productivity of algal-mass. Whereas the rate of mixing exerted little influence on productivity and photosynthetic efficiency in cultures of relatively low algal density, its effect became ever more significant as algal concentration was increased. Maximal mixing-enhanced cell concentrations and productivity of biomass were obtained at the highest light intensity used. At each level of incident light intensity, maximum productivity and photosynthetic efficiency could be achieved only when algal concentration and mixing rates were optimized. The higher the intensity of the light source, the higher became the optimal culture density, highest algal concentrations and productivity of biomass being obtained at the highest light intensity used. The rate of mixing required careful optimization: when too low, maximal productivity resulting from the most efficient utilization of light could not be obtained. Too high a rate of mixing resulted in cell damage and reduced output rate.

Recent advances in microalgal bioscience in Japan, with special reference to utilization of biomass and metabolites: a review

Abstract: Japan is one of leading countries in the utilization of and research on microalgae, and various findings have been obtained. Many papers, however, have been published in Japanese, which prevents the information spreading far and wide. The purpose of this review is to introduce recent advances in the utilization of microalgae as well as their basic research in Japan. The discussion covers practical applications ofChlorella andSpirulina biomass to health foods, food additives and feed supplements. The current use of microalgae as live feeds for larvae in aquaculture is also summarized. With respect to microalgal metabolites the present status of research is described with a greater emphasis on bioactive compounds, pigments and oils as potential drugs, coloring matters and biofuels, respectively.

Spirulina (Arthrospira) : potential application as an animal feed supplement

Abstract: Spirulina has been used as human food supplement for over 20 years, but its use as an animal feed supplement is relatively recent. This paper reviews earlier studies on its more established effects on growth, survival and tissue quality in a whole range of animals and more recent studies on its immunomodulatory, anti-viral and anti-cancer effects. The basis for potential application as an animal feed supplement is discussed.

Influence of high frequency light/dark fluctuations on photosynthetic characteristics of microalgae photoacclimated to different light intensities and implications for mass algal cultivation

Abstract: Oxygen evolution from aScenedesmus obliquus dominated outdoor culture was followed in a small volume chamber, irradiated either by continuous white light or under light/dark frequencies between 0.05 to 5000 Hz, using arrays of ‘high intensity’ red light emitting diodes (LED's). By placing neutral density filters in the path of the white light, light saturation curves of the oxygen evolution (P/I curves) were measured using diluted aliquots of algal cultures. The results clearly showed that photosynthetic rates increased exponentially with increasing light/dark frequencies, that a longer dark period in relation to the light period does not necessarily lead to higher photosynthetic rates (efficiencies), and that algae do not acclimate to a specific light/dark frequency. One of the most important factors that influenced photosynthetic rates, either under continuous illumination or intermittent, was whether the algae were dark or light acclimated. Low light/dark frequencies were perceived by the algae as low light conditions, whilst the opposite was true for high frequencies. The light utilisation efficiency in a fluctuating light/dark environment depended on the acclimated state of the algae, the specific frequency of the fluctuations and the duration of the exposure. Since the frequencies determined the ‘perceived’ quantities of light, dark reactions played an important role in determining the average photosynthetic efficiencies. These results have important implications for algal biotechnology.

Microscopic green algae and cyanobacteria in high-frequency intermittent light

Abstract: The effects of fluctuations in the irradiance onScenedesmus quadricauda, Chlorella vulgaris andSynechococcus elongatus were studied in dilute cultures using arrays of red light emitting diodes. The growth rate and the rate of photoinhibition were compared using intermittent and equivalent continuous light regimes in small-size (30 ml) bioreactors. The CO2 dependent photosynthetic oxygen evolution rates in the intermittent and continuous light regimes were compared for different light/dark ratios and different mean irradiances. The kinetics of the electron transfer reactions were investigated using a double-modulation fluorometer. The rates of photosynthetic oxygen evolution normalized to equal mean irradiance were lower or equal in the intermittent light compared to the maximum rate found in the equivalent optimal continuous light regime. In contrast, the growth rates in the intermittent light can be higher than the growth rate in the equivalent continuous light. Photoinhibition is presented as an example of a physiological process affecting the growth rate that occurs at different rates in the intermittent and equivalent continuous lights. The difference in the dynamics of the redox state of the plastoquinone pool is proposed to be responsible for the low photoinhibition rates observed in the intermittent light.

Prevention of fish oil rancidity by phlorotannins from Sargassum kjellmanianum

Abstract: Known only in the Phaeophyceae, phlorotannins (brown algal polyphenols) are a class of natural products with potential uses in pharmacology This study reports that phlorotannins from Sargassum kjellmanianum can prevent fish oil from rancidification; the antioxidation activity was about 26 times higher than that of 002% BHT (tertbutyl-4-hydroxytoluene)

Molecular genetics of the cyanobacterium Synechocystis sp. PCC 6803 : Principles and possible biotechnology applications

Abstract: The cyanobacteriumSynechocystis sp. PCC 6803 is readily amenable to targeted mutagenesis: Foreign DNA is taken up spontaneously, and after uptake DNA can be integrated into the organism's genome by homologous recombination. Using appropriate DNA constructs for transformation, specific genes in the organism can be interrupted, deleted, or replaced by modified gene copies. The organism can grow under a number of different conditions, ranging from photoautotrophic to fully heterotrophic modes, making genetic modifications that alter fundamental processes such as photosynthesis and/or respiration feasible. For example, deletion of photosystem I leads to an obligate (photo)heterotrophic strain in which photosystem II-generated electrons appear to be consumed by respiratory processes, whereas deletion of photosystem II leads to an obligate (photo)heterotrophic strain in which cyclic electron flow around photosystem I appears to remain active. A major advantage ofSynechocystis sp. PCC 6803 is that its entire genome has been sequenced (by S. Tabata and co-workers), opening many avenues to address basic and applied research problems. For example, genes can be introduced, modified or deleted, and hypotheses regarding the function of an open reading frame can be tested by deletion of this open reading frame. Methods to modify genes are numerous. In addition to site-directed mutagenesis, novel molecular genetic approaches including ‘targeted random mutagenesis’, combinatorial mutagenesis and introduction of hybrid genes have come of age and have proven to be very powerful tools in protein engineering. These approaches have been utilized primarily in this strain to study photosynthesis, but applications of this technology, including pathway engineering, alterations of substrate specificity of enzymes and introduction of tolerance to a variety of stresses, are equally feasible in relation to more applied aims. For optimal utilization of the potential of theSynechocystis sp. PCC 6803 system, however, an increased emphasis toward understanding the biochemistry and molecular physiology of cyanobacteria will also be critically important.

Comparison of cytokinin- and auxin-like activity in some commercially used seaweed extracts

Abstract: Six commercially used seaweed extracts were tested for cytokinin- and auxin-like activity using the soybean callus bioassay and the mung bean rooting bioassay respectively. All the seaweed extracts tested showed cytokinin-like activity. Seamac caused the most callus growth with activity being concentrated at R f 0.9 which co-chromatographed withiso-pentenyladenine and its riboside. The other five seaweed extracts yielded activity at R f 0.7–0.8. This co-chromatographed with zeatin and zeatin riboside. All the seaweed extracts tested improved rooting of mung beans. Kelpak made fromEcklonia maxima (Osbeck) Papenf. gave the best rooting response.

Screening of diatoms for heterotrophic eicosapentaenoic acid production

Abstract: 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.

Fish kills related to Prymnesium parvum N. Carter (Haptophyta) in the People's Republic of China

Abstract: Prymnesium parvum has been known to cause mass mortality of fish in PR of China since 1963. It usually occurs in brackish waters and inland high-mineral waters. The fish-breeding industry (mainly species of carp) in these regions of the PRC has been threatened by this microalga. Electron microscopic examination of isolates from Dalian and Tianjin revealed that the isolates wereP. parvum, based on specific scale patterns and two kinds of scales. The symptoms of the poisoned fish and the control of this toxic alga are also discussed. The addition of ammonium sulfate, copper sulfate, mud, reduced salinity and organic fertilizer to fish ponds has been partially successful in controlling blooms of this toxic alga. Adding 50–70 kg ha−1 day−1 manure (dry weight) to the fish pond to inhibitP. parvum from becoming the dominant species in the fish pond is recommended. A reduction in salinity to less than 2‰ is the easiest way to save freshwater fish from being poisoned byP. parvum. Use of ammonium sulfate is an efficient, economical and safer method to controlP. parvum than copper sulfate or mud.

Efficient utilization of high irradiance for production of photoautotropic cell mass: a survey

Abstract: For mass production of microalgae outdoors to be justified as a significant commercial entity, solar energy should be utilized at a much higher efficiency, yielding greatly increased photosynthetic productivity than presently obtained. Development of photobioreactors to provide an answer for this challenge rests at the root and the very future of this biotechnology. Most available Photobioreactors yield increased volumetric outputs of cell mass, but the areal yield which relates to the photosynthetic efficiency is rather similar to that obtained in the basically inefficient open raceway, the most prevalent commercial reactor today. The key for efficient utilization of the super saturating solar irradiance existing outdoors rests in distributing it, in effect, to as large a number of cells per given volume in as high a frequency as possible. This unfolds the design principles underlying efficient utilization of high irradiance for photoautotrophic production of cell mass: Reactors should be maximally exposed to sun light, have a narrow light-path coupled with a safe mixing system designed to create fast, turbulent streaming for moving the algal cells in and out of the photic volume at maximal frequency. Reactors designed along these principles may support ultrahigh cell densities resulting in high volumetric as well as areal yields, hopefully expanding thereby the economic basis of microalgal biotechnology.

Mixotrophic growth of Chlorella sorokiniana in outdoor enclosed photobioreactor

Abstract: Chlorella sorokiniana was cultured in heterotrophic or mixotrophic mode in outdoor enclosed tubular photobioreactor. The culture temperature was maintained at 32–35 °C. At night, theChlorella culture grew heterotrophically, and 0.1 M glucose was completely consumed. The biomass growth yield of glucose was 0.35 ± 0.001 g-biomass g-glucose−1. During the day, the algal culture grew mixotrophically and the biomass growth yield was 0.49 g-biomass g-glucose−1 in low density culture (initial biomass concentration, Xo = 2 g l−1), 0.56 g-biomass g-glucose−1 in medium density culture (Xo = 4 g l−1) and 0.46 g-biomass g-glucose−1 in high density culture (Xo = 7 g l−1). The daily area productivity of the culture, with Xo = 4 g l−1 corresponded to 127 g-biomass m−2 d−1 during the day and 79 g-biomass m−2 d−1 during the night. In all the cultures, the dissolved O2 concentration increased in the morning, reached the maximum value at noon, and then decreased in the afternoon. The dissolved CO2 concentration remained at 3 mBar in the morning and increased in the afternoon. Glycolate was not found to accumulate in culture medium.

Environmental effects on growth and biochemical composition of Nitzschia inconspicua Grunow

Abstract: The effects of nitrate and silicate levels, and carbon source on growth, biochemical composition and fatty acid composition ofNitzschia inconspicua were investigated using batch cultures. Within the range of silicate levels supplied (8.8–176 μM), no marked variations in growth trend, biochemical composition or fatty acid composition were shown. Biomass at stationary phase, ranging from 64–66 mg ash-free dry weight (AFDW) L−1, and specific growth rate (μ) based on chlorophylla (0.41–0.50 d−1) of the cultures grown within 0.3–3.0 mM NaNO3 were not significantly different. Cultures supplemented with glucose (0.1 % w/v), acetate (0.1 % w/v) or 5% CO2 attained higher biomass (85, 85, 97 mg AFDW L−1) than the control which was grown in synthetic seawater and agitated by magnetic stirring. Cells grown at <3.0 mM NaNO3 contained higher carbohydrate contents (14.8–21.5% AFDW) than those grown at 3.0 mM (4.0% AFDW). Lipid content increased at the expense of proteins in cells aerated with 5% CO2. The dominant fatty acids, 16:0 and 16:1, ranged from 35.7–45.0% and 36.4–45.4% total fatty acids (TFA), respectively, while the relative proportions of 20:4 (n-6) and 20:5 (n-3) ranged from 1.7–5.4% and 3.4–5.9% TFA respectively. Cultures aerated with 5% CO2 attained the highest biomass (97 mg AFDW L−1) and yield of 20:5 (n-3) (0.34 mg L−1).

Cultivation and carrageenan yield and quality of Kappaphycus alvarezii in the waters of Vietnam

Abstract: The carrageenan-producing red algaKappaphycus alvarezii (Doty) Doty was brought to Vietnam from Japan in 1993. Branch fragments of this species were cultivated in a pond, lagoon, inlet and offshore in Vietnam for the first time. The best daily growth rate (DGR) of plants grown in the lagoon area attained 9–11 % day−1 in May to June (cold season). The water temperature and salinity in this area ranged from 27.2–32.4 °C and 31.4–33.7 °C, respectively. DGR of plants grown in the inlet ranged from 7 to 9% day−1 in June. Grazing by fish has been observed to occur in this area. The DGR of plants grown in the pond ranged from 5–6% in January–July, but decreased to less than 4% day−1 in August (hot season).

In situ monitoring of chlorophyll fluorescence to assess the synergistic effect of low temperature and high irradiance stresses in Spirulina cultures grown outdoors in photobioreactors

Abstract: A chlorophyll fluorescence technique was applied to an in situ study on the effects of low temperature and high light stresses on Spirulina cultures grown outdoors in controlled tubular photobioreactors at high (1.1 g L- 1 ) and low (0.44 g L -1 ) biomass concentrations. Diurnal changes in PSII photochemistry (F v /F m ) after 15 min of darkness, or in the light (dF/F' m ), and non-photochemical (qN) quenching were measured using a portable, pulse-amplitude-modulated fluorometer. The depression of the F v /F m ratio of Spirulina cultures grown outdoors at 25°C (i.e. 10°C below optimum for growth) and 0.44 g L -1 , reached 30% at the middle of the day. At the same time of the day the dF/F' m ratio showed a reduction of up to 52%. The depression of both F v /F m and dF/F' m was lower in the cultures grown at 1.1 g L -1 . Photoinhibition reduced the daily productivity of the culture grown at 0.44 g L -1 and 25°C by 33% with respect to that grown at 35°C. Changes in the growth yields of the cultures grown under different temperatures and growth rates correlate well with analogous changes in photon yield (dF/F' m ). Simple measurements of photochemical yield (F v /F m ) can be used to test the physiological status of Spirulina cultures. The results indicate that the saturating pulse fluorescence technique, when used in situ, is a powerful tool for assessment of the photosynthetic characteristics of outdoor cultures of Spirulina.

Role of light and photosynthesis on the acclimation process of the cyanobacterium Spirulina platensis to salinity stress

Abstract: The response ofSpirulina platensis cells to salinity stress was studied. Once adapted to the higher osmoticum, photosynthetic parameters such as the maximum rate of photosynthesis under saturating irradiance (Pmax) and the initial slope of the P-I curve (α) are reduced by 15% and 25% in 0.5 M NaCl grown cells, respectively. Salt-adapted cells have a modified biochemical composition; reduced protein and chlorophyll content, and an increased level of carbohydrates. The reduction in the photosynthetic capacity of the salt-adaptedSpirulina cells reflects a lower ability to utilize light energy and results in an increase in the susceptibility of the stressed cells to photoinhibition. This conclusion is supported by the finding that cultures exposed to salt stress show not only a decrease in growth rate (μ), but lose the ability to respond to increased irradiance with an increase in growth. The use of variable fluorescence as a fast and reliable measurement to follow the changes in PSII of salt-stressesSpirulina cells enables following the early events of salinity shock. It indicates that as soon as the cells are exposed to salt, a protection mechanism is induced. This mechanism does not require any protein synthesis and may take place even in the dark, though at somewhat reduced effectiveness. The significance of the result in providing a better understanding of the interaction between two environmental stresses — light and salinity — and their application in the outdoor mass cultivation ofSpirulina are discussed.

An investigation of the heterotrophic culture of the green alga Tetraselmis

Abstract: The marine PrasinophyteTetraselmis may be cultured under both mixotrophic (photoheterotrophic) and heterotrophic conditions. The growth rate was slightly lower, and pigment levels and lipid composition were radically affected on heterotrophic culture in 1 L fermenters. Total chlorophyll levels of dark grown cultures were less than 1% of those observed in mixotrophically grown cells, the chlorophylla : b ratio also decreased as did the carotenoid content. In addition, the total amounts of lipids including polyunsaturated fatty-acids were also lower in heterotrophically cultured cells: 6.4 mg g−1 (dried alga) and 0.35 mg g−1 (dried alga); as compared to 37.1 mg g−1 (dried alga) and 18.5 mg g−1 (dried alga), for cells grown in the light. However, gross morphology and final yield (>16 g l−1) were relatively unaffected. The algae produced were spray-dried and tested for their suitability as an aquaculture feed.

Relationship between substrate inhibition and maintenance energy of Chlamydomonas reinhardtii in heterotrophic culture

Abstract: The relationship between substrate inhibition and maintenance energy ofChlamydomonas reinhardtii grown heterotrophically on acetate was investigated. At low acetate concentrations ( 0.4 g l−1), inhibition of cell growth occurred, in which m became variable and dependent on the acetate concentration. A simple mathematical model was proposed to predict the actual maintenance energy coefficient m in the inhibited cultures and experimentally validated.

Productivity analysis of outdoor chemostat culture in tubular air-lift photobioreactors

Abstract: Net productivity and biomass night losses in outdoor chemostat cultures ofPhaeodactylum tricornutum were analyzed in two tubular airlift photobioreactors at different dilution rates, photobioreactor surface/volume ratios and incident solar irradiance. In addition, an approximate model for the estimation of light profile and average irradiance inside outdoor tubular photobioreactors was proposed. In both photobioreactors, biomass productivity increased with dilution rate and daily incident solar radiation except at the highest incident solar irradiances and dilution rates, when photoinhibition effect was observed in the middle of the day. Variation of estimated average irradiance vs mean incident irradiance showed two effects: first, the outdoor cultures are adapted to average irradiance, and second, simultaneous photolimitation and photoinhibition took place at all assayed culture conditions, the extent of this phenomena being a function of the (incident)1 irradiance and light regime inside the culture. Productivity ranged between 0.50 and 2.04 g L−1 d−1 in the tubular photobioreactor with the lower surface/volume ratio (S/V = 77.5 m−1) and between 1.08 and 2.76 g L−1 d−1 in the other (S/V = 122.0 m−1). The optimum dilution rate was 0.040 h−1 in both reactors. Night-time biomass losses were a function of the average irradiance inside the culture, being lower in TPB0.03 than TPB0.06, due to a better light regime in the first. In both photobioreactors, biomass night losses strongly decreased when the photoinhibition effect was pronounced. However, net biomass productivity also decreased due to lower biomass generation during the day. Thus, optimum culture conditions were obtained when photolimitation and photoinhibition were balanced.

Influence of ammonium-N pulse concentrations and frequency, tank condition and nitrogen starvation on growth rate and biochemical composition of Gracilaria gracilis

Abstract: The growth rate ofGracilaria gracilis maintained in tanks at an abalone farm near Port Elizabeth, South Africa, was examined under various tank conditions and NH4-N pulse frequencies and concentrations. This was accompanied by analyses of the components of the internal nitrogen pool. A maximum growth rate of ca. 35% wk−1 was obtained at 1200 μM NH4-N. The alga was able to grow at non-nitrogen limited rates using only internal stored nitrogen to sustain growth for one week before the growth rate decreased to ca. 17% per week. NH4-N pulse frequency did not affect growth rate but one pulse per week led to a marked decrease in total-N, protein, phycoerythrin and chlorophyll-a content. An increase in pulse frequency to two pulses per week doubled the protein content from 2.351 ± 0.143 to 4.453 ± 0.090% (per unit dry mass). Carbohydrate content was inversely related to nitrogen storage. The growth rate in fouled tanks was always lower than in clean tanks. It seems likely that seaweeds and diatoms colonising the tank sides reduced light reflected off the inside of a tank, thereby reducing the growth rate.

Gram-scale purification of eicosapentaenoic acid (EPA, 20:5n-3) from wet Phaeodactylum tricornutum UTEX 640 biomass

Abstract: Eicosapentaenoic acid (EPA, 20:5n-3) was obtained from the microalgaPhaeodactylum tricornutum following a three-step process: fatty acid extraction by direct saponification of wet biomass, polyunsaturated fatty acid (PUFA) concentration by formation of urea inclusion compounds and EPA isolation by preparative HPLC. Direct saponification of wet biomass was carried out with KOH-ethanol (96% v:v) (1 h, 60 °C), extracting 91% of the EPA. PUFAs were concentrated by the urea method with an urea/fatty acid ratio of 4:1 at a crystallization temperature of 28 °C using methanol as the urea solvent. An EPA concentration ratio of 1.5 (55.2/36.3) and recovery of 79% were obtained. This PUFA concentrate was used to obtain 95.8% pure EPA by preparative HPLC, using a reverse-phase column (C18, 4.7 cm i.d. × 30 cm) and methanol-water (1% AcH) 80:20 w/w as the mobile phase. Ninety-seven per cent of EPA loaded was recovered and 70% EPA present in theP. tricornutum biomass was recovered in a highly pure form by means of this three-step downstream processing. In each of the HPLC preparative runs, 635 mg PUFA concentrate were loaded, obtaining 326 mg of a highly concentrated EPA fraction (2.46 g d−1). Finally, a preliminary cost statement has been calculated.

DSP toxin contents in Dinophysis fortii and scallops collected at Mutsu Bay, Japan

Abstract: Cell densities of toxic phytoplankton species responsible for diarrhetic shellfish poisoning (DSP) were monitored at a sampling site in Mutsu Bay, Japan, in 1995.Dinophysis fortii almost completely dominated the toxic phytoplankton community. Okadaic acid (OA) and dinophysistoxin-1 (DTX1) contents in bothD. fortii cells and midgut glands of scallops collected at the same sampling site were determined by HPLC — fluorometry. DTX1 was detected fromD. fortii and scallops. The contents of DTX1 inD. fortii changed markedly during the experimental periods (5–252 pg cell−1). The highest concentration of DTX1 in the midgut glands of scallops coincided with the period of relatively high cell densities ofD. fortii with the highest content of DTX1 (252 pg cell−1). The results demonstrate that toxin content in the cells is an important factor affecting the toxicity of shellfish.

Water treatment of land-based fish farm effluents by outdoor culture of marine diatoms

Abstract: The feasibility of using fish farm effluents was evaluated as a source of inorganic nutrients for mass production of marine diatoms. Batch cultures were conducted from May to July 1995 in 16-L outdoor rectangular tanks, homogenized by gentle aeration (0.2 L air L−1 h−1). The effluents from the two fish farms studied were both characterized by high concentrations of inorganic materials (NH4-N, PO4-;P, Si(OH)4-Si) and were shown to support production of marine diatoms. Moreover, periodic measurements of inorganic matter levels in the cultures showed that clearance was efficacious (90% in 3–5 days). Water purification efficiency and culture productivity were further increased through appropriate nutrient balancing. When effluents were limited in silicate, addition of Na2SiO3 induced a significant increase in both diatom biomass and nutrient removal efficiency. In this case, up to 720 000 cell mL−1 were produced dominated bySkeletonema costatum. By contrast, in effluents loaded with silicate, adjustment of the N:P:Si ratio by NH4-N and PO4-P supplementation then gave increased biomass production. In this case, the maximum cell density found was 450 000 cell mL−1, dominated byChaetoceros spp.

Annual variation in composition and in vitro anti-HIV-1 activity of the sulfated glucuronogalactan from Schizymenia dubyi (Rhodophyta, Gigartinales)

Abstract: An account is given of the annual variation in composition andin vitro anti-HIV-1 activity of the water-soluble sulfated glucuronogalactan fromSchizymenia dubyi collected in Sicily. No marked variation seasonal chemical or physico-chemical features was observed, with the exception of L-galactose residues and viscosity. Evaluation of the anti-HIV-1 effect of the polysaccharide indicated that syncitial formation and HIV-associated reverse transcriptasein vitro were completely suppressed at 5 μg ml−1 by alga collected during the summer/spring period. This high anti-HIV-1 activity corresponded with a decrease in L-galactose, viscosity and sulfate content of the polysaccharide.

Effect of blue-green light on growth rate and chemical composition of three diatoms

Abstract: The diatomsChaetoceros sp.,Skeletonema costatum andThalassiosira pseudonana were grown with different irradiances of white and of blue-green light, and with a mixture of blue-green plus 6.5 μmol m−2 s−1 of white light. Exponential growth rates were higher in mixed blue for the first two, whileT. pseudonana grew faster in white light but, in all cases, mean cell division rates did not differ with increasing irradiances. Harvesting in stationary, rather than in late exponential growth phase, resulted in higher protein contents forChaetoceros sp. andS. costatum, but forT. pseudonana the highest value was in the exponential phase. The highest protein content was in blue-green light for the three species and it increased with irradiance. As to other fractions, the three strains showed different responses, related to quality and quantity, as well as to culture ages.

Light acclimation and photoinhibition in three Spirulina platensis (cyanobacteria) isolates

Abstract: Three isolates ofSpirulina platensis (Norst) Geitler marked BP, P4P and Z19/2 were compared with respect to their response and acclimation capability to high photon flux densities (HPFD). Cultures exposed to HPFD (1500–3500 μmol photon m−2 s−1) exhibited a marked decrease in light-dependent O2 evolution rate. P4P was more sensitive to HPFD than the two other isolates. All three isolates recovered from photoinhibition when placed under low PFD. The BP isolate was able to recover also in the dark but to a lower extent and at a lower rate, while no recovery was observed in the other two isolates under dark conditions. No recovery was observed when protein synthesis was inhibited using chloramphenicol. Cultures grown at 200 μmol photon m−2 s−1 differed from cultures grown at 120 μmol photon m 2 s-1 by their lower maximal photosynthetic rate (P max ) and higher light saturation (I k ) value, while being more resistant to HPFD stress. The ability ofSpirulina isolates to acclimate and withstand HPFD may provide useful information for the selection of strains useful for outdoor mass cultivation.

Outdoor cultivation of Arthrospira platensis during autumn and winter in temperate climates

Abstract: Arthrospira (Spirulina) platensis M2 was grown outdoors in 50-mm diameter tubular reactors under the climatic conditions of central Italy (Florence) from September to December 1995 and in March 1996. Except for September, the cultures temperature was regulated. Mean productivities of 0.83, 0.44 and 0.61 g dry wt L−1 d−1 were achieved in autumn (September–October), winter (November–December) and March, respectively. In autumn and winter, the photosynthetic efficiency of the cultures and the degree of correlation between productivity and solar irradiance were significantly greater than in summer. The effect of cell density and aeration rate on productivity was evaluated in September. The productivity of cultures operated at high supra-optimal population density was about 30% less at high aeration rate (1.0 LL−1 min−1), and 50% less at standard aeration rate (0.17 LL−1 min−1), than that of control cultures kept at optimal population density and standard aeration rate. The reduction of productivity in high-density cultures was due to lower daylight output rates and higher night biomass losses (the latter were particularly relevant under standard aeration conditions). The main factor limiting productivity in closed reactors during autumn was the night temperature. Heating the cultures during daylight hours on sunny days did not cause any significant increase of the yields, since under sunlight the unheated cultures also reached the optimal temperature for growth early in the morning. On cloudy days, the day-time temperature of the unheated cultures remained well below the optimum, however this had only a limited effect on productivity since algal growth was mainly light-limited.

Gracilaria conferta and its epiphytes: 3. Allelopathic inhibition of the red seaweed byUlva cf.lactuca

Abstract: In a previous study (Svirski et al., 1993), it was found that growth inhibition ofGracilaria spp., when cultured in the presence ofUlva cf.lactuca, was not due to shading or nutrient depletion, but seemed to be caused by competition for inorganic carbon or some type of allelopathy. In the present study, we attempted to differentiate between these two possible influences by (1) growing the two algae in biculture under various conditions, but keeping inorganic carbon levels constant and measuring net photosynthesis, respiration and growth rates, and by (2) measuring growth rates ofGracilaria spp. in the presence of extracts derived from media previously used to growUlva cf.lactuca.