Effects of the herbivorous minnow,southern redbelly dace (<Emphasis Type="Italic">Phoxinus erythrogaster</Emphasis>), on stream productivity and ecosystem structure

We used field and mesocosm experiments to measure effects of southern redbelly dace (Phoxinus erythrogaster), a grazing minnow, on stream ecosystem structure and function. Ecosystem structure was quantified as algal filament length, algal biomass, size distribution of particulate organic matter (POM), algal assemblage structure, and invertebrate assemblage structure, whereas ecosystem function was based on gross and net primary productivity. Our experiments showed that moderate densities of Phoxinus temporarily reduced mean algal filament length and mean size of POM relative to fishless controls. However, there was no detectable effect on algal biomass or ecosystem primary productivity. Several factors could explain the lack of effect of Phoxinus on primary productivity including increased algal production efficiency in grazed treatments or increased grazing by other organisms in fishless treatments. The inability of Phoxinus to reduce algal biomass and system productivity contrasts with experimental results based on other grazing minnows, such as the central stoneroller (Campostoma anomalum), and questions the generality of grazer effects in stream ecosystems. However, environmental venue and the spatial and temporal scale of ecosystem measurements can greatly influence the outcome of these experiments. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. The experiments described herein comply with the current laws of the country in which the experiments were performed.     

Flocculation of microalgae using cationic starch

Due to their small size and low concentration in the culture medium, cost-efficient harvesting of microalgae is a major challenge. We evaluated the potential of cationic starch as a flocculant for harvesting microalgae using jar test experiments. Cationic starch was an efficient flocculant for freshwater (Parachlorella, Scenedesmus) but not for marine microalgae (Phaeodactylum, Nannochloropsis). At high cationic starch doses, dispersion restabilization was observed. The required cationic starch dose to induce flocculation increased linearly with the initial algal biomass concentration. Of the two commercial cationic starch flocculants tested, Greenfloc 120 (used in wastewater treatment) was more efficient than Cargill C*Bond HR 35.849 (used in paper manufacturing). For flocculation of Parachlorella using Greenfloc 120, the cationic starch to algal biomass ratio required to flocculate 80% of algal biomass was 0.1. For Scenedesmus, a lower dose was required (ratio 0.03). Flocculation of Parachlorella using Greenfloc 120 was independent of pH in the pH range of 5 to 10. Measurements of the maximum quantum yield of PSII suggest that Greenfloc 120 cationic starch was not toxic to Parachlorella. Cationic starch may be used as an efficient, nontoxic, cost-effective, and widely available flocculant for harvesting microalgal biomass.     

Effect of nitrogen regime on antioxidant parameters of selected prokaryotic and eukaryotic microalgal species

Nitrogen is a critical element for algal growth and shifting its concentration above or below the optimum concentration may have a deleterious effect on algal cells. Antioxidants are one of the important factors that protect algal cells from stresses, e.g., nitrogen stress. The purpose of this study was to evaluate the biomass, pigments, antioxidant compounds and activities of two algal species, Arthrospira platensis (prokaryotic Cyanophyta) and Pseudochlorella pringsheimii (eukaryotic Chlorophyta) under hypo- and hyper-nitrogen concentrations. In general, the increase in the nitrogen concentrations of the nutrient medium (75 and 6–18 mM for A. platensis and P. pringsheimii, respectively) led to an increase in the biomass yield, pigments and other antioxidant contents. However, this increment was reversed by further N additions. The data showed that the prokaryotic alga (A. platensis) can grow at relatively hyper-nitrogen concentrations rather than the eukaryotic one (P. pringsheimii). The antioxidant enzyme activities for the both species were significantly stimulated with the relatively lower nitrogen concentrations, while increasing the N concentrations in the media decreased the enzyme activities. Despite the superiority of A. platensis as a potent antioxidants source, both algae showed high antioxidant levels compared to the synthetic antioxidant marker (butylated hydroxytoluene, BHT).     

COMBINED EFFECTS OF ULTRAVIOLET RADIATION AND TEMPERATURE ON MORPHOLOGY,PHOTOSYNTHESIS, AND DNA OF ARTHROSPIRA (SPIRULINA) PLATENSIS (CYANOPHYTA)1

Natural levels of solar UVR were shown to break and alter the spiral structure of Arthrospira (Spirulina) platensis (Nordst.) Gomont during winter. However, this phenomenon was not observed during summer at temperatures of ～30°C. Since little has been documented on the interactive effects of solar UV radiation (UVR; 280–400 nm) and temperature on cyanobacteria, the morphology, photosynthesis, and DNA damage of A. platensis were examined using two radiation treatments (PAR [400–700 nm] and PAB [PAR + UV‐A + UV‐B: 280–700]), three temperatures (15, 22, and 30°C), and three biomass concentrations (100, 160, and 240 mg dwt [dry weight] · L^?1). UVR caused a breakage of the spiral structure at 15°C and 22°C, but not at 30°C. High PAR levels also induced a significant breakage at 15°C and 22°C, but only at low biomass densities, and to lesser extent when compared with the PAB treatment. A. platensis was able to alter its spiral structure by increasing helix tightness at the highest temperature tested. The photochemical efficiency was depressed to undetectable levels at 15°C but was relatively high at 30°C even under the treatment with UVR in 8 h. At 30°C, UVR led to 93%–97% less DNA damage when compared with 15°C after 8 h of exposure. UV‐absorbing compounds were determined as negligible at all light and temperature combinations. The possible mechanisms for the temperature‐dependent effects of UVR on this organism are discussed in this paper.     

Breeding and characterization of amino acid-analogue-resistant mutants of Arthrospira platensis

To obtain amino acid-analogue-resistant mutants the wild strain A9 of Arthrospira platensis was mutated by ethylmethane sulfonate (EMS). Mutagenic effects of strain A9 by EMS were studied. The experimental results indicated that the survival rate curve of strain A9 took a typical “exponential shape” with lethal dosage of EMS being 1 %. The survival of A9 strain was 13.2 % when treated with 0.4 % of EMS, and the resistant mutation rates to two amino acid analogues, ρ-fluorophenylalanine (FPA) and L-canavanine sulphate (CS), were greatly increased with the highest rates being at 4.9 × 10^?4 and 3.24 × 10^?4, respectively. By repeated screening, two stable mutants resistant to amino acid analogues, A9f resistant to FPA and A9c resistant to CS, were obtained. Resistances of the two mutants to corresponding amino acid-analogues were both significantly increased. Compared with their parent strain A9, A9f appeared larger than A9 performance in filament diameter, spiral diameter, spiral pitch, filament length and spiral number, and A9c showed much longer length and spiral pitch than those of the initial strain. Analysis results on amino acids compositions and contents showed that both two mutants accumulated quite higher concentration of amino acids in cells. The two mutants might be excellent high amino acids producing strain. By this means two useful mutants with stable genetic makers for further genetic study of A. platensis were obtained, which laid a good foundation for further study on the transformation of A. platensis.     

Harvesting of Aphanizomenon flos-aquae Ralfs ex Born. & Flah. var. flos-aquae (Cyanobacteria) from Klamath Lake for human dietary use

In western cultures, certain cyanobacteria have beenan accepted source of microalgal biomass for food forabout 30 years, in particular Spirulina(Arthrospira) platensis and S. maxima. Beginning in the early 1980s, another species, Aphanizomenon flos-aquae was adopted for similaruses. This is harvested from Upper Klamath Lake, thelargest freshwater lake system in Oregon. In 1998 theannual commercial production of Aphanizomenonflos-aquae was about 1 × 10⁶ kg. Since thisspecies is not cultured like Spirulina inoutdoor ponds or raceways, it requires very differentprocedures for harvesting and processing. These arereviewed here and include extensive off-lake screensor on-lake barges, which dewater and concentrate thecells. Other procedures, such as those for removal ofdetritus and mineral materials, and those formonitoring and reducing the amounts of certaincontaminant cyanobacteria, which can producecyanotoxins, have also become important in qualitycontrol and marketing.     

Effective biomass harvesting of marine diatom Chaetoceros muelleri by chitosan-induced flocculation,preservation of biomass,and recycling of culture medium for aquaculture feed application

Microalgae are a promising new source of biomass; however, large-scale economical harvesting of microalgal biomass is a major technological and economic challenge, limiting the commercial production of microalgal biomass for high-value compounds. In this study, the cationic polymer chitosan was used for the harvesting of the marine diatom Chaetoceros muelleri. Natural flocculation, and pH and chitosan-induced flocculation were studied in detail. The effects of flocculant dosage, culture pH, initial biomass concentration, and sedimentation time were investigated on biomass recovery. The results showed that flocculation efficiency can reach > 99% with an optimum dosage of chitosan (80 mg L^?1) at pH 9.6 and settling time of 40 minutes for biomass concentration from 0.2 to 1.2 g L^?1. The reusability of the recycled water, preservation of biomass after harvesting, and cost of the harvesting process were evaluated. The results showed that the chitosan-induced flocculation offers an efficient, cost-effective, rapid, and sustainable harvesting method for C. muelleri biomass for food and feed applications in aquaculture.

     

Growth and amino acid contents of<Emphasis Type="Italic">Spirulina platensis</Emphasis> with different nitrogen sources

The growth and amino acid contents of the cyanobacterium,Spirulina platensis strain NIES 46, were investigated using ammonium, nitrate, nitrite, or urea as the sole nitrogen source in a batch culture. Chlorophylla concentration was highest at 2,096 μg/L in the nitrate group after 10 days of cultivation, while the dry weight ofS. platensis was highest at 4.5 g/L in the ammonium group after 30 days of cultivation. The total amino acid content was highest at 174 mg/g dry weight ofS. platensis in the urea group at the end of the cultivation period, yet the amino acid patterns forS. platensis were similar for all the experimental groups. Therefore, it seemed that the growth and amino acid composition ofS. platensis varied depending on the type of nitrogen sources, while the amino acid patterns were not changed. Also, the most efficient harvesting time forS. platensis seemed to be approximately 10 days after cultivation.     

Growth of microalgae Botryococcus sp. in domestic wastewater and application of statistical analysis for the optimization of flocculation using alum and chitosan

Microalga biomass has been recognized as a sustainable bio-product to replace terrestrial biomass in biofuel production. The microalga industry has high operating costs, specifically on harvesting and biomass recovery. Therefore, the development of an efficient harvesting method is crucial to the minimization of production cost. A statistical analysis through response surface methodology was used to investigate the optimization of harvesting efficiency using alum and chitosan as a coagulant. Growth rate and biomass productivity were also determined. This research revealed that the harvesting efficiency using alum was 99.3%, with optimum dosage and pH of 177.74 mg L^?1 and 8.24, respectively. Chitosan achieved 94.2% biomass recovery at an optimal dosage of 169.95 mg L^?1 at pH of 12. Moreover, Botryococcus sp. achieved the maximum growth of 0.7551 µ_max d^?1, with an average total biomass productivity of 9.81 mg L^?1?d^?1 in domestic wastewater. Overall, this study shows that both alum and chitosan coagulants have great potential for efficient microalgal biomass recovery. It suggests that domestic wastewater as a potential growth medium for the large-scale production of microalga biomass.     

The consumption and utilization of the spiral blue-green algae Spirulina platensis in artificial diets by the silkworm, Bombyx mori

The consumption and utilization of various concentrations of the spiral blue-green algae, Spirulina platensis (Nordst.) Geitl., by the fourth-instar larvae of the silkworm, Bombyx mori L., was studied by incorporation into an artificial diet. The silkworms ingested more food on the low algal-powder diets, whereas they digested more efficiently on the high algal levels. The larvae fed on diets containing 30–40% algae had the shortest larval duration compared to those on low algal-powder diets. The freeze-dried powder of S. platensis is well utilized by B. mori larvae when added to artificial diets at levels between 15% and 30%, although the high algal content at 40% was slightly better for the efficiency of conversion of ingested diet into body substance (E.C.I.) and the cocoon production. However, analysis of the protein content in feces indicated an excess of the algal powder at 40%. Measurements of data on the food consumption and utilization in this study proposed that this spiral alga is dietetically utilizable as a protein source for rearing the silkworm in smaller quantities than on a soybean meal.

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Resúmé La consommation et l'utilisation de différentes concentrations de Spirulina platensis par les chenilles de 4ème stade de Bombyx mori, ont été étudiées par incorporation dans un aliment artificiel. Les vers à soie ont ingéré plus d'aliment avec les régimes à faible concentration en algue, tandis qu'ils ont digéré plus efficacement les régimes à haute concentration d'algue. Les chenilles alimentées sur des régimes contenant 30 à 40% d'algue ont eu un développement larvaire plus bref que celles alimentées sur des régimes à faible concentration. La poudre congelée et séchée de S. platensis incorporée aux taux de 15 à 30% dans le régime artificiel est bien utilisée par les chenilles de B. mori, quoiqu'une teneur de 40% soit légèrement meilleure pour l'efficacité de conversion de l'aliment en matière vivante (E.C.I.) et la production de cocons. Cependant, l'analyse du contenu protéique dans les excréments révélait un excès de poudre d'algue à 40%. L'analyse des données au cours de cette étude, sur la consommation et l'utilisation des aliments, montre que S. platensis est utilisable diét étiquement en plus petite quantité que la farine de soja comme source de protéines pour l'élevage du ver à soie.

     

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

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.Author for correspondence     

Effect of Spirulina platensis biomass on the growth of lactic acid bacteria in milk

The stimulatory effect of aqueous suspensions of Spirulina platensis dry biomass extracted at pH 6.8 and 5.5 was studied on four lactic acid bacteria (LAB) grown in milk. The addition of dry S. platensis to milk (6 mg/ml) stimulated growth of Lactococcus lactis by 27%. The growth of other strains was also promoted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of 24-epibrassinolide on biomass, growth and free proline concentration in Spirulina platensis (Cyanophyta) under NaCl stress

In this study, biomass, growth and free proline concentration were investigated in Spirulina platensis treated with different concentrations of NaCl (50, 100, 150, and 200 mM) and 24-epibrassinolide (24-epiBL) hormone (0.5, 1.0, and 3.0 μM) over 5 days. As a result of analysing the cultures under salinity stress, it was determined that biomass and growth rate decreased significantly, while proline concentration increased considerably under salinity stress. The increase in the concentration of proline suggests a role in response to NaCl stress. Among the cultures treated with different concentrations of 24-epiBL, maximum growth was determined at the cultures at 1.0 μM 24-epiBL. Algal growth was also greater at the 0.5 and 3.0 μM concentrations of 24-epiBL with respect to control cultures. With respect to control, 24-epiBL affected growth rate and biomass positively, but proline concentration did not change. Among the cultures supplied with different combinations of NaCl and 24-epiBL, growth rate increased in 150/0.5 and 150/3.0 mM/μM concentrations, but was maximal for the culture containing 150/1.0 mM/μM combination. The increase in algal growth suggests a role for 24-epiBL in partially alleviated to NaCl stress. These results suggest that 24-epiBL may have a protective role for S. platensis reducing the inhibitor effects of salinity stress.     

Biomass composition of <Emphasis Type="Italic">Arthrospira platensis</Emphasis> during cultivation on industrial process water and harvesting

Microalgae have the ability to utilize nutrients from wastewater and use it for biomass production. The effluent from a biogas process was tested as a nutrient source for blue-green microalga Arthrospira platensis cultivation and compared with conventional synthetic medium. Cultivation was carried out in four different concentrations of industrial process water (25, 50, 75, and 100%). The biomass was then harvested by microfiltration, and centrifugation followed by freeze drying. Variations in biomass composition were studied, in order to investigate effects of industrial process water on A. platensis over 30 days of cultivation. Applied harvesting techniques were evaluated for their effect on physiochemical properties of the biomass. Arthrospira platensis was able to grow in all tested wastewater concentrations except 100%, however, increase of wastewater concentration in medium resulted in a decreased growth rate. Partial substitution of synthetic Zarrouk medium with 25% of wastewater showed no adverse effect on chemical composition of the biomass including high protein content (45–58% dry weight) and favorable fatty acid composition (42–45% PUFAs of total fatty acids). Evaluation by optical microscopy showed that microfiltration caused cell rupture at the moderate level while centrifugation had more severe effect on A. platensis. Effect of centrifugal forces and shear stress on A. platensis cells was confirmed by detecting lower lipid content in samples after applying both microfiltration and centrifugation due to cell content leakage.     

Conversion of NaHCO3 to Na2CO3 with a growth of Arthrospira platensis cells in 660 m2 raceway ponds with a CO2 bicarbonation absorber

The weight ratio of Na₂CO₃/NaHCO₃ was investigated in order to improve microalgal productivity in large-scale industrial operations by converting NaHCO₃ to Na₂CO₃ with a growth of Arthrospira platensis cells in 660 m² raceway ponds. Two microalgal cultivation systems with a NaHCO₃ by-product (SPBP) and a CO₂ bicarbonation absorber (CBAP) were firstly thoroughly introduced. There was a 13.3% decrease in the initial weight ratio of Na₂CO₃/NaHCO₃ resulting in a 25.3% increase in the biomass growth rate with CBAP, compared to that of SPBP. Increased sunlight intensity, solution temperature and pH all resulted in both a higher absorbance and release, thereby increasing the weight ratio of Na₂CO₃/NaHCO₃ during the growth of A. platensis. The biomass growth rate was peaked at 39.9 g m⁻² day⁻¹ when the weight ratio of Na₂CO₃/NaHCO₃ was 3.7. Correspondingly, the cell pigments (chlorophyll a and carotenoid) and trichome size (helix pitch and trichome length) reached to a maximum state of 8.47 mg l⁻¹, 762 μg l⁻¹, 57 and 613 μm under the CBAP system.     

Modelling of Spirulina platensis growth in fresh water using response surface methodology

The influence of nutrient addition on the growth rate of Spirulina platensis in the Mangueira Lagoon water was studied in order to investigate the feasibility of using this water for biomass production. The addition of urea and sodium bicarbonate was studied through surface response methodology, over concentration ranges from 0.0 to 0.01170 M, and 0.0–19.70 gl^–1 respectively. The growth of Spirulina platensis in Mangueira Lagoon water with no addition of nutrients was carried out and compared with the biomass growth after nutrient addition. The results indicated that the optimal level of nutrients was 0.00585 M urea and without the addition of sodium bicarbonate. The biomass concentration was 1.4 gl^–1 in 780 h of cultivation and the doubling time (t _d) was 3.85 days. In 300 h, the biomass concentration in the medium without nutrient addition was 0.9 gl^–1, with a doubling time of 3.80 days.     

Root plasticity in Mediterranean herbaceous species

Abstract

Root plasticity has been largely studied on herbaceous species of north European temperate flora and is defined as the ratio between root depth in dry soils and root depth in wet soils. In summer dry habitats such as Mediterranean environments, the soil water deficit is a common feature to which root systems of plant species should adapt to improve their ecological efficiency. The aim of this study was to compare root plasticity in annual Mediterranean species that regenerate exclusively from seeds, and herbaceous perennial Mediterranean species that use dual regeneration strategies. Root plasticity of ten herbaceous species, six perennials and four annuals, was compared in this study. The annuals species studied occur in lowland Mediterranean grasslands referred to Tuberarietea guttatae class (Dasypyrum villosum, Lophochloa pubescens, Ornithopus compressus, Rumex bucephalophorus), while the perennial species occur in montane sub-Mediterranean grasslands referred to Festuco brometea (Bromus erectus, Festuca ovina., Lotus corniculatus., Minuartia verna, Sanguisorba minor, Thymus longicaulis). The examined species were subjected to water stress according to standard methods applied in comparative ecology, i.e., half of the seedlings of each species received 20 ml de-ionized water daily for three weeks, while the other half did not. After seedling harvesting the following parameters were analysed: (i) total root length; (ii) root length in the first 10 cm of soil; (iii) shoot height; (iv) root biomass in the first 10 cm of soil; (v) shoot biomass; (vi) shoot and root plasticity. Results show that root plasticity increased significantly in dual-regenerator sub-Mediterranean mountain species.     

Anti‐angiogenic effects of the blue‐green alga Arthrospira platensis on pancreatic cancer

Arthrospira platensis, a blue‐green alga, is a popular nutraceutical substance having potent antioxidant properties with potential anti‐carcinogenic activities. The aim of our study was to assess the possible anti‐angiogenic effects of A platensis in an experimental model of pancreatic cancer. The effects of an A platensis extract were investigated on human pancreatic cancer cells (PA‐TU‐8902) and immortalized endothelial‐like cells (Ea.hy926). PA‐TU‐8902 pancreatic tumours xenografted to athymic mice were also examined. In vitro migration and invasiveness assays were performed on the tested cells. Multiple angiogenic factors and signalling pathways were analysed in the epithelial, endothelial and cancer cells, and tumour tissue. The A platensis extract exerted inhibitory effects on both migration and invasion of pancreatic cancer as well as endothelial‐like cells. Tumours of mice treated with A platensis exhibited much lesser degrees of vascularization as measured by CD31 immunostaining (P = .004). Surprisingly, the VEGF‐A mRNA and protein expressions were up‐regulated in pancreatic cancer cells. A platensis inhibited ERK activation upstream of Raf and suppressed the expression of ERK‐regulated proteins. Treatment of pancreatic cancer with A platensis was associated with suppressive effects on migration and invasiveness with various anti‐angiogenic features, which might account for the anticancer effects of this blue‐green alga.     

A culture method for microalgal forms using two-tier vessel providing carbon-dioxide environment: studies on growth and carotenoid production

A culture method was developed for photoautotrophic culture of Haematococcus pluvialis, Chlorella vulgaris, Scenedesmus obliquus, Spirulina platensis, Nostoc and Stigonema in a two-tier flask consisting of nutrient media in the upper chamber and CO₂ generating buffer mixture (KHCO₃/K₂CO₃) in the lower chamber. The concentration of buffer mixture was varied to obtain desired levels of CO₂. CO₂ at 2.0% (v/v) level enhanced growth and chlorophyll content over control cultures (without CO₂ supplementation) in all microalgal species. Haematococcus pluvialis culture in BBM and KM1 media showed 6.71- and 2.07-fold increase in biomass yields with astaxanthin productivity at 7.26 and 7.48 mg l^–1 level respectively. CO₂ supplementation to C. vulgaris and S. obliquus cultures resulted in 5.97- and 7.30-folds increase in biomass with 2–3 fold increase in chlorophyll and carotenoid contents over their respective controls. Similarly 2–3 fold increase in chlorophyll and carotenoid contents were observed in Sp. platensis, Nostoc and Stigonema spp. This culture methodology will provide information on CO₂ requirement for growth of algae and metabolite production and also facilitates studies on the influence of light and temperature conditions.     

Microalgal system for treatment of effluent from poultry litter anaerobic digestion

The potential of mixotrophic microalgae to utilize poultry litter anaerobic digester (AD) effluent (PLDE) as nutritional growth medium was evaluated. Three algal strains viz. Chlorella minutissima, Chlorella sorokiniana and Scenedesmus bijuga and their consortium showed significant biomass productivity in 6% (v/v) concentration of PLDE in deionized water. Multiple booster dosage of PLDE supported better growth relative to a single dose PLDE. The maximum biomass productivity of 76 mg L⁻¹ d⁻¹ was recorded. The biomass was rich in protein (39% w/w) and carbohydrates (22%) while lipids (<10%) were low, making it most suitable as an animal feed supplement. The mixotrophic algae showed sustainable growth against variations in PLDE composition in different AD batches, thus proving to be a suitable candidate for large scale wastewater treatment with concomitant production of renewable biomass feedstock for animal feed and bioenergy applications.