Anabaena Circinalis Research Articles

EXPRESSION OF THE GEOSMIN SYNTHASE GENE IN THE CYANOBACTERIUM ANABAENA CIRCINALIS AWQC318(1).

The occurrence of taste and odor episodes attributed to geosmin continues to trouble water utilities worldwide, and only recently have advances been made in our fundamental understanding of the biochemical and genetic mechanisms responsible for the production of geosmin in microorganisms. For the first time, we have examined the expression of the geosmin synthase gene and corresponding geosmin production by Anabaena circinalis Rabenh. ex Bornet et Flahault AWQC318 under conditions of continuous light illumination and the removal of light as a stimulus and demonstrate that the expression of geosmin synthase appears to be constitutive under these conditions. The decrease in geosmin synthase transcription post maximum cell numbers and stationary phase suggests that a decrease in isoprenoid synthesis may occur before a decrease in the transcription of ribosomal units as the process of cell death is initiated.

Fate of toxic cyanobacterial cells and disinfection by-products formation after chlorination

Drinking water sources in many regions are subject to proliferation of toxic cyanobacteria (CB). Chlorination of source water containing toxic cyanobacterial cells for diverse treatment purposes might cause cell damage, toxin release and disinfection by-products (DBP) formation. There is limited information available on chlorination of different toxic CB cells and DBP formation potentials. This work: (1) determines the extent of lysis and toxins/taste and odor compound release in chlorinated natural water from CB cells (Anabaena circinalis, Microcystis aeruginosa, Cylindrospermopsis raciborskii, and Aphanizomenon issatsckenka) from laboratory cultures and natural blooms; (2) assesses the rates of oxidation of toxins by free chlorine under environmental conditions; (3) studies the DBP formation associated with the chlorination of CB cell suspensions. With chlorine exposure (CT) value of <4.0 mg min/L >60% cells lost viability causing toxin release. Cell membrane damage occurred faster than oxidation of released toxins. Kinetic analysis of the oxidation of toxins in natural water revealed significant differences in their susceptibility to chlorine, saxitoxins being the easiest to oxidize, followed by cylindrospermopsin and microcystin-LR. Furthermore, concentrations of trihalomethanes and haloacetic acids (<40 μg/L) and N-nitrosodimethylamine (<10 ng/L) as chlorination by-products were lower than the guideline values even at the highest CT value (220 mg min/L). However, the DBP concentrations in environmental bloom conditions with very high cell numbers were over the guideline values.

Integrated membrane systems incorporating coagulation, activated carbon and ultrafiltration for the removal of toxic cyanobacterial metabolites from Anabaena circinalis

The use of integrated membrane systems (a train of treatment processes incorporating one or more membranes) is increasing globally as the technology is very effective for the production of high quality drinking water. In this investigation a laboratory scale integrated membrane system (IMS) featuring coagulation, powdered activated carbon (PAC) and ultrafiltration (UF) was investigated for the removal of an Australian strain of the cyanobacteria Anabaena circinalis and the cyanotoxin it produced. Three coagulants were compared, aluminium chlorohydrate (ACH), aluminium sulphate (alum) and an engineered aluminium coagulant referred to as high performance aluminium chlorohydrate (HPAC). PAC (Acticarb PS1000) was tested to determine adsorption of extracellular saxitoxin. Removal of A. circinalis cells was 100% by UF alone and the removal of cells prior to the membrane by coagulation reduced fouling attributed to algogenic organic material. Alum was the least efficient coagulant for removal of cells while ACH and HPAC were similar. Saxitoxin removal reached a maximum of 80% using ACH and PAC. The UF-IMS was challenged using a natural bloom of A. circinalis that occurred in the Myponga Reservoir in South Australia.

Preparation of Calibration Standards of N1-H Paralytic Shellfish Toxin Analogues by Large-Scale Culture of Cyanobacterium Anabaena circinalis (TA04)

Mouse bioassay is the official testing method to quantify paralytic shellfish toxins (PSTs) in bivalves. A number of alternative analytical methods have been reported. Some methods have been evaluated by a single laboratory validation. Among the different types of methods, chemical analyses are capable of identifying and quantifying the toxins, however a shortage of the necessary calibration standards hampers implementation of the chemical analyses in routine monitoring of PSTs in bivalves. In our present study, we studied preparation of major PST analogues as calibrants by large-scale cultivation of toxic freshwater cyanobacteria Anabaena circinalis TA04. The cells were steadily grown in 10 L bottle for 28 days. The primary N1-H toxins, C1/C2, were produced at a concentration of 1.3 ±0.1 μmol/L. The intracellular and extracellular toxins occupied 80% and 20%, respectively. Over 220 μmol of the toxins was obtained from approximately 200 L of the culture over six months, demonstrating that it is sufficient to prepare saxitoxin analogues. The toxins were chemically converted to six N1-H analogues. Preparation of the analogues was carried out at relatively high yields (50–90%). The results indicate that our preparation method is useful to produce N1-H toxins. In our present study, detailed conditions for preparation of one of the rare N1-H analogues, gonyautoxin-5, were investigated.

English

Cyanobacteria offer an economically and ecologically sound alternative to chemical fertilizers for realizing the ultimate goal of increased productivity, especially in rice cultivation. There is however, a growing concern about the adverse effects of indiscriminate use of chemical fertilizers on soil productivity and environmental quality. A comparative study between the NR activity and biomass of six Anabaena strains isolated from paddy field soils of Ganjam district in presence of pH, temperature, copper& molybdenum, NaNO 3, NH 4Cl, and Urea is being conducted to present a situation where NR activity and biomass may be affected under varied concentration. Maximum NR activity was observed in Anabaena sp. at pH 8.5 and 35 o C temperature while Anabaena circinalis showed minimum activity in same concentration. Biomass content was maximum in Anabaena variabilis at pH 8.5 where as at temperature 35 o C in Anabaena flos-aquae and minimum biomass observed in Anabaena iyengarii at same concentration. NR activity in relation to copper was maximum in Anabaena sp. at 2 �g/l while minimum in Anabaena circinalis at same concentration. At 0.5µg/l molybdenum content in the culture medium showed maximum NR activity in Anabaena sp and reduced in all strains with increase of concentration. Anabaena flos-aquae showed minimum NR activity at 0.1mM concentration of NaNO 3 while Anabaena circinalis showed minimum NR activity at same concentration of NH 4Cl. The NR activity was observed minimum at 3mM concentration of Urea in A. cylindrica . The activity of NR and biomass in all the strains was influenced by external NH 4 - and NO 3

DISTURBANCES IN THE SIZE OF VARIOUS METABOLIC POOLS OF SOME ISOLATED SOIL ALGAL SPECIES IN RESPONSE TO HEAVY METAL TOXICITY

The growth and some metabolic activities of the five species namely Chlamydomonas reinhardtii (Dang), Chlorococcum humicola (Nag), Scenedesmus obliquus (Turp) Kutz (green algae) and Anabaena circinalis (Rabh.) and Wollea saccata (Wollea Bornet and Flahault) (Blue-green algae) isolated from soil at Assiut, Egypt were investigated under various concentrations of Cd2+, Ni2+ and Pb2+. The growth of the C. reinhardtii, C. humicola and S. obliquus were inhibited by all used heavy metals. The highest inhibitory effect was exerted by Ni2+ or Cd2+, while the lowest toxicity was exerted by Pb2+. However, the growth was enhanced by low and medium concentrations of Pb2+. The toxicity of heavy metals for C. reinhardtii, C. humicola, S. obliquus and W. saccata was as follows Ni2+ > Cd2+ > Pb2+. In case of A. circinalis the toxicity of heavy metal was as follows Cd2+ > Ni2+ > Pb2+. Soluble sugars, soluble protein, free amino acids and proline of all species, exhibited a high significant increase with all tested heavy metals supplemented. Insoluble carbohydrates, were generally lowered in various treatments, of heavy metals irrespective the test algae.

Release and Oxidation of Cell-Bound Saxitoxins during Chlorination of Anabaena circinalis Cells

Surface water sources are increasingly subject to proliferation of toxic cyanobacteria. Direct chlorination of source water containing toxic cyanobacterial cells for different treatment purposes might cause cell damage and toxin release. There is limited information available on chlorination of saxitoxins (STXs: saxitoxin, C-toxins, and gonyautoxins) produced by Anabaena circinalis. This work: (1) investigated the impact of chlorination on cell lysis and toxin/odor compound release in natural waters; (2) assessed the rates of chlorination of total STXs, and (3) estimated apparent rate constants for STX oxidation in ultrapure and natural waters. With a chlorine exposure (CT) value of 7.0 mg x min/L all cells lost viability causing toxin release. Cell-membrane damage occurred faster than released STXs oxidation. All saxitoxin and more than 95% of other STX analogues were subsequently oxidized. Kinetic analysis of the oxidation of STX analogues revealed significant differences in the susceptibility to chlorine, saxitoxin being the easiest to oxidize. Also, concentrations of trihalomethanes, haloacetic acids, and N-nitrosodimethylamine as chlorination byproducts were respectively <50 μg/L and 11 ng/L even at the highest CT value (50.3 mg x min/L).

Use of flow management to mitigate cyanobacterial blooms in the Lower Darling River, Australia

The growth of planktonic cyanobacteria in a weir pool on the Lower Darling River, Australia, downstream of the major regulated Menindee Lake system was examined. Blooms of the saxitoxin producing freshwater cyanobacterium Anabaena circinalis occurred for two summers out of four studied. Large cell numbers of other cyanobacteria including Aphanizomenon, Planktolyngbya and Merismopedia also occurred during the same summer periods as the Anabaena blooms. The growth events also coincided with periods of improved light climate. Flow releases from the regulated Menindee Lakes System were assessed for their ability to either suppress bloom development or to mitigate pre-existing blooms over this period. A discharge of 300 ML/day (flow velocity of 0.03 m/s) was found to be sufficient to prevent prolonged periods of persistent thermal stratification, which also suppressed the development of A. circinalis blooms. A flow release of 3000 ML/day was effective at removing an established cyanobacterial bloom, and total cyanobacterial numbers declined from over 100 000 to ,1000 cells/mL within a week. In two summers without blooms, higher flows and decreased light availability prevented the development of cyanobacterial blooms. Flow releases were effective at mitigating cyanobacterial growth through either the suppression of persistent thermal stratification or through dilution and translocation of cells. Greater discharges also increased turbidity, which diminished the growth of cyanobacteria through reduced light availability under the mixed conditions, which also reduced the ability for surface migration through buoyancy regulation. The volume of water required for different management strategies varied and is considered in terms of environmental allocations.

Phytoplanktonic Structure and Chemistry of the Water in the Monjolinho Reservoir (SP, Brazil) During a Cyanobacterial Bloom Episode

The composition of the phytoplankton and parameters of the water quality were studied in a tropical reservoir during cyanobacterial bloom episode. Samples were collected at two sites during October 2004. The phytoplankton community consisted of 69 taxa, distributed into 9 classes. Most taxa belonged to Cyanobacteria (17), Chlorophyceae (21), Bacillariophyceae (8), Conjugatophyceae (7), Dinophyceae (1), Chrysophyceae (4), Euglenophyceae (9), Cryptophyceae (1) and Xanthophyceae (1). Anabaena circinalis Rabenhorst ex Bornet et Flahault e Anabaena spiroides Klebahn were the dominant species. Statistical analyses revealed significant spatial variation (p &lt; 0.05) between sampling points only for N compounds and chlorophyll a. Most limnological variables analyzed showed no significant temporal variation (p &gt; 0.05). Cyanobacteria bloom was concomitant with the following environmental conditions, warm water temperatures (19 to 22 oC), periods of water column stability and high concentrations of N (724.9 μg.L-1) and P (90.9 μg.L-1) in the reservoir and NH4 as being the predominant nitrogen compounds. It is speculated that those conditions could play a role in the dominance of cyanobacteria.

Toxicity of cyanobacterial bloom in the eutrophic dam reservoir (Southeast Poland)

Cyanobacterial bloom was observed in a highly eutrophic dam reservoir, Zemborzycki, near Lublin (SE Poland) over a warm period in the year 2007. The water bloom consisted of several cyanobacterial taxa: Anabaena circinalis, Anabaena spiroides, Anabaena flos-aquae, Planktothrix agardhii, Aphanizomenon flos-aquae, Aphanizomenon gracile, and Microcystis flos-aquae. Anabaena spp., and Aphanizomenon spp., potential producers of neurotoxic anatoxin-a, quantitatively predominated in the studied bloom. High-performance liquid chromatography (HPLC) analysis of surface scum sampled during Anabaena circinalis domination revealed the presence of anatoxin-a at a high concentration (1,035.59 microg per liter of surface scum). At the same time, neither gas chromatography/mass spectrometry (GC/MS) nor microcystin enzyme-linked immunosorbent assay (ELISA) test showed the presence of other frequently found cyanotoxins, microcystins. Toxicity of cyanobacterial bloom was assessed by the crustacean acute toxicity test Daphtoxkit F pulex using Daphnia pulex, and by the chronic toxicity test Protoxkit F with a ciliate protozoan Tetrahymena thermophila. The crude extract of cyanobacterial scum showed high toxicity for Daphnia pulex, with 24-h median effective concentration (EC50) value of 90.3 microg/L of anatoxin-a, which corresponded to the cyanobacterial density in the scum of 1.01 g dry weight/L. For Tetrahymena thermophila, 24-h EC50 was lower, evaluated to be 60.48 microg/L of anatoxin-a, which corresponded to a cyanobacterial density of 0.68 g dry weight/L of the scum. On the basis of evaluated toxicity units, the cyanobacterial extract was classified at class IV toxicity, which means high toxic hazard.

Effect of chlorination on the cell integrity of two noxious cyanobacteria and their releases of odorants

The effect of chlorination on cell integrity and release of metabolites of two noxious cyanobacteria, a β-cyclocitral producer— Microcystis aeruginosa —and a geosmin producer— Anabaena circinalis —was investigated. Photos from a scanning electron microscope revealed that Microcystis cell surfaces were deformed after chlorination, and filamentary Anabaena cells were ruptured at the junction of vegetative cell units. Chlorination experiments indicated that both cyanobacteria are susceptible to attack by chlorine. A first-order decay model was used to simulate the cell-rupture kinetics during chlorination. Using laboratory cultures, the observed rate constants are 670–1,100 M−1 s−1 for M. aeruginosa , which are 1.3–5.0 times as large as those for A. circinalis . For unfiltered Microcystis -laden reservoir waters, a broader range of rate constants, 70–590 M−1 s−1, were obtained. The rate constant was reduced in more eutrophic water, due probably to the competition of chlorine with other cyanobacteria in water. Geosmin was rapidly released into water immediately after the Anabaena cells were ruptured. However, a portion of geosmin remained cell-bound. For Microcystis , the total β-cyclocitral concentration decreased quickly during chlorination in most cases. It is speculated that the enzymes leading to the formation of β-cyclocitral were inhibited by chlorine, thus causing a sudden reduction of β-cyclocitral in the system.

Population dynamics: seasonal variation of phytoplankton functional groups in brazilian reservoirs (Billings and Guarapiranga, São Paulo)

Phytoplankton may function as a 'sensor' of changes in aquatic environment and responds rapidly to such changes. In freshwaters, coexistence of species that have similar ecological requirements and show the same environmental requirements frequently occurs; such species groups are named functional groups. The use of phytoplankton functional groups to evaluate these changes has proven to be very useful and effective. Thus, the aim of this study was to evaluate the occurrence of functional groups of phytoplankton in two reservoirs (Billings and Guarapiranga) that supply water to millions of people in São Paulo city Metropolitan Area, southeastern Brazil. Surface water samples were collected monthly and physical, chemical and biological (quantitative and qualitative analyses of the phytoplankton) were performed. The highest biovolume (mm(3).L-1) of the descriptor species and functional groups were represented respectively by Anabaena circinalis Rabenh. (H1), Microcystis aeruginosa (Kützing) Kützing (L M/M) and Mougeotia sp. (T) in the Guarapiranga reservoir and Cylindrospermopsis raciborskii (Wolosz.) Seen. and Subba Raju (S N), Microcystis aeruginosa and M. panniformis Komárek et al. (L M/M), Planktothrix agardhii (Gom.) Anagn. and Komárek and P. cf. clathrata (Skuja) Anagn. and Komárek (S1) in the Billings reservoir. The environmental factors that most influenced the phytoplankton dynamics were water temperature, euphotic zone, turbidity, conductivity, pH, dissolved oxygen, nitrate and total phosphorous.

Changes in species composition during annual cyanobacterial dominance in a tropical reservoir: physical factors, nutrients and grazing effects

Trends in recent years have indicated that cyanobacterial blooms in tropical reservoirs are increasing in frequency, magnitude and geographical distribution. Funil Reservoir in south- eastern Brazil has experienced eutrophication in the recent decades, resulting in lasting and intense toxic cyanobacterial blooms. As input of nutrients is high during the year, the aim of the present study was to evaluate the role of other variables related to changes in cyanobacterial biomass and compo- sition. The dominant group found over the entire study period was Cyanobacteria (97% of total biomass), which contributed to low diversity. A shift of nitrogen-fixing (Anabaena circinalis and Cylindrospermopsis raciborskii) and non nitrogen-fixing (Microcystis aeruginosa) cyanobacteria was observed. Redundancy analysis indicated that physical factors such as temperature, changes in the mixing zone and light intensity were the main driving factors of the seasonal succession. Nitrogen- fixing cyanobacteria dominated in periods of low light in the deepest mixing zone, and also seemed to have experienced stronger grazing effects as the density of the large zooplankton group was related to cyanobacteria biomass. M. aeruginosa bloomed in warm stratified waters, high water levels and during months with more daylight, when the zooplankton density was drastically reduced. Although the long-standing dominance of cyanobacteria may be related to high nutrient availability, the present study showed that under high and constant input of nutrients, other factors, especially physical variables, present a more plausible explanation to promote changes in species composition.

Optimising water treatment practices for the removal of Anabaena circinalis and its associated metabolites, geosmin and saxitoxins

The cyanobacterium Anabaena circinalis has the ability to co-produce geosmin and saxitoxins, compounds which can compromise the quality of drinking water. This study provides pertinent information in optimising water treatment practices for the removal of geosmin and saxitoxins. In particular, it demonstrates that pre-oxidation using potassium permanganate could be applied at the head of water treatment plants without releasing intracellular geosmin and saxitoxins from A. circinalis. Furthermore, powdered activated carbon (PAC) was shown to be an effective treatment barrier for the removal of extracellular (dissolved) geosmin and saxitoxins, with similar adsorption trends of both compounds. The relative removal of the saxitoxins compared with geosmin was determined to be 0.84 +/- 0.27, which implies that saxitoxin removal with PAC can be estimated to be approximately 60 to 100% of the removal of geosmin under equivalent conditions. Chlorine was shown to be effective for the oxidation of the saxitoxins with CT values of approximately 30 mg min l(-1) required for greater than 90% destruction of the saxitoxins.

Origin of Saxitoxin Biosynthetic Genes in Cyanobacteria

BackgroundParalytic shellfish poisoning (PSP) is a potentially fatal syndrome associated with the consumption of shellfish that have accumulated saxitoxin (STX). STX is produced by microscopic marine dinoflagellate algae. Little is known about the origin and spread of saxitoxin genes in these under-studied eukaryotes. Fortuitously, some freshwater cyanobacteria also produce STX, providing an ideal model for studying its biosynthesis. Here we focus on saxitoxin-producing cyanobacteria and their non-toxic sisters to elucidate the origin of genes involved in the putative STX biosynthetic pathway.Methodology/Principal FindingsWe generated a draft genome assembly of the saxitoxin-producing (STX+) cyanobacterium Anabaena circinalis ACBU02 and searched for 26 candidate saxitoxin­genes (named sxtA to sxtZ) that were recently identified in the toxic strain Cylindrospermopsis raciborskii T3. We also generated a draft assembly of the non-toxic (STX−) sister Anabaena circinalis ACFR02 to aid the identification of saxitoxin-specific genes. Comparative phylogenomic analyses revealed that nine putative STX genes were horizontally transferred from non-cyanobacterial sources, whereas one key gene (sxtA) originated in STX+ cyanobacteria via two independent horizontal transfers followed by fusion. In total, of the 26 candidate saxitoxin-genes, 13 are of cyanobacterial provenance and are monophyletic among the STX+ taxa, four are shared amongst STX+ and STX-cyanobacteria, and the remaining nine genes are specific to STX+ cyanobacteria.Conclusions/SignificanceOur results provide evidence that the assembly of STX genes in ACBU02 involved multiple HGT events from different sources followed presumably by coordination of the expression of foreign and native genes in the common ancestor of STX+ cyanobacteria. The ability to produce saxitoxin was subsequently lost multiple independent times resulting in a nested relationship of STX+ and STX− strains among Anabaena circinalis strains.

FLORAÇÕES DE CIANOBACTÉRIAS TÓXICAS NO RESERVATÓRIO DO FUNIL: DINÂMICA SAZONAL E CONSEQÜÊNCIAS PARA O ZOOPLÂNCTON

The Funil water reservoir, located in the Paraiba do Sul River Valley in the municipality of Resende (Rio de Janeiro State, Brazil), has become eutrophic during the last two decades and undergone recurrent blooms of cyanobacteria. This study presents temporal series of physical, chemical and biological data from the reservoir encompassing an overall period of four years (from June/02 to March/06). Monthly, measurements of conductivity, transparency, temperature, pH, dissolved oxygen, and water samples for the analyses of nutrients (N and P), chlorophyll-a, phytoplankton and zooplankton composition and cyanotoxins in seston and in net plankton were performed. Toxicity tests with native and temperate cladocerans species were also performed. The results showed that the high input of N and P favored the persistent dominance of cyanobacteria. A temporal pattern was observed mainly related to changes in water temperature, characterizing two distinct periods: a warm-wet period with cyanobacterial bloom, and a cold-dry period with general reduced biomass. Cyanobacteria included potential hepatotoxins (microcystins) producers like Microcystis spp., and potential neurotoxins (saxitoxins) producers like Anabaena circinalis and Cylindrospermopsis raciborskii. In fact, elevated concentrations of microcystins and saxitoxins were found in the phytoplankton, and high levels of microcystins in the zooplankton, suggesting that these toxins may be transferred through the food chain. The toxicity tests revealed that the cyanobacterial blooms had toxic effects on cladocerans, causing death, reduction in the rate of population increase (r), and paralysis, in agreement with the mechanism of action of the cyanotoxins present.

Characterisation of the paralytic shellfish toxin biosynthesis gene clusters in Anabaena circinalis AWQC131C and Aphanizomenon sp. NH-5.

BackgroundSaxitoxin and its analogues collectively known as the paralytic shellfish toxins (PSTs) are neurotoxic alkaloids and are the cause of the syndrome named paralytic shellfish poisoning. PSTs are produced by a unique biosynthetic pathway, which involves reactions that are rare in microbial metabolic pathways. Nevertheless, distantly related organisms such as dinoflagellates and cyanobacteria appear to produce these toxins using the same pathway. Hypothesised explanations for such an unusual phylogenetic distribution of this shared uncommon metabolic pathway, include a polyphyletic origin, an involvement of symbiotic bacteria, and horizontal gene transfer.ResultsWe describe the identification, annotation and bioinformatic characterisation of the putative paralytic shellfish toxin biosynthesis clusters in an Australian isolate of Anabaena circinalis and an American isolate of Aphanizomenon sp., both members of the Nostocales. These putative PST gene clusters span approximately 28 kb and contain genes coding for the biosynthesis and export of the toxin. A putative insertion/excision site in the Australian Anabaena circinalis AWQC131C was identified, and the organization and evolution of the gene clusters are discussed. A biosynthetic pathway leading to the formation of saxitoxin and its analogues in these organisms is proposed.ConclusionThe PST biosynthesis gene cluster presents a mosaic structure, whereby genes have apparently transposed in segments of varying size, resulting in different gene arrangements in all three sxt clusters sequenced so far. The gene cluster organizational structure and sequence similarity seems to reflect the phylogeny of the producer organisms, indicating that the gene clusters have an ancient origin, or that their lateral transfer was also an ancient event. The knowledge we gain from the characterisation of the PST biosynthesis gene clusters, including the identity and sequence of the genes involved in the biosynthesis, may also afford the identification of these gene clusters in dinoflagellates, the cause of human mortalities and significant financial loss to the tourism and shellfish industries.

Limnological characteristics and trophic state of Paso de las Piedras Reservoir: An inland reservoir in Argentina

AbstractThe current trophic status of Paso de las Piedras Reservoir was evaluated by analysing different physicochemical, biological and environmental variables, in relation to its water quality, and application of two different classification criteria. Water quality sampling was conducted at four sampling sites from June 2004 to June 2005. During this study, 183 phytoplankton taxa were identified. The phytoplankton abundance exhibited a maximum of 368.037 × 103 cells.mL−1 in February 2005, and at least 1.133 × 103 cells.mL−1 in October 2004. An almost exclusive dominance of Cyanobacteria was observed between December 2004 and May 2005, the product of a large relative abundance of Anabaena circinalis and Microcystis natans which, together with other companions, were the reason for an algal bloom characterized by an average density of 133.05 × 103 cells.mL−1, and an average chlorophyll concentration of 28.7 mg.m−3. These study results indicate that the seasonal variations of physical, chemical and biological parameters in the waters of this reservoir were essentially a consequence of environmental and hydrological conditions in the dam area. In contrast, the spatial variations inside the lake were the result of the characteristics of the water inflow provided by its two main tributaries. The N:P ratio suggests neither nutrient is a limiting factor for maximum algal biomass in the lake, indicating that variations in the phytoplankton community structure, and development of phytoplankton blooms, would be more constrained by environmental and hydrological conditions than nutrient competition. The high concentration of measured nutrients could be attributed to the concurrence of various non‐point sources. The phytoplankton species richness was high, exhibiting values even higher than those mentioned in previous studies. Considering the two trophic classification systems, and based on total phosphorus data, the reservoir is classified within the hypertrophic category. In contrast, considering only the chlorophyll and turbidity data, the lake would be classified within the eutrophic category.

Effects of bacillamide and newly synthesized derivatives on the growth of cyanobacteria and microalgae cultures

The antialgal activity of newly synthesized bacillamides against several cyanobacteria and microalgae isolates was screened using a rapid 96-well microplate bioassay. Cultures were exposed to serial dilutions of each bacillamide derivative (0–160 μg mL−1) in the microplate wells and daily optical measurements were used to estimate growth over a 216 h period. Inhibition values (%) were calculated from the estimated growth curves and inhibitory concentrations (IC50-216 h) were obtained from the sigmoidal inhibition curves fitted by regression analysis. The effects of bacillamides on cell morphology and ultrastructure were also analysed by light and transmission electron microscopy. In general, the toxic cyanobacteria Microcystis aeruginosa, Aphanizomenon gracile, Anabaena circinalis and Anabaenopsis circularis were much more sensitive to bacillamides then the chlorophytes Ankistrodesmus falcatus and Scenedesmus obliquus. However, clear signs of morphological and ultrastructural changes induced by bacillamide were observed on both cyanobacteria and chlorophytes. Other cyanobacteria, namely the nostocalean Nodularia spumigena and the oscillatorialeans Leptolyngbya sp. and Planktothrix rubescens, exhibit higher tolerances to bacillamides, similar to that shown by different eukaryotic microalgae. Diatoms, on the other hand, proved to be quite as sensitive to most bacillamides as the most affected cyanobacteria. The properties of 5-iodo-Bacillamide (algicide or algistatic) were further investigated. This compound acted as an algistactic agent against eukaryotic algae and, depending on its concentration, acted as either an algicide or algistactic agent against most of the cyanobacteria tested. Although bacillamides cannot be considered as broad spectrum cyanobacterial algicides, different bacillamides might be of use in selectively controlling the growth of particular species of cyanobacteria.

The influence of light quality on akinete formation and germination in the toxic cyanobacterium Anabaena circinalis

Physiological control of akinete formation and subsequent germination is likely to be important in understanding and predicting how natural populations of cyanobacteria respond to their environment. While previous research has indicated nutrient limitation may be important in akinete formation new results presented here indicate that in the toxic and bloom-forming species Anabaena circinalis there was a profound effect of spectral quality. Under 40μmolphotonsm−2s−1 photosynthetically active irradiance (PAR) of predominately red irradiance akinete production was maximal at 2.1×10−4akinetesvegetativecell−1d−1, some 3000 times greater than the 6.5×10−8akinetesvegetativecell−1d−1 observed under equivalent PAR but predominately blue light. For cells grown under a range of predominantly red, white and green irradiance even short exposures to blue light reduced akinete formation rates by a factor of ten relative to controls, indicating that exposure to blue light inhibits akinete formation. Germination of akinetes was not influenced by the irradiance under which akinetes were formed: 88±4.1% (mean±1 S.D.) of akinetes germinated with no evidence of an effect on germination success due to their production under predominately red, white or green irradiance (germination of akinetes produced under blue light was not tested). Spectral quality had a significant impact on both vegetative cell and germling growth rates. The results indicate a significant reduction in the cellular differentiation of A. circinalis vegetative cells into akinetes that is mediated by blue light. In an ecological context the production of akinetes will be greater in environments with less blue light; potentially including those with slower flow, more stratification, less vertical mixing and more turbidity. The resulting spatial pattern of akinete production is likely to influence the location of akinetes in sediments and the development of subsequent blooms from excysting germlings.