Freshwater Blooms Research Articles

In vivo studies on the immunotoxic effects of microcystins on rabbit

Microcystins (MCs) are the toxic molecules produced by common cyanobacterium in freshwater blooms. Their toxicities raise severe health issues in livestock and human beings. In current study, the immunotoxic effects of MC-LR were investigated in rabbit through evaluating the dynamics of white blood cell (WBC) numbers and cytokine production such as interleukin-3 (IL-3), IL-4, IL-6, interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α). MCs at the high dose (50 μg MC-LReq kg(-1) ) significantly induced increase in the WBC number but decrease in the Th1 (IFN-γ, TNF-α) and Th2 (IL-3, IL-4, IL-6) production. In the low dose group(12.5 μg MC-LReq kg(-1) ), the number of WBC and the production of IFN-γ, IFN-α, IL-4, IL-3, and IL-6 increased gradually in first 12 h, reach the peaks at 12 h, and dropped after 24 h. Significantly positive correlations were found between the cytokines production of IL-4 and IL-6, IFN-γ and IFN-α, or IL-4 and IFN-γ. In conclusion, MC-LR is able to disturb the rabbit immune system and there exists time-dose response relationship in the MC-LR-eliciting perturbation, which probably give a better insight into investigating the immunotoxicity mechanisms of MCs in vivo. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2012.

A protein binding to an upstream sequence of ftsZ involved in coordination of DNA replication and cell division in Microcystis aeruginosa

The cyanobacterium Microcystis aeruginosa frequently forms blooms in eutrophic freshwater. Previously, we demonstrated that DNA replication and cell division are coordinated in M. aeruginosa NIES 298, and some part of this coordination is mediated by transcriptional regulation of the cell division gene ftsZ. In this study, to search for regulators involved in regulation of ftsZ transcription, we performed gel electrophoresis mobility shift assays (EMSA) using oligonucleotide probes corresponding to upstream sequences of ftsZ. Sequential EMSA analysis detected a protein binding to a 35-bp sequence (Fz35A) just upstream from the ftsZ start codon. Addition of excess unlabeled Fz35A caused disappearance of the retarded band, clearly indicating that this protein binds specifically to this sequence. While sequence comparison in cyanobacteria revealed conserved bases T-CC···T-CA among phylogenetically related species of Microcystis, mutation of these bases did not completely inhibit protein binding, suggesting that T-CC···T-CA contain at least one or more bases which are important to protein–DNA interaction. When EMSA was performed using crude protein extract from cells with DNA replication blocked, band shift was not observed. These data suggest that the protein factor may be involved in coordination of DNA replication and cell division via transcription control of ftsZ in M. aeruginosa.

The rise of harmful cyanobacteria blooms: The potential roles of eutrophication and climate change

Cyanobacteria are the most ancient phytoplankton on the planet and form harmful algal blooms in freshwater, estuarine, and marine ecosystems. Recent research suggests that eutrophication and climate change are two processes that may promote the proliferation and expansion of cyanobacterial harmful algal blooms. In this review, we specifically examine the relationships between eutrophication, climate change and representative cyanobacterial genera from freshwater ( Microcystis, Anabaena, Cylindrospermopsis), estuarine ( Nodularia, Aphanizomenon), and marine ecosystems ( Lyngbya, Synechococcus, Trichodesmium). Commonalities among cyanobacterial genera include being highly competitive for low concentrations of inorganic P (DIP) and the ability to acquire organic P compounds. Both diazotrophic (= nitrogen (N 2) fixers) and non-diazotrophic cyanobacteria display great flexibility in the N sources they exploit to form blooms. Hence, while some cyanobacterial blooms are associated with eutrophication, several form blooms when concentrations of inorganic N and P are low. Cyanobacteria dominate phytoplankton assemblages under higher temperatures due to both physiological (e.g. more rapid growth) and physical factors (e.g. enhanced stratification), with individual species showing different temperature optima. Significantly less is known regarding how increasing carbon dioxide (CO 2) concentrations will affect cyanobacteria, although some evidence suggests several genera of cyanobacteria are well-suited to bloom under low concentrations of CO 2. While the interactive effects of future eutrophication and climate change on harmful cyanobacterial blooms are complex, much of the current knowledge suggests these processes are likely to enhance the magnitude and frequency of these events.

Temperature and biotic factors influence bacterial communities associated with the cyanobacterium Microcystis sp.

Cyanobacterial blooms represent a nutritious niche for associated bacteria including potential pathogens for humans as well as livestock. We investigated bacterial community composition associated with Microcystis sp. using different approaches: batch experiments on Microcystis sp. or its enriched exudates, field enclosures (dialysis bags) and field sampling during natural blooms in freshwaters. Bacterial community composition associated with Microcystis sp. differed significantly with temperature, bacterial source community and number of incubated cyanobacterial strains. Interestingly, Actinobacteria of the AcI cluster were only present in the 20°C treatments and disappeared at higher incubation temperatures. Moreover, Archaea were present in all field samples but did not show any regional patterns, which is consistent with bacteria. Absence of Archaea in the experimental treatments indicates reduced growth under experimental conditions. In contrast, members of the genus Sphingomonas (Alphaproteobacteria), which includes species known as human pathogens, occurred in almost all samples. Thus Sphingomonadales seem to be an integral element of Microcystis sp. blooms - even affecting concentrations of microcystins as a result of their breakdown of the toxins. Depending on environmental conditions such as temperature, light, currents and nutrients, the role of heterotrophic Bacteria associated with Cyanobacteria can greatly vary by either increasing (pathogens) or decreasing (breakdown of toxins) health risks caused by mass developments of potentially toxic Cyanobacteria.

A peptidomic approach for monitoring and characterising peptide cyanotoxins produced in Italian lakes by matrix‐assisted laser desorption/ionisation and quadrupole time‐of‐flight mass spectrometry

In recent years, the occurrence of cyanobacterial blooms in eutrophic freshwaters has been described all over the world, including most European countries. Blooms of cyanobacteria may produce mixtures of toxic secondary metabolites, called cyanotoxins. Among these, the most studied are microcystins, a group of cyclic heptapeptides, because of their potent hepatotoxicity and activity as tumour promoters. Other peptide cyanotoxins have been described whose structure and toxicity have not been thoroughly studied. Herein we present a peptidomic approach aimed to characterise and quantify the peptide cyanotoxins produced in two Italian lakes, Averno and Albano. The procedure was based on matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry mass spectrometry (MALDI-TOF-MS) analysis for rapid detection and profiling of the peptide mixture complexity, combined with liquid chromatography/electrospray ionisation quadrupole time-of- flight tandem mass spectrometry (LC/ESI-Q-TOF-MS/MS) which provided unambiguous structural identification of the main compounds, as well as accurate quantitative analysis of microcystins. In the case of Lake Averno, a novel variant of microcystin-RR and two novel anabaenopeptin variants (Anabaenopeptins B(1) and Anabaenopeptin F(1)), presenting homoarginine in place of the commonly found arginine, were detected and characterised. In Lake Albano, the peculiar peptide patterns in different years were compared, as an example of the potentiality of the peptidomic approach for fast screening analysis, prior to fine structural analysis and determination of cyanotoxins, which included six novel aeruginosin variants. This approach allows for wide range monitoring of cyanobacteria blooms, and to collect data for evaluating possible health risks to consumers, through the panel of the compounds produced along different years.

A Cyanobacterial Toxin, Microcystin-LR, Induces Apoptosis of Sertoli Cells by Changing the Expression Levels of Apoptosis-Related Proteins

Toxic cyanobacterial blooms in freshwater have been considered as threats to human health. Microcystins are a family of cyclic polypeptides produced by cyanobacteria and are toxic to plants and animals. Microcystin-LR (MC-LR) is the most toxic variant among the microcystin family and could cause oxidative stress in various organs, including the reproduction system. The aim of this study was to investigate the effect of MC-LR on apoptosis of Sertoli cells that play an essential role in the development and maturation of sperm cells. Sertoli cells were isolated from healthy immature rats and cultured with MC-LR. The viability of Sertoli cells was decreased after treatment with MC-LR at 10 µg/ml for 24 h (P < 0.05). Moreover, the MC-LR-treated cells exhibited condensed chromatin and fragmented nuclei, features of apoptosis, as judged by Hoechst 33258 staining. We also analyzed the mRNA and protein levels of three apoptosis-related genes, p53, bax and bcl-2, using reverse transcription-polymerase chain reaction and Western blot analyses, respectively. Both p53 and bax function as promoters of apoptosis, while bcl-2 is an apoptotic suppressor. The mRNA and protein expression levels of p53 and bax were increased in Sertoli cells treated with MC-LR at 10 µg/ml compared with the control group (P < 0.05), while the bcl-2 protein levels were decreased in cells treated with MC-LR at 10 µg/ml (P < 0.05). Moreover, caspase-3 activity that is involved in the induction of apoptosis was significantly increased in Sertoli cells treated with MC-LR. These results indicate that MC-LR induces apoptosis of Sertoli cells.

Genotoxicity and potential carcinogenicity of cyanobacterial toxins – a review

The occurrence of cyanobacterial blooms has increased significantly in many regions of the world in the last century due to water eutrophication. These blooms are hazardous to humans, animals, and plants due to the production of cyanotoxins, which can be classified in five different groups: hepatotoxins, neurotoxins, cytotoxins, dermatotoxins, and irritant toxins (lipopolysaccharides). There is evidence that certain cyanobacterial toxins are genotoxic and carcinogenic; however, the mechanisms of their potential carcinogenicity are not well understood. The most frequently occurring and widespread cyanotoxins in brackish and freshwater blooms are the cyclic heptapeptides, i.e., microcystins (MCs), and the pentapeptides, i.e., nodularins (NODs). The main mechanism associated with potential carcinogenic activity of MCs and NOD is the inhibition of protein phosphatases, which leads to the hyperphosphorylation of cellular proteins, which is considered to be associated with their tumor-promoting activity. Apart from this, MCs and NOD induce increased formation of reactive oxygen species and, consequently, oxidative DNA damage. There is also evidence that MCs and NOD induce micronuclei, and NOD was shown to have aneugenic activity. Both cyanotoxins interfere with DNA damage repair pathways, which, along with DNA damage, is an important factor involved in the carcinogenicity of these agents. Furthermore, these toxins increase the expression of TNF-α and early-response genes, including proto-oncogenes, genes involved in the response to DNA damage, cell cycle arrest, and apoptosis. Rodent studies indicate that MCs and NOD are tumor promotors, whereas NOD is thought to have also tumor-initiating activity. Another cyanobacterial toxin, cylindrospermopsin (CYN), which has been neglected for a long time, is lately being increasingly found in the freshwater environment. The principal mechanism of its toxicity is the irreversible inhibition of protein synthesis. It is pro-genotoxic, and metabolic activation by cytochrome P-450 enzymes is needed for its genotoxic activity. In metabolically competent cells, it induces DNA strand breaks and exerts clastogenic and aneugenic activity. In addition, CYN increased the expression of p53 regulated genes involved in cell cycle arrest, DNA damage repair, and apoptosis. It also has cell transforming potential, and limited preliminary rodent studies indicate that CYN could have tumor-initiating activity. In 2010, the International Agency for Research on Cancer (IARC) classified MCLR as possible human carcinogen (Group 2B). Although there is not enough available information for the classification of other cyanobacterial toxins, the existing data from in vitro and in vivo studies indicate that NOD and especially CYN may be even more hazardous than MCLR to human and animal health. In addition in the environment, cyanobacterial toxins occur in complex mixtures as well as together with other anthropogenic contaminants, and numerous studies showed that the toxic/genotoxic potential of the extracts from cyanobacterial scums is higher than that of purified toxins. This means that the mixtures of toxins to which humans are exposed may pose higher health risks than estimated from the toxicological data of a single toxin. Future research efforts should focus on the elucidation of the carcinogenic potential of NOD, CYN, and the mixture of cyanobacterial extracts, as well as on the identification of possible novel toxins.

Isolation, identification and characterization of phytoplankton-lytic bacterium CH-22 against Microcystis aeruginosa

A bacterial strain named CH-22 showing phytoplankton-lytic activity against bloom-forming cyanobacterium Microcystis aeruginosa was isolated from Lake Chaohu of Anhui Province, China. The isolated strain was identified as Pseudomonas putida by morphology and homology research based on 16S rDNA. The phytoplankton-lytic activity was confirmed by reduction in cell number and chlorophyll a concentration of M. aeruginosa in an infected culture for a defined period. The initial bacterial and M. aeruginosa densities affected the phytoplankton-lytic activity significantly. When the 15% (150 μL/mL) concentration of bacterial cultures was infected, the highest phytoplankton-lytic activity reached to 98.8% after 7 days. When the initial M. aeruginosa density was less than 3×106 cells/mL, about 90.0% of chlorophyll a was removed. Obvious reduction in phycocyanin concentration in the treated M. aeruginosa suggests that isolated strain may possibly inhibit the synthesis of photosynthetic apparatus. Supernatants of bacterial cultures showed higher phytoplankton-lytic activity, suggesting that phytoplankton-lytic bacterium P. putida indirectly attacked M. aeruginosa cells by secretion of extracellular antialgal substances, which is characterized as anti-heat shock. The isolated P. putida also showed effective phytoplankton-lytic activity against a wide range of phytoplankton. These results suggest that indigenous bacteria isolated from eutrophic lake may be employed to regulate the ecological balance between the phytoplankton and bacteria, and consequently, to reduce the occurrence of cyanobacterial blooms in freshwaters.

Reassessing the ichthyotoxin profile of cultured Prymnesium parvum (golden algae) and comparing it to samples collected from recent freshwater bloom and fish kill events in North America

Within the last two decades, Prymnesium parvum (golden algae) has rapidly spread into inland waterways across the southern portion of North America and this organism has now appeared in more northerly distributed watersheds. In its wake, golden algae blooms have left an alarming trail of ecological devastation, namely massive fish kills, which are threatening the economic and recreational value of freshwater systems throughout the United States. To further understand the nature of this emerging crisis, our group investigated the chemical nature of the toxin(s) produced by P. parvum. We approached the problem using a two-pronged strategy that included analyzing both laboratory-grown golden algae and field-collected samples of P. parvum. Our results demonstrate that there is a striking difference in the toxin profiles for these two systems. An assemblage of potently ichthyotoxic fatty acids consisting primarily of stearidonic acid was identified in P. parvum cultures. While the concentration of the fatty acids alone was sufficient to account for the rapid-onset ichthyotoxic properties of cultured P. parvum, we also detected a second type of highly labile ichthyotoxic substance(s) in laboratory-grown golden algae that remains uncharacterized. In contrast, the amounts of stearidonic acid and its related congeners present in samples from recent bloom and fish kill sites fell well below the limits necessary to induce acute toxicity in fish. However, a highly labile ichthyotoxic substance, which is similar to the one found in laboratory-grown P. parvum cultures, was also detected. We propose that the uncharacterized labile metabolite produced by P. parvum is responsible for golden algae's devastating fish killing effects. Moreover, we have determined that the biologically-relevant ichthyotoxins produced by P. parvum are not the prymnesins as is widely believed. Our results suggest that further intensive efforts will be required to chemically define P. parvum's ichthyotoxins under natural bloom conditions.

Microcystin-producing blooms of Anabaenopsis arnoldi in a potable mountain lake in Saudi Arabia

This study reports for the first time the presence of Anabaenopsis arnoldi blooms in Saudi freshwaters. This species has been investigated with high cell densities (3.8 x 10(3)-264 x 10(3) cells mL(-1)) during June-November 2007 in Tendaha Lake, one of the major freshwater sources in Saudi Arabia. High temperature and conductivity, and a high concentration of phosphate, and low nitrate concentrations may have contributed to the formation of these blooms. The blooms were found to produce microcystins (MCYSTs) at concentrations up to 364 microg g(-1) dry weight as detected by an enzyme-linked immunosorbent assay. MCYSTs were also detected in the raw and treated water of the lake at concentrations (1.6-8.3 and 0.33-1.6 microg L(-1), respectively) exceeding the World Health Organization guideline level of 1 microg L(-1) for these toxins. HPLC analysis revealed that the extracts of A. arnoldi blooms contained MCYST-RR, -YR and two unidentified MCYSTs, but a pure culture of A. arnoldi isolated from Tendaha Lake during the present study produced MCYST-RR and -YR only. This is the first study to report MCYST production by A. arnoldi. Therefore, this cyanobacterium should be taken into consideration during monitoring of toxic cyanobacterial blooms in drinking and recreational water sources in the world, particularly arid and semi-arid countries including Saudi Arabia.

Removal of algal blooms in freshwater using magnetic polymer

Removal of algal blooms in freshwater using magnetic polymer was studied by magnetic field. Results showed that magnetic polymer at optimal loadings (4 mg/Lferroferric oxide modified with 1.6 mg/Lchitosan) could remove over 99% algal cells; meanwhile, the removal efficiency of COD, total nitrogen and phosphorus was found to be 85.0%, 73.9% and 28.7% respectively. Furthermore, effects of ionic strength, pH and cell concentration on the removal of algal cells were analyzed: ionic strength had a negative effect on the removal efficiency which increased with the increase of cell concentration and reached a maximum at pH 7.0.

Toxins produced in cyanobacterial water blooms - toxicity and risks

Cyanobacterial blooms in freshwaters represent a major ecological and human health problem worldwide. This paper briefly summarizes information on major cyanobacterial toxins (hepatotoxins, neurotoxins etc.) with special attention to microcystins-cyclic heptapeptides with high acute and chronic toxicities. Besides discussion of human health risks, microcystin ecotoxicology and consequent ecological risks are also highlighted. Although significant research attention has been paid to microcystins, cyanobacteria produce a wide range of currently unknown toxins, which will require research attention. Further research should also address possible additive, synergistic or antagonistic effects among different classes of cyanobacterial metabolites, as well as interactions with other toxic stressors such as metals or persistent organic pollutants.

Algicidal effect of Pseudomonas fluorescens against Stephanodiscus Hantzschii (Bacillariophyceae) during winter freshwater blooms: Biological impact of algicidal activity in mesocosms

Algicidal effect of Pseudomonas fluorescens against Stephanodiscus Hantzschii (Bacillariophyceae) during winter freshwater blooms: Biological impact of algicidal activity in mesocosms

Metagenomic analysis of a freshwater toxic cyanobacteria bloom

High molecular weight (HMW) DNA prepared from a toxic freshwater cyanobacterial bloom sample was used to construct a PCR-generated 75-clone, 16S rRNA gene library and a 2850-clone bacterial artificial chromosome (BAC) library. Phylogenetic analysis of the 16S rRNA gene library demonstrated that members of eight phyla of domain Bacteria, which included Cyanobacteria, Actinobacteria, Verrucomicrobium, Bacteriodetes, Planctomycetes, Chloroflexi, Candidate Division OP10 and Alpha-, Beta- and Gammaproteobacteria, were present in the bloom community. Diversity estimates determined from 16S rRNA gene analysis and direct cell counts and morphological identification of phytoplanktons suggested that the bloom community was dominated by members of the genera Aphanizomenon and Cylindrospermopsis, phylum Cyanobacteria. BAC-end sequencing of 37 randomly selected clones and subsequent sequence analysis provided a snapshot of the total bloom community putative metabolic activities. The sequencing of the entire inserts of seven clones (clones designated 578, 67, 142, 543, 905, 1664 and 2089) selected from BAC-end sequence studies resulted in the generation of a total of 144-kb sequence data and in the identification of 130 genes for putative proteins representing at least four phyla, Proteobacteria, Actinobacteria, Bacteroidetes and Cyanobacteria. This is the first report on a snapshot analysis of a limited metagenome of a toxic cyanobacterial freshwater bloom.

Effects of Biological Control Agents on Nuisance Cyanobacterial and Diatom Blooms in Freshwater Systems

Biological control agents such as bacteria and ciliates were tested alone and in combination for their abilities to decrease densities of the warm-weather cyanobacterium, Microcystis aeruginosa, and the cold-weather centric diatom, Stephanodiscus hantzschii. The growth of Microcystis aeruginosa was effectively suppressed by the algicidal bacterium, Streptomyces neyagawensis, and the predator heterotrich ciliate, Stentor roeselii. However, co-treatment increased the algal density rather than decreasing it, suggesting that Streptomyces neyagawensis and Stentor roeselii have an antagonistic relationship. Additional experiments revealed that the density of Stephanodiscus hantzschii was effectively reduced by the bacterium, Pseudomonas putida, and by the abovementioned strain of Stentor roeselii. Co-treatment had a greater antialgal effect than treatment with either bio-agent alone, indicating that the two act synergistically. These results suggest the potential antialgal efficacy of treatments with multiple biological control agents, providing new insight that may be useful for the bioremediation of nuisance algal blooms in freshwater.

MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF PLANKTONIC CYANOBACTERIA FROM BELGIUM AND LUXEMBOURG1

For the first time in Belgium and Luxembourg, the diversity and taxonomy of 95 cyanobacterial strains isolated from freshwater blooms were assessed by the comparison of phenotypes and partial 16S rRNA gene sequences. The results showed the high diversity of nanoplanktonic, picoplanktonic, and benthic–periphytic cyanobacteria accompanying the main bloom‐forming taxa. Indeed, besides 15 morphotypes of bloom‐forming taxa, seven non‐bloom‐forming planktonic morphotypes and 11 morphotypes from benthic–periphytic taxa were isolated in culture from the plankton samples of 35 water bodies. The bloom‐forming strains belonged to the genera Microcystis, Woronichinia, Planktothrix, Anabaena, and Aphanizomenon, whereas the other strains isolated from the same samples were assigned to the nanoplanktonic Aphanocapsa, Aphanothece, Snowella, and Pseudanabaena; to the picoplanktonic Cyanobium; and to the benthic–periphytic Geitlerinema, Komvophoron, Leptolyngbya, Lyngbya, Phormidium, Calothrix, Nostoc, and Trichormus. The results supported both the polyphyletism of genera such as Aphanocapsa, Aphanothece, Leptolyngbya, Geitlerinema, Anabaena, and Aphanizomenon as well as the validity of genera such as Microcystis, Planktothrix, and Pseudanabaena with gas vesicles and cells constricted at the cross wall. The results obtained showed the close relationship between Snowella and Woronichinia for which very few sequences exist. The first sequence of Komvophoron appeared poorly related to other available cyanobacterial sequences. Although in a few cases a good agreement existed between phenotypic and genotypic features, there was generally a discrepancy. Strains with identical morphotypes show small differences in the 16S rRNA sequences, which might be related to the different chemical properties of their habitats. The results showed the importance of the polyphasic approach in order to improve the taxonomy of cyanobacteria.

HAB outreach using multimedia: integrating ocean research and education

This paper highlights a few of the education and outreach products on harmful algal blooms (HABs) that have been developed at Bigelow Laboratory for Ocean Sciences, a non-profit organisation dedicated to marine biological research and education. The 'Toxic & Harmful Algal Blooms' web page (www.bigelow.org/hab) provides information about blooms, where they occur in US waters, foodweb effects, how toxins affect humans, and causative species. The 'Special topics' section features freshwater blooms, ocean colour, detection methods and research on South African HABs. This online resource is augmented by educational activities (www.bigelow.org/edhab) that allow teachers to use the topic of HABs as a vehicle to investigate the role that algae play in our environment. The multimedia CD-ROM, 'Phytopia: Discovery of the Marine Ecosystem', is a data-rich resource with tutorials, interactive tools, high-quality graphics and movie clips designed for users of various skill and interest levels. 'Phytopia' enables those without appropriate equipment or data to investigate the microscopic marine ecosystem. Since its release in May 2003, over 6 100 copies have been requested from users in 61 countries for formal and informal education and research.

The effect of environmental parameters and cyanobacterial blooms on phytoplankton dynamics of a Portuguese temperate Lake

The increasing occurrence of cyanobacterial blooms in freshwaters is of great concern due to the ability of many cyanobacteria to produce cyanotoxins. In the present work, the eutrophied Vela Lake (Central Portugal), used for recreational purposes and as a water source for agriculture, was monitored every fortnight between 2000 and 2001. Phytoplankton diversity and densities were measured and correlated to environmental parameters. A seasonal phytoplanktonic succession was observed and it was mainly correlated with conductivity, temperature, total suspended solids and nutrients availability (particularly phosphorus). Diatoms were dominant during winter months (inferior temperatures and higher nutrients availability) followed by green algae in early spring and then cyanobacteria from late spring until early autumn (less nutrient availability and higher temperatures). A massive cyanobacterial bloom of Aphanizomenon flos-aquae occurred early in May 2001 and was preceded by the lowest nitrogen levels measured in the water during all the study period. At the time of this bloom senescence, dissolved oxygen was severely depleted and a massive death of ichthyofauna was recorded. A Microcystis aeruginosa bloom was also detected in July 2001 and it occurred following a rapid decrease in abundance of green algae and diatoms. By considering not only the environmental parameters but also the occurrence of cyanobacterial blooms as explanatory variables in a canonical correspondence analysis, the variance explained for the phytoplanktonic assemblage during the study period was increased in about 7% achieving a total of 61.0%, indicating a correlation that may be due to the known competitive advantage and/or allelopathy of the bloom-forming cyanobacteria towards microalgae.

Lysis of Aphanizomenon flos-aquae (Cyanobacterium) by a bacterium Bacillus cereus

A phytoplankton-lytic (PL) bacterium, Bacillus cereus, capable of lysing the bloom-forming cyanobacterium. Aphanizomenon flos-aquae was isolated from Lake Dianchi of Yunnan province, China. This bacterium showed lytic activities against a wide range of cyanobacteria/algae, including A. flos-aquae, Microcystis viridis, Microcystis wesenbergi, Microcystis aeruginosa, Chlorella ellipsoidea, Oscillatoria tenuis, Nostoc punctiforme, Anabaena flos-aquae, Spirulina maxima, and Selenastrum capricornutum. Chlorophyll a contents, phycocyanin contents, and photosynthetic activities of the A. flos-aquae decreased evidently in an infected culture for a period. Bacterium B. cereus attacked rapidly A. flos-aquae cells by cell-to-cell contact mechanism. It was shown that the lysis of A. flos-aquae began with the breach of the cyanobacterial cell wall, and the cyanobacterial cell appeared abnormal in the presence of the PL bacterium. Moreover, transmission electron microscope examinations revealed that a close contact between the bacterium and the cyanobacterium was necessary for lysis. Some slime extrusions produced from B. cereus assisted the bacterial cells to be in close association with and lyse the cyanobacterial cells. These findings suggested that this bacterium could play an important role in controlling the Aphanizomenon blooms in freshwaters. (c) 2006 Elsevier Inc. All rights reserved.

Eutrophication in Australian Rivers, Reservoirs and Estuaries – A Southern Hemisphere Perspective on the Science and its Implications

Australian science has made rapid advances in the last decade in understanding eutrophication processes in inland waters and estuaries. The freshwater research on which these advances are based was triggered by well-publicised blooms of cyanobacteria during the 1980s and early 1990s, particularly a 1000 km long bloom on the Darling River. In estuaries the study which greatly enhanced our understanding but simultaneously served to stimulate further research into estuarine eutrophication, the Port Phillip Bay Study, was initially designed to address perceived problems of toxicants in the Bay but provided profound insights into drivers for, and ecosystem responses to, eutrophication. Subsequent estuarine research has largely been stimulated by management questions arising from Australia’s increasing coastal development for residential purposes. The research has shown that some of the beliefs extant at the time of the blooms were incorrect. For example, it is now clear that stratification and light penetration, not nutrient availability, are the triggers for blooms in the impounded rivers of southeastern Australia, although nutrient exhaustion limits the biomass of blooms. Again, nitrogen seems to play as important a role as phosphorus does in controlling the biomass of these freshwater blooms. The research has also shown that aspects of eutrophication, such as nutrient transport, are dominated by different processes in different parts of Australia. Many of the biophysical processes involved in eutrophication have now been quantified sufficiently for models to be developed of such processes as sediment-nutrient release, stratification, turbidity and algal growth in both freshwater and estuarine systems. In some cases the models are reliable enough for the knowledge gained in particular waterbodies to be applied elsewhere. Thus, there is now a firm scientific foundation for managers to rely upon when managing algal blooms. Whilst these findings have already been presented to managers and communities throughout Australia, there is still a considerable way to go before they are absorbed into their modus operandi.