Distribution and toxicity of a new colonial Microcystis aeruginosa bloom in the San Francisco Bay Estuary,California

The first distribution, biomass and toxicity study of a newly established bloom of the colonial cyanobacteria Microcystis aeruginosa was conducted on October 15, 2003 in the upper San Francisco Bay Estuary. Microcystis aeruginosa was widely distributed throughout 180 km of waterways in the upper San Francisco Bay Estuary from freshwater to brackish water environments and contained hepatotoxic microcystins at all stations. Other cyanobacteria toxins were absent or only present in trace amounts. The composition of the microcystins among stations was similar and dominated by demethyl microcystin-LR followed by microcystin-LR. In situ toxicity computed for the >75 m cell diameter size fraction was well below the 1 g l^–1 advisory level set by the World Health Organization for water quality, but the toxicity of the full population is unknown. The toxicity may have been greater earlier in the year when biomass was visibly higher. Toxicity was highest at low water temperature, water transparency and salinity. Microcystins from the bloom entered the food web and were present in both total zooplankton and clam tissue. Initial laboratory feeding tests suggested the cyanobacteria was not consumed by the adult copepod Eurytemora affinis, an important fishery food source in the estuary.     

Antialgal activity of a hepatotoxin-producing cyanobacterium,Microcystis aeruginosa

Antimicrobial activity of toxin produced by a freshwater bloom-forming cyanobacterium Microcystis aeruginosa has been studied. When tested against certain green algae, cyanobacteria, heterotrophic bacteria and fungi, the toxin inhibited growth of only green algae and cyanobacteria. The toxin has been partially purified employing Thin layer chromatography (TLC) and High-performance liquid chromatography (HPLC) techniques and appears to be microcystin-LR (leucine–arginine). Both crude and purified toxins showed toxicity to mice, the clinical symptoms in test mice being similar to those produced by hepatotoxin. Purified toxin at a concentration of 50 g ml^–1 caused complete inhibition of growth followed by cell lysis in Nostoc muscorum and Anabaena BT1 after 6 days of toxin addition. Addition of toxin (25 g ml^–1) to the culture suspensions of the Nostoc and Anabaena strains caused instant and drastic loss of O₂ evolution. Furthermore a marked reduction (about 87%) in the ¹⁴CO₂ uptake was also observed at a concentration of 50 g ml^–1. Besides its inhibitory effects on photosynthetic processes, M. aeruginosa toxin (50 g ml^–1) also caused 90% loss of nitrogenase activity after 8 h of its addition. Experiments performed with ¹⁴C-labelled toxin indicate that the toxin uptake by cyanobacterial cells occurs both in light and dark. These results demonstrate that the toxin is strongly algicidal and point to the possibility that it may have an important role in establishment and maintenance of toxic blooms of M. aeruginosa in freshwater ecosystems. The relative significance of the hepatotoxic effect and the algicidal effect of the toxin is discussed with reference both to survival and dominance of M. aeruginosa in nature.     

Seasonal variations of Microcystis populations in sediments of Lake Biwa, Japan

Seasonal variations of colony numbers of Microcystis aeruginosa(Kütz.) Kütz. and M. wesenbergii(Komárek) Komárek in N. V. Kondrat. in sediments of Lake Biwa were investigated over a period of 1 year. At two stations located in the shallow South Basin of Lake Biwa (ca. 4 m water depth), the colony number of Microcystisfluctuated seasonally. The number had a tendency to gradually decrease from winter to early summer, while it increased through mid-summer and autumn. Since the Microcystispopulation in sediment was rather small, intensive growth and accumulation in the water column should be important for the formation of Microcystisblooms in Lake Biwa. Microcystiscolonies in the sediment samples after June were observed to be floating in a counting chamber under a microscope. The observation suggests that the recruitment of Microcystis colonies into the water column mostly occurs in early summer. The number of Microcystiscolonies in the deep North Basin of Lake Biwa (70 – 90 m water depth) was larger than in the South Basin. Because the seasonal variation of colony numbers was not observed in the North Basin, and Microcystiscells do not have gas vesicles, these colonies will not return into the water column. The colonies isolated from the sediment of the North Basin were able to grow in cultured conditions, in the same way as those from the sediment of the South Basin. Therefore, Microcystiscolonies may survive for a long time under stable conditions of low temperature (ca. 8 °C) and darkness, in the sediment of the deep North Basin, accumulating gradually each year.     

Combined influences of particulate and dissolved factors in the toxicity of Microcystis aeruginosa (NRC-SS-17) to the rotifer Brachionus calyciflorus

The rotifer Brachionus calyciflorus is subject to the combined influence of particulate and dissolved factors derived from the toxic cyanobacterium Microcystis aeruginosa. Toxicity manifests itself through reduction of cohort survivorship and probably though reduction of cohort reproduction. Toxic effects are seen only when there is a particulate food material available in suspension, either M. aeruginosa itself or another food type which may act as a carrier for a dissolved toxic factor. Regardless of exact mechanism, the presence of a toxic strain of this blue-green may lead to diminution of population growth of co-occurring rotifer populations.     

Spatial distribution of seston in an artificially mixed system

Seston size distribution was determined with a Coulter Counter to investigate seston interaction and its effects on phytoplankton production. Spatial distribution patterns of the non-productive component of the seston were as complex as those commonly associated with algae. Seston might interact influencing production by changes in optical depth, abrasive actions and nutrient adsorption.     

Synthesis of glucosylglycerol in salt-stressed cells of the cyanobacterium Microcystis firma

The unicellular cyanobacterium Microcystis furma tolerates salinity by accumulating the osmoprotective compound glucosylglycerol. After salt shock, the initial rate of glucosylglycerol synthesis is independent of the NaCl concentration used. In pulse chase experiments with NaH¹⁴CO₃, synthesis of glucosylglycerol by salt-adapted cells was found to be rapid, whereas no sign of its breakdown was detected. Therefore, it is concluded that no turnover of glucosylglycerol takes place in salt-adapted cells. The specific capacity of the glucosylglycerol-forming enzyme system may be one reason for the salt resistance limit.Abbreviation GG glucosylglycerolDedicated to Prof. Dr. Eike Libbert on the occasion of his 60th birthday     

Genetic diversity of Microcystis populations in a bloom and its relationship to the environmental factors in Qinhuai River, China

Cyanobacterial blooms, forming massive scum and various cyanotoxins, increasingly spread in a wide range of freshwater ecosystems. One heavy Microcystis bloom occurred in the entire Qinhuai River basin in 2010 summer for the first time. To determine the Microcystis populations and their spatial distributions along Qinhuai River, a molecular approach was applied by sequencing the DNA library based on the internal transcribed spacer sequences of 16-23S rRNA (ITS). The parsimony network (TCS) analysis showed that 9 groups were formed based on the main 24 genotypes, and each group was dominated by one highly represented root sequence. Marked changes in the composition and proportion of the Microcystis ITS genotype were detected from the upper to the lower reaches. The seed sources forming the bloom were probably located at 4 different locations. Furthermore, it was found that pH was the primary factor affecting the spatial distribution of the main genotype group among samples.     

Computer simulation modelling of buoyancy change in Microcystis

This paper reviews the development of the SCUM seriesof models and presents additional algorithms forcalculating surface radiation flux and growth. Thefirst SCUM models used data obtained by laboratoryinvestigation of Oscillatoria agardhii byKromkamp & Walsby (1990). However when applied toother species the models became unstable. More recentattempts have taken a different and more theoreticalapproach combining lake mixing and modellingcomponents of SCUM with a buoyancy routine (CYANARA)developed at the Institute of Freshwater Ecology.Model algorithms and sample model results are brieflydescribed. The growing importance of the World Wide Webin modelling is highlighted and explained.     

Toxicity and biodegradation of fluometuron by selected cyanobacterial species

The Biodegradation capabilities of six selected cyanobacterial species for fluometuron, a phenylurea herbicide, as well as its inhibitory effect on chlorophyll a content were investigated. The selected species (three strains of Microcystis aeruginosa, Anabaena cylindrica, A. flos-aquae and A. spiroides) were subjected to three elevated concentrations of fluometuron (0.14, 0.7 and 1.4 mg/ml) for different exposure times (1–5 days). Results revealed that biodegradation of fluometuron is species-dependent and positively correlated with the exposure time, reaching maximum efficiency after 5 days at all the investigated concentrations. All the species tested showed generally great ability to degrade the compound even at the highest concentration with specific variations among them. Biodegradation efficiencies of fluometuron by the selected species were in the following ranges; 39.2–99.9; 87.5–100; and 93.2–100 at 0.14; 0.7 and 1.4 mg fluometuron/ml respectively. It was noticed that the gradual increase in the pesticide concentration enhances its biodegradability by the selected algal species. Variations according to species as well as exposure time were discussed. The highest fluometuron concentration (1.4 mg/l) showed the highest inhibition of chlorophyll a content in the tested species and toxicity was also species- and time-dependent.     

Evaluation of Microcystis as food for zooplankton in a eutrophic lake

Four experiments were conducted to evaluate Microcystis as food for zooplankton in Lake Kasumigaura, and the following results were obtained. (1) Moina micrura (Cladocera) showed little growth and no reproduction when the animal was reared with Microcystis cultured in the laboratory. The animal did not grow nor reproduce well when Chlorella was mixed with Microcystis as food. (2) Moina micrura assimilated Microcystis much less than Chlorella when the animal fed on single species of Microcystis or a mixture with Chlorella. (3) Microcystis collected from Lake Kasumigaura could not be utilized by Moina micrura even though the colonies were broken up into edible sizes. However, the alga turned into utilizable food when it was decomposed. (4) No inhibitors of Moina micrura population growth could be found in the non-filtered water of Lake Kasumigaura where Microcystis was blooming heavily. Decomposed Microcystis seemed to be utilized by zooplankton as an important food source in Lake Kasumigaura.     

Diurnal changes in leaf gas exchange and chlorophyll fluorescence in tropical tree species with contrasting light requirements

Interspecific ecophysiological differences in response to different light environments are important to consider in regeneration behavior and forest dynamics. The diurnal changes in leaf gas exchange and chlorophyll fluorescence of two dipterocarps, Shorea leprosula (a high light-requiring) and Neobalanocarpus heimii (a low light-requiring), and a pioneer tree species (Macaranga gigantea) growing in open and gap sites were examined. In the open site, the maximum net photosynthetic rate (P_n), photosystem II (PSII) quantum yield (; F/Fm), and relative electron transport rate (r-ETR) through PSII at a given photosynthetic photon flux density (PPFD) was higher in S. leprosula and M. gigantea than in N. heimii, while non-photochemical quenching (NPQ) at a given PPFD was higher in N. heimii. The maximum values of net photosynthetic rate (P_n) in M. gigantea and S. leprosula was higher in the open site (8–11 mol m^–2 s^–1) than in the gap site (5 mol m^–2 s^–1), whereas that in N. heimii was lower in the open site (2 mol m^–2 s^–1) than in the gap site (4 mol m^–2 s^–1), indicating that N. heimii was less favorable to the open site. These data provide evidence to support the hypothesis that ecophysiological characteristics link with plants regeneration behavior and successional status. Although P_n and stomatal conductance decreased at midday in M. gigantea and S. leprosula in the open site, both r-ETR and leaf temperature remained unchanged. This indicates that stomatal closure rather than reduced photochemical capacity limited P_n in the daytime. Conversely, there was reduced r-ETR under high PPFD conditions in N. heimii in the open site, indicating reduced photochemical capacity. In the gap site, P_n increased in all leaves in the morning before exposure to direct sunlight, suggesting a relatively high use of diffuse light in the morning.     

Effects of the mixotrophic flagellate Ochromonas sp. on colony formation in Microcystis aeruginosa

The aim of this study was to investigate the interactions between the cyanobacteria (Microcystis aeruginosa) and the potential grazer (Ochromonas sp.) with regard to colony formation. Two kinds of treatments were carried out: (i) In the dialyse experiment Microcystis aeruginosa and Ochromonas sp. were physically separated by a dialyse tubing. (ii) In the contact experiment interactions between Microcystis aeruginosa, heterotrophic bacteria and Ochromonas sp. in different concentrations were investigated. In one treatment where the predator Ochromonas sp. came in direct contact with Microcystis, aggregates were formed.In the contact experiment, there were some interactions between the predator Ochromonas sp. and the two groups of prey, Microcystis aeruginosa and heterotrophic bacteria. When exposed to a low initial Ochromonas sp. concentration, Microcystis aeruginosa decreased and then remained stable in concentration. Ochromonas sp. switched to feed on heterotrophic bacteria and increased. At a high initial Ochromonas sp. concentration Microcystis was grazed down.     

Heptapeptide toxin production during the batch culture of two Microcystis species (Cyanobacteria)

Changes in the content of cyclic heptapeptide hepatotoxins called microcystins were investigated during batch culture of two Microcystis species using high performance liquid chromatography. After adsorption to ODS-silica gel cartridges and elution with methanol, the toxins were analyzed and quantified by HPLC. 35 μg per 100 mg dry cells of microcystin-RR, 34 μg of -YR and 43 μg of -LR were present at the beginning of the exponential growth phase of M. viridis. Microcystin-RR increased markedly towards the end of the exponential phase with the maximum content of 112 μg per 100 mg cells was measured at the late stage of the exponential phase. A remarkable increase of microcystin-YR from 130 μg per 100 mg cells to 1020 μg was observed during the exponential phase of a highly toxic strain of M. aeruginosa. However no clear differences were found in the pattern of change among the three toxins during the growth course.     

Isolation and purification of Australian isolates of the toxic cyanobacteriumMicrocystis aeruginosa Kütz

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

Elemental composition of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> under conditions of lake nutrient depletion

Electron probe X-ray microanalysis (XRMA) was used to determine the elemental composition of the blue-green alga, Microcystis aeruginosa, in a stratified freshwater lake during the late summer. Colonies of this alga were initially observed in mid-July, at a time when phosphorus concentration in the lake water had decreased to minimal levels (total P 0.04 mg l⁻¹). The P quota of these cells was high (mean concentration 132 mmol kg⁻¹ dry weight) with a cell P to lake water P concentration ratio of 10⁵. The elemental concentrations of Microcystis remained relatively stable throughout the sampling period (July–September), with mean cell concentrations of Mg, P, S and Ca showing no significant changes. Mean elemental ratios and the ratio of monovalent/divalent cations were also relatively constant (SE <10% mean). The pattern of cell elemental associations, determined by Factor and Pearson correlation analysis, was consistent throughout – with Mg, P, K and S forming a core tetrad of inter-correlated elements. The relative constancy of cell composition seen in Microcystis would be expected of an alga with a K-selection strategy. The continued high P quota over a period of nutrient depletion in lake water is consistent with the ability of this alga to sink to nutrient-rich lower regions of the water column.     

Risk evaluation of cyanobacteria-dominated algal blooms in a North Louisiana reservoir

Cyanobacteria blooms may produce toxins thatare harmful to invertebrates and fishinhabiting aquatic systems. The objectives ofthis risk evaluation were: (1) to investigatethe potential toxicity (i.e., adverse effectsof cyanobacteria on the survival, reproduction,and behavior) of Lyngbya-dominated algalblooms from a North Louisiana reservoir to Daphnia magna and Pimephales promelas;and (2) to develop mitigation strategies forthis cyanobacteria infestation using physicaland chemical methods. Survival and reproductionof D. magna populations significantlydecreased after exposure to reservoircyanobacteria collected in spring in comparisonwith populations of test organisms exposed toeither Chlorophyta species or a combination ofreservoir cyanobacteria and Chlorophytaspecies. In April 1998, reservoir cyanobacteriaalso elicited a significant avoidance reactionby juvenile P. promelas (20–30 d).However, cyanobacteria collected in August andDecember (1997) did not cause adverse effectsfor either D. magna or P. promelasin terms of survival, reproduction, orbehavior. A physical control method, loweringthe water level of the reservoir (i.e.,drawdown), was simulated in the laboratory for8, 20, and 35 d. After re-saturation of algalpopulations with nutrient enriched medium, theyrecovered to 132.9, 129.4, and 23.7% oforiginal chlorophyll a concentrations,respectively. Herbicide application resulted in>78% decrease in chlorophyll aconcentration of reservoir cyanobacteria by7-d after initial herbicide application. Todecrease risk(s) of Lyngbya-dominatedcyanobacteria and maintain seasonal control inthis reservoir, drawdown in conjunction withherbicide application or recurrent herbicideapplication is recommended prior to onset ofcyanobacteria proliferation.     

Distribution of benthic macroinvertebrates in an artificially destratified reservoir

A total of 76 taxa of benthic macroinvertebrates as collected from Ham's Lake, Oklahoma, during 1974 and 1975. The composition and density of the benthic assemblage was similar to that of other Oklahoma reservoirs. The number of species and density of macroinvertebrates decreased from March to the end of July, 1975 Species diversity and biomass did not change significantly with time. Number of species and species diversity decreased with depth on all sampling periods. The most pronounced changes occurred between 4 and 5 m during periods of thermal stratification and hypolimnion anoxia. Artificial destratification removed the thermocline from Ham's Lake within 2 wk. More gradually, the deep waters were reoxygenated. Destratification did not substantially alter the depth distribution of benthic macroinvertebrates until oxygen level of the deep water was increased. Research supported with funds from the Oklahoma Water Resources Research Institute and the Bureau of Reclamation.     

Diurnal and spatial patterns of Phytoseiidae in the citrus canopy

Phytoseiid mites were sampled in a grapefruit orchard at various times of the day to study their diurnal and seasonal distributions in the tree canopy. Samples were collected on 14, 20 and 28 October 1999 at 2 h intervals from 0600 to 2200 h. Similar samples were collected in a grapefruit orchard at 3 h intervals from 0600 to 2100 h on 9 and 16 March and on 17 and 24 August 2000 for phytoseiid mites. No differences in numbers of phytoseiid motiles were observed among the hours sampled in any of the three months. However, significant differences were observed in the number of phytoseiids per leaf based on location within the tree (eastern, western sides of the canopy or interior). Interior leaves collected in March and August 2000 had higher numbers of phytoseiids than exterior leaves taken from either the eastern or western sides of the tree canopy. Phytoseiids were more abundant in the March 2000 samples (mean = 1.10 phytoseiids/leaf) than in either October 1999 or August 2000 samples (mean = 0.16 and 0.19 phytoseiids/leaf, respectively). Prevalent phytoseiid species were Typhlodromalus peregrinus (Muma) (42.1%) and Iphiseiodes quadripilis (Banks) (50.4%) in October 1999, Typhlodromalus peregrinus (Muma) (76.2%) in March 2000, and Euseius mesembrinus (Dean) (54%) in August 2000.     

Diurnal and seasonal variations of nitrogen fixation and photosynthesis in cyanobacterial mats

In situ measurements of nitrogenase activity and photosynthesis were performed simultaneously in cyanobacterial mats of intertidal sand flats of the Southern North Sea. Two types of cyanobacterial mats, which differed in species composition and biomass content, were investigated. The measurements were done monthly during 3 years to detect seasonal variations of nitrogen fixation and photosynthesis. Diurnal variations were investigated as well. The results showed that (i) freshly colonized sediment with the cyanobacteriumOscillatoria limosa as the dominant organism revealed the highest specific nitrogenase activities (ii) nitrogenase activities were highest in spring and summer, when mat development was initiated and (iii) diurnal fluctuations of nitrogenase activity indicated that it occurred temporally separated from oxygenic photosynthesis.     

Diurnal changes in the fine structure of photoreceptors in an abalone,Nordotis discus

Summary The ultrastructure of the synapses in the brain of the monogenean Gastrocotyle trachuri (Platyhelminthes) is described. The synapses consist of one presynaptic terminal separated by a uniformly wide synaptic cleft, from one or more postsynaptic elements. The presynaptic terminals are characterized by the presence of paramembranous dense projections and associated synaptic vesicles. The postsynaptic elements while possessing membrane densities, are usually devoid of vesicles.The structure of the synapses in the brain of Gastrocotyle is compared to synapses from other platyhelminths.