Changes in extracellular polysaccharide content and morphology of Microcystis aeruginosa at different specific growth rates

The cyanobacterium Microcystis mainly exists in colonies under natural conditions but as single cells in typical laboratory cultures. Understanding the mechanism by which single cells form small and large colonies can provide a deeper insight into the life history of Microcystis and the mechanisms of Microcystis bloom formation. In this paper, Microcystis aeruginosa cultured under varying light intensities and temperatures exhibited different specific growth rates. Correlations were found between the specific growth rate, extracellular polysaccharide (EPS) content, and morphology of M. aeruginosa. Under low light intensities and temperatures, M. aeruginosa formed small colonies (maximum colony size approximately 100 μm) and exhibited low specific growth rates. By contrast, standard culture conditions yielded single or paired cells with high specific growth rates. Moreover, the EPS content decreased dramatically with increasing specific growth rate. A significant positive linear relationship was observed between the EPS content per cell and colony size. High EPS content and colony formation were associated with low specific growth rates. The specific growth rate in laboratory cultures was higher than the in situ growth rate under natural conditions. This result may explain why Microcystis normally exists as single cells or (more rarely) as paired cells in axenic laboratory cultures after long-term cultivation, but forms colonies under natural conditions.     

The Influence of Toxic and Filamentous Blue-green Algae on Feeding and Population Growth of the Rotifer Brachionus rubens

The effect of toxic and of filamentous blue-green algae on feeding and population growth of the rotifer Brachionus rubens was investigated in laboratory experiments. A toxic strain of Microcystis aeruginosa was ingested, but rotifers cultured with Microcystis died faster than nonfed controls. The rigid filaments of Cylindrospermopsis raciborskii were not ingested, reduced the ingestion of simultaneously offered algae, and depressed population growth rates. The soft filaments of Anabaena flos-aquae were ingested at a moderate rate, did not reduce ingestion of other algae, and were used as an additional food in population growth experiments.     

Effects of toxic and non-toxic cyanobacteria on the life history of tropical and temperate cladocerans

1. This study compares the effects of four toxic strains of Microcystis aeruginosa on tropical and temperate Cladocera. Survival was tested in acute toxicity experiments using Microcystis alone or in mixtures with the edible green algae Ankistrodesmus falcatus. The effect of chronic exposure on population growth was estimated in life‐table experiments by varying the proportion of Microcystis and the green alga. Nutritional deficiency was assessed using a non‐toxic cyanobacterium in a zooplankton growth experiment. Feeding inhibition was tested using a C‐labelled green alga as a tracer in mixtures with toxic Microcystis.
2. Toxicity varied consistently between Microcystis strains, while sensitivity varied consistently between cladoceran species. However, no relationship was found between sensitivity and geographical origin or cladoceran body size. Two small‐bodied cladocerans from the same tropical lake, Ceriodaphnia cornuta and Moinodaphnia macleayi, were the least sensitive and most sensitive species, respectively.
3. Surprisingly, two small tropical cladocerans survived longer without food than did three large Daphnia species and a third small tropical species.
4. Each of the three tropical Microcystis strains strongly reduced the population growth rate (little ‘r’) and reproductive output of each cladoceran, this reduction being proportional to the percentage of toxic cells in the diet.
5. As the sole food source, the non‐toxic cyanobacterium, Synechococcus elongatus, supported poor growth in M. macleayi. The nutritional deficiency was overcome when Synechococcus was mixed with either Ankistrodesmus or an emulsion rich in omega‐3 fatty acids.
6. Microcystis inhibited the feeding rate of two cladocerans, even when it comprised only 5% of a mixture with the green algae A. falcatus.
7. Differences in sensitivity to the toxic cyanobacterium appear to be associated with differences in life history between the cladoceran species rather than differences between tropical and temperate taxa. Slow‐growing species that are resistant to starvation appear less sensitive to toxic Microcystis than fast‐growing species, which also tend to die more quickly in the absence of food.     

Morphological and physiological changes in Microcystis aeruginosa as a result of interactions with heterotrophic bacteria

1. To reveal the role of aquatic heterotrophic bacteria in the process of development of Microcystis blooms in natural waters, we cocultured unicellular Microcystis aeruginosa with a natural Microcystis‐associated heterotrophic bacterial community. 2. Unicellular M. aeruginosa at different initial cell densities aggregated into colonies in the presence of heterotrophic bacteria, while axenic Microcystis continued to grow as single cells. The specific growth rate, the chl a content, the maximum electron transport rate (ETR_max) and the synthesis and secretion of extracellular polysaccharide (EPS) were higher in non‐axenic M. aeruginosa than in axenic M. aeruginosa after cell aggregation, whereas axenic and non‐axenic M. aeruginosa displayed the same physiological characteristic before aggregation. 3. Heterotrophic bacterial community composition was analysed by PCR–denaturing gradient gel electrophoresis (PCR–DGGE) fingerprinting. The biomass of heterotrophic bacteria strongly increased in the coinoculated cultures, but the DGGE banding patterns in coinoculated cultures were distinctly dissimilar to those in control cultures with only heterotrophic bacteria. Sequencing of DGGE bands suggested that Porphyrobacter, Flavobacteriaceae and one uncultured bacterium could be specialist bacteria responsible for the aggregation of M. aeruginosa. 4. The production of EPS in non‐axenic M. aeruginosa created microenvironments that probably served to link both cyanobacterial cells and their associated bacterial cells into mutually beneficial colonies. Microcystis colony formation facilitates the maintenance of high biomass for a long time, and the growth of heterotrophic bacteria was enhanced by EPS secretion from M. aeruginosa. 5. The results from our study suggest that natural heterotrophic bacterial communities have a role in the development of Microcystis blooms in natural waters. The mechanisms behind the changes of the bacterial community and interaction between cyanobacteria and heterotrophic bacteria need further investigations.     

Effects of the blue-green alga Microcystis aeruginosa on zooplankton competitive relations

Summary Field distribution patterns and laboratory feeding experiments have suggested that blooms of colonial blue-green algae strongly inhibit relatively large-bodied daphnid cladocerans. We conducted laboratory experiments to test the hypothesis that blooms of the colonial blue-green alga Microcystis aeruginosa would shift competitive dominance away from large-bodied daphnid cladocerans toward smaller-bodied cladocerans, copepods, and rotifers. In laboratory competition experiments, increasing the proportion of M. aeruginosa in the algal food supply resulted in a shift from dominance by the relatively largebodied cladoceran Daphnia ambigua to dominace by the copepod Diaptomus reighardi. The small-bodied cladoceran Bosmina longirostris was always numerically heavily dominant over D. ambigua, but its estimated population biomasses were only slightly higher than those of D. ambigua. Daphnia ambigua consistently outcompeted the rotifer Brachionus calyciflorus. Our results demonstrate that blooms of M. aeruginosa can alter zooplankton competitive relations in laboratory experiments, favoring small-bodied cladocerans and copepods at the expense of large-bodied cladocerans. However, contrary to predictions, blooms of M. aeruginosa did not improve the competitive ability of rotifers.     

Effects of Microcystis aeruginosa on interference competition between Daphnia pulex and Keratella cochlearis

Laboratory experiments tested the hypothesis that a toxic strain of Microcystis aeruginosa decreases the ability of Daphnia pulex to interfere with Keratella cochlearis. To test a variety of conditions, juvenile and adult Daphnia were exposed to the cyanobacterium for different time periods prior to, and during the experiments. Adult Daphnia not only suppressed rotifers over successive two-day intervals, but also had a significant impact within a 24-hour period. However, the presence of Microcystis (5 × 105 cells ml^–1) decreased the Daphnia effect in both experiments. Although juvenile Daphnia also significantly suppressed Keratella population growth, the presence of Microcystis (10⁵ and 5 × 10⁵ cells ml^–1) caused a significant reduction in daphniid body size and decreased the ability of both nonacclimated and acclimated daphniids to suppress rotifers. Keratella inhalation and mortality are positively correlated with filtering rates and body size of Daphnia. Therefore, the feeding rates and size structure of a Daphnia population will determine its potential to interfere with vulnerable rotifers. In all experiments the presence of Microcystis significantly decreased the ability of Daphnia to interfere with this rotifer despite the fact that Keratella was also inhibited. In the field this effect might be augmented if Microcystis colonies are more easily ingested by cladocerans than by the rotifers.     

Population dynamics and production of cladoceran zooplankton in the highly eutrophic Lake Kasumigaura

The growth rate, birth rate, death rate and production of the cladocera of Lake Kasumigaura were studied. Standing crop of zooplankton seemed to be governed by predation rather than food. Maximum productivity of cladocerans was observed in late August and early September. There were differences in production between sampling stations. The highest production was recorded in the most eutrophic basin, where heavy water blooms of Microcystis aeruginosa occurred. Maximum secondary production coincided with maximum primary production, which was mainly due to M. aeruginosa. Cladocerans probably utilize decomposed or decomposing Microcystis cells and bacteria in summer. Estimates of annual production of cladocerans varied from 4.2 to 13.1 g dry wt · m^–3, and annual P:B ratios ranged from 36 to 108. The production of cladocerans in Takahamairi Bay was 2.7% of gross primary production.     

富营养化山仔水库沉积物微囊藻复苏的受控因子

山仔水库作为福建省福州市重要的饮用水水源地之一,从2000年起每年都周期性爆发蓝藻门微囊藻属(Microcystis)水华现象,特别是在温暖的季节。对于这个富营养化水库,是否在沉积物中存在蓝藻门微囊藻的"种源"？假设山仔水库底泥中存在蓝藻门微囊藻休眠体,一定的环境条件能够促进蓝藻门微囊藻的复苏。研究于2009年12月采集水库大坝断面5根柱状沉积物,采用正交试验的方法,模拟了温度、光照、pH值、营养盐、物理扰动和浮游动物(膨大肾形虫)等环境因子对山仔水库沉积物中蓝藻门微囊藻的复苏响应。结果表明,底泥中存在着一定数量的底栖动物和硅藻、蓝藻和绿藻等微藻,从实验结束后沉积物中微囊藻数量的减少和上覆水体中微囊藻数量的增加,可以判断在适宜的环境条件下,蓝藻门微囊藻能够复苏并上浮到上覆水体中。正交实验显著性分析表明,温度是沉积物蓝藻门微囊藻复苏的重要影响因子,光照次之,上覆水体的pH值、营养盐、物理扰动和浮游动物干扰对沉积物蓝藻门微囊藻的复苏影响作用不显著,升温有利于沉积物中微囊藻的复苏。     

Grazing on toxic cyanobacterial blooms by tadpoles of edible frog Rana grylio

Tadpoles of Rana grylio were raised as edible frogs in fishponds of Guanqiao in Wuhan City, Hubei, China, during cyanobacterial blooms from June to October. The dominant cyanobacterial species was Microcystis, which was found to be lethally toxic by intraperitoneal (i.p.) mouse bioassay. Little is known about the effect of tadpoles on toxic cyanobacterial blooms. To evaluate the potential of the tadpoles to graze on cyanobacterial blooms, the tadpoles were fed on Microcystis collected from the field in the laboratory. The Microcystis cells decreased from 1.19 × 10⁷ cells mL^?1 to 3.23 × 10⁶ cells mL^?1, with a sharp reduction of 73% of the initial Microcystis population observed in the first 24 h after introduction of the tadpoles. The ponds containing tadpoles had a markedly lower density of Microcystis than those lacking tadpoles. Tadpoles exposed to either cultured Microcystis aeruginosa (NIES–90, 2.768 µg microcystins mg^–1 dw^–1) cells or lysed M. aeruginosa cells grew well, however, indicating that they were unaffected by Microcystis toxins. We found a significant increase in tadpole body weight after feeding on either field Microcystis or cultured M. aeruginosa. The mean increase in individual body weight was 20 mg day^?1 when fed on Microcystis from the pond, and 7 mg day^?1 when fed on M. aeruginosa from culture. Our study strongly suggested that there is a direct trophic relationship between R. grylio tadpoles and toxic Microcystis blooms and they possess the potential to graze on toxic Microcystis. The results imply that R. grylio tadpoles may play an important ecological role in reducing toxic cyanobacterial blooms caused by Microcystis.     

Variation in life history responses of Daphnia to toxic Microcystis aeruginosa

Three clones of Daphnia pulex and two clones of Daphnia longispinawere exposed to toxic Microcystis aeruginosa for 21 days ina lifetable experiment. The growth and reproduction of individualdaphnids were followed daily to study the long-term effectsof toxic Microcystis. Exposure to Microcystis increased mortality,decreased growth, delayed maturation and decreased offspringproduction, indicating nutritional deficiency and toxic effects.We found variation in life history responses between speciesand among clones. Our results suggest that toxic cyanobacteriamay act as a modifying agent in zooplankton communities at boththe species and clonal level.     

Influence of toxic and non-toxic phytoplankton on feeding and survival of Dreissena polymorpha (Pallas) larvae

Grazing and survival of larvae of the zebra mussel, Dreissena polymorpha, on a green alga and cyanobacteria were studied in laboratory experiments. Clearance rates of the larvae were determined for Chlamydomonas reinhardtii (green alga), two non-toxic and two toxic Microcystis aeruginosa strains (Cyanobacteria). Clearance rates of larvae on non-toxic Microcystis were significantly higher than on toxic Microcystis. The clearance rate on Chlamydomonas reinhardtii was in between the clearance rates on toxic and non-toxic Microcystis strains and not significantly different from them. Effects of toxicity of Microcystis on the survival of zebra mussel larvae was investigated in a short-term experiment. Survival of larvae fed toxic Microcystis was lower than that of larvae fed non-toxic Microcystis, but higher than that of starved larvae. This may imply that, for survival of zebra mussel larvae, it is better to have bad quality (toxic) food than no food.     

Grazing on <Emphasis Type="Italic">Microcystis</Emphasis> (Cyanophyceae) by testate amoebae with special reference to cyanobacterial abundance and physiological state

We examined the growth of testate amoebae preying on Microcystis whose physiological states were different in laboratory experiments and a hypertrophic pond. We prepared three experimental systems using water samples dominated by Microcystis aeruginosa: light incubation (control), dark incubation (dark), and light incubation with addition of nitrogen and phosphorus (+NP). In all the systems, the colony density of M. aeruginosa decreased slightly during incubation. Physiological activity of phytoplankton as determined by chlorophyll fluorescence was high and almost constant in the control and +NP systems, whereas it decreased in the dark system. Cell densities of testate amoebae increased in the control and +NP systems, whereas in the dark system they remained low. Thus, growth of the amoebae was low in the systems where physiological activity of Microcystis was low. In a hypertrophic pond, cell density of testate amoebae increased and remained high when M. aeruginosa predominated. Cell density of testate amoebae increased remarkably, simultaneously with the increases in M. aeruginosa colony density and phytoplankton physiological activity. We also found a significant correlation between densities of M. aeruginosa colonies and testate amoebae. We suggested that the physiological activity of Microcystis is one important factor affecting the growth of testate amoebae grazing on Microcystis.     

The importance of morphological versus chemical defences for the bloom-forming cyanobacterium Microcystis against amoebae grazing

Amoebae grazing can be an important loss factor for blooms of the common cyanobacterium Microcystis. Some Microcystis strains seem to be protected against amoebae grazing, but it is unclear whether this is achieved by their colony morphology or biochemically. These factors were investigated in grazing experiments using two Microcystis-grazing amoebae (Korotnevella sp. and Vannella sp.) and two Microcystis strains with differing colony morphology (aeruginosa and viridis morphotype) and different sensitivity to amoebae grazing. Amoebae did not increase in density and failed to reduce the growth rate of cultures of the amoebae insensitive viridis strain, irrespective of whether the Microcystis strain was colonial or unicellular. This suggests that the extended mucilage matrix surrounding viridis colonies is not the main defence mechanism against amoebae grazing. At the same time, the growth rate of both unicellular and colonial cultures of the amoebae-sensitive aeruginosa strain was heavily reduced by the growing amoebae. The addition of filtered viridis-conditioned medium to aeruginosa cultures significantly decreased both amoebae growth and its effect on aeruginosa growth rates, which indicates that extracellular compounds constitutively produced by viridis are at least partially responsible for their insensitivity to amoebae grazing. These results demonstrate the potential importance of chemical interactions between lower trophic levels (protists) for Microcystis bloom dynamics.     

Growth interactions among blue-green (Anabaena Oscillarioides,Microcystis aeruginosa) and green (Chlorella sp.) algae

The growth interactions amongst the blue-green algal species Anabaena oscillarioides, Microcystis aeruginosa and the green alga, Chlorella sp. were studied both in mixed cultures and in filter cultures separated by a membrane filter in the two arms of an interaction U-tube. The role of nutrients especially phosphate upon the interaction has also been studied. Anabaena and Microcystis both inhibited the growth of Chlorella while Microcystis also inhibited the growth of Anabaena. The inhibitory effect of Microcystis was found to be dependent on high concentrations of the initial algal inocula and independent of the initial concentration of nutrients such as inorganic phosphate, indicating that the nature of the inhibition is probably due to the production of inhibitory extracellular products by Microcystis. On the other hand, the inhibitory effect of Anabaena on Chlorella is the consequence of nutrient competition with Anabaena competing more effectively for the available phosphate.     

Toxin production of cyanobacteria is increased by exposure to zooplankton

1. Cyanobacterial toxin production in response to direct and indirect zooplankton feeding activity was examined using four strains of Microcystis aeruginosa, of which three were previously reported to be toxic to zooplankton and one non‐toxic. Direct (Microcystis cultured with zooplankton) and indirect effects (Microcystis cultured with filtered zooplankton culture media, ZCMF) were tested for the zooplankton species, Moina macrocopa, Daphnia magna or D. pulex. 2. With direct exposure to zooplankton, increased mass‐specific microcystin productions occurred in all Microcystis strains, with mean microcystin concentrations up to five times greater (61.5–177.3 μg g^?1 dry cell) than the controls. 3. With indirect exposure, mass‐specific microcystin production increased over controls in three strains of M. aeruginosa. Mean maximum concentrations of microcystin during the experiment were 92.6–125.7 μg g^?1 dry cell. 4. These results suggest that several strains of Microcystis aeruginosa increased toxin production in response to direct and indirect exposure to herbivorous zooplankton of several species, and support the hypothesis that this response is an induced defence mediated by the release of info‐chemicals from zooplankton.     

Investigations on the relationships between algal blooms and bacterial populations in the Schlei Fjord (western Baltic Sea)

Summary 1. Investigations were carried out on monthly voyages to the Schlei, a fjord of the western Baltic Sea, from 1972 to 1974.2. The Schlei is characterized by two successive water blooms — one in the spring caused byChlorella sp., and a Cyanophyceae bloom in late summer withMicrocystis aeruginosa as the dominant species.3. The blooms are accompanied by different bacteria populations. It was noted, e. g., that the proportion of red pigmented bacteria is greatest during the spring, whereas in late summer the numbers of pigmented bacteria decrease and white or colorless forms dominate.4. In order to determine the relationship of the bacteria to the phytoplankton blooms, the predominant algae and bacteria species in the Schlei were isolated, and laboratory experiments with these microorganisms were carried out.5. The results of these experiments showed that the growth of the red bacteria was clearly enhanced when cultivated together withChlorella sp.6. The enhancement takes place immediately with actively growingChlorella cultures. Apparently these algae secrete organic substances into the culture medium during their exponential phase of growth, which are utilized by the red bacteria. It is likely that a similar process occurs in the Schlei. The rapid increase in red bacteria has been shown to take place parallel to the development of theChlorella water bloom in the spring. The proportion of pigmented bacteria decreases in the late summer with the breakdown of theChlorella bloom, and a new bacterial population becomes dominant.7. Other experiments withChlorella sp. showed thatEscherichia coli is strongly inhibited by the presence of these algae. The inhibition takes place only afterChlorella has reached the end of the exponential phase of growth, however. The inhibitory substances are probably autolysis or degradation products which accumulate in the culture medium during the stationary phase of algal growth.8. None of the bacteria tested had any influence on the growth rate ofChlorella sp., nor were the algae cells colonized by bacteria at any time.9. With the development of theMicrocystis bloom in late summer, white or colorless bacteria are more frequently found in the waters of the Schlei. At the same time, there is generally a decrease in the saprophyte counts including pigmented bacteria.10. Two strains of white bacteria commonly associated withMicrocystis were able to suppress the growth of many other bacteria on agar plates, especially red, yellow and brown pigmented species.11. Sterile filtrates prepared from the culture solutions of the white bacteria had no effect on the strains tested, however. The suppression on agar plates is therefore more likely due to competition for nutrients. There is no evidence that antibiotic substances are involved.12. Filtrates prepared from non-axenic cultures ofMicrocystis aeruginosa during the exponential as well as stationary phase of growth also did not inhibit the growth of the bacteria tested.13. The decrease in the numbers of saprophytic bacteria in the Schlei during the summer may be due in part to the presence of the large white colonies on agar plates which prevent other bacteria from developing. These white bacteria are apparently associated withMicrocystis water blooms; possibly a symbiotic or mutualistic relationship exists between these microorganisms.

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Untersuchungen über die Beziehungen zwischen Algenblüten und Bakterienpopulationen in der Schlei (westliche Ostsee)

Kurzfassung Die Wechselbeziehungen zwischen Algenblüten und Bakterien wurden in der Schlei, einer Förde der westlichen Ostsee, untersucht. Die Wasserblüten, im Frühjahr vonChlorella spec. und im Spätsommer vonMicrocystis aeruginosa gebildet, werden von Änderungen in den Bakterienpopulationen begleitet. Laborversuche wurden durchgeführt mit den hauptblütenbildenden Algenarten und den dominanten Bakterienarten. Die Ergebnisse zeigen, daß das Wachstum von einigen rotpigmentierten Bakterien(Flavobacterium), die die Wasserblüte vonChlorella begleiten, durch Stoffe, die von den Algen in der logarithmischen Wachstumsphase in das Medium abgegeben werden, gefördert wird.Microcystis aeruginosa wird von mindestens zwei chitinabbauenden Bakterienarten (darunterPseudomonas spec.) begleitet. Die ökologischen Zusammenhänge werden diskutiert.

     

Isolation and characterization of microcystin producing Microcystis from a Central Indian water bloom

Microcystis aeruginosa Kütz, a well-known microcystin (hepatotoxin) producing cyanobacterium was the dominant bloom-forming organism in a mesotrophic lake at Nagpur in Central India, which was isolated and characterized for morphospecies and microcystin content. Compact spherical colonies, formation of daughter colonies, and clathration of older colonies leading to release of solitary cells, were characteristics of laboratory grown M. aeruginosa. Its growth, monitored as increase in optical density (OD) measured at 678 nm (the wavelength selected using dilution curve technique), exhibited a maximum specific growth rate (μ_max) of 0.34 day⁻¹ which, was attained on the 5th day of the experiment with a doubling time of 3.25 days. Though the morphological characters of the M. aeruginosa under field conditions were not retained under laboratory conditions, the microcystin content and type of variants did match with bloom samples. Reverse phase high performance liquid chromatography (RP-HPLC) analyses revealed that the laboratory grown isolate of Microcystis produced microcystin-RR (732 μg g⁻¹ dry weight biomass) and demethylated microcystin-RR (165 μg g⁻¹ dry weight biomass) variants, which are reported to be less toxic when compared to microcystin-LR. LC/ESI/MS further confirmed the presence of these two variants. Geographical distribution of microcystin variants and their prevailing concentrations need to be considered during formulation of guideline values for drinking and recreational waters.     

Determination of Oligopeptide Diversity within a Natural Population of Microcystis spp. (Cyanobacteria) by Typing Single Colonies by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

Besides the most prominent peptide toxin, microcystin, the cyanobacteria Microcystis spp. have been shown to produce a large variety of other bioactive oligopeptides. We investigated for the first time the oligopeptide diversity within a natural Microcystis population by analyzing single colonies directly with matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS). The results demonstrate a high diversity of known cyanobacterial peptides such as microcystins, anabaenopeptins, microginins, aeruginosins, and cyanopeptolins, but also many unknown substances in the Microcystis colonies. Oligopeptide patterns were mostly related to specific Microcystis taxa. Microcystis aeruginosa (Kütz.) Kütz. colonies contained mainly microcystins, occasionally accompanied by aeruginosins. In contrast, microcystins were not detected in Microcystis ichthyoblabe Kütz.; instead, colonies of this species contained anabaenopeptins and/or microginins or unknown peptides. Within a third group, Microcystis wesenbergii (Kom.) Kom. in Kondr., chiefly a cyanopeptolin and an unknown peptide were found. Similar patterns, however, were also found in colonies which could not be identified to species level. The significance of oligopeptides as a chemotaxonomic tool within the genus Microcystis is discussed. It could be demonstrated that the typing of single colonies by MALDI-TOF MS may be a valuable tool for ecological studies of the genus Microcystis as well as in early warning of toxic cyanobacterial blooms.     

Dual Roles of Cadaverine-Producing Pseudomonas sp. on Microcystis spp. in Hyper-Eutrophic Water

A bacterium isolated from Lake Taihu was identified as Pseudomonas sp. A3CT, which performed different effects on Microcystis spp. Growth of Microcystis flos-aquae and Microcystis aeruginosa was assessed in co-culture with A3CT to determine the stimulatory or inhibitory effects on these toxic, bloom-forming Microcystis strains. Results demonstrated that the impacts of A3CT were species specific. A3CT promoted the growth of M. aeruginosa but inhibited growth of M. flos-aquae. To investigate the cause of this phenomenon, the chemical composition of A3CT exudates and the impact of exposure to A3CT exudates on the two Microcystis species were determined. Results suggested that the observed differential growth responses of the two microalgae to A3CT exposure might be related to two components in A3CT exudates NH₄ ⁺ and cadaverine. Growth stimulation of M. aeruginosa by A3CT was significantly related to NH₄ ⁺ concentration. Cadaverine possibly acted as a growth inhibitor of M. flos-aquae. The different effects of cadaverine on growth of the two Microcystis strains suggested that A3CT might play a role in intrageneric succession patterns observed during Microcystis blooms in Lake Taihu.     

Effect of mixed diets (cyanobacteria and green algae) on the population growth of the cladocerans <Emphasis Type="Italic">Ceriodaphnia dubia</Emphasis> and <Emphasis Type="Italic">Moina macrocopa</Emphasis>

Microcystis aeruginosa, a cosmopolitan form, is a colonial cyanobacterium, which is also common in many freshwater bodies in Mexico. In eutrophic water bodies cyanobacteria are often the main phytoplankton that co-exist with cladocerans. We evaluated the effect of mixed diets, comprising 0, 25, 50, 75, and 100% on dry weight basis of M. aeruginosa, and the rest of one of two green algal species (Chlorella vulgaris and Scenedesmus acutus), on the population growth of the cladocerans Ceriodaphnia dubia and Moina macrocopa. Regardless of the share of M. aeruginosa in the mixed diet, C. dubia fed Chlorella had a longer initial lag phase. However, in mixed diet with S. acutus, the lag phase of C. dubia increased with increasing proportion of M. aeruginosa. When raised on 100% M. aeruginosa, the population growth of C. dubia was lowered compared with 100% S. acutus or 100% C. vulgaris. Increased proportion of M. aeruginosa in the mixed diet also resulted in decreased abundance of M. macrocopa. Irrespective of diet type, M. macrocopa had a shorter lag phase than C. dubia. Depending on the diet type, the rate of population increase (r) of C. dubia varied from 0.07 to 0.26 d⁻¹ while that of M. macrocopa was higher (0.14–0.61 d⁻¹). For both cladoceran species, the lower r values were obtained when fed Microcystis. Our study showed that the strain of M. aeruginosa was not highly toxic to cause total elimination of either C. dubia or M. macrocopa. Addition of a green algal component to the diet improved the population growth rates of both cladoceran species.