Morphological,biochemical and phylogenetic assessments of water‐bloom‐forming tropical morphospecies of Microcystis (Chroococcales,Cyanobacteria)

Previous polyphasic analyses of five morphospecies of the water‐bloom‐forming cyanobacterial genus Microcystis, Microcystis aeruginosa (Kützing) Lemmermann (=Microcystis aeruginosa (Kützing) Kützing), Microcystis ichthyoblabe Kützing, Microcystis novacekii (Komárek) Compère, Microcystis viridis (A. Braun) Lemmermann, and Microcystis wesenbergii (Komárek) Komárek in Kondratieva, have shown them to be conspecific and they have been proposed to be included under the binomial Microcystis aeruginosa (Kützing) Lemmermann. However, several morphospecies from tropical regions, such as Microcystis bengalensis Banerji, Microcystis panniformis Komárek, Komárková‐Legnerová, Sant'anna, Azevedo & Senna, Microcystis protocystis Crow, Microcystis pseudofilamentosa Crow, Microcystis ramosa Bharadwaya, and Microcystis robusta (Clark) Nygaard, have never been analyzed biochemically or phylogenetically; consequently, their taxonomic status is uncertain. To resolve this issue, we collected 57 strains of Microcystis from Vietnam for taxonomic analysis using a polyphasic approach. Strains were assigned to the six tropical morphospecies listed above or to four morphospecies with cosmopolitan distributions (M. aeruginosa, M. ichthyoblabe, M. novacekii, and M. wesenbergii). Several strains produced colony variants in different culture media; some of these variants had forms that overlapped with those of other morphospecies. Cell diameters varied widely between strains (2.6–9.3 µm) and were unrelated to morphospecies discrimination criteria. Strains of the 10 morphospecies examined had similar fatty acid compositions and closely similar 16S rRNA gene sequences (>99.2% similar). Phylogenetic analyses using 16S rRNA gene and 16S–23S internal transcribed spacer sequences did not identify any clear separations corresponding to morphospecies concepts or microcystin‐producing abilities. Thus, the six tropical morphospecies (M. bengalensis, M. panniformis, M. protocystis, M. pseudofilamentosa, M. ramosa, and M. robusta) are not natural taxonomic units within the genus Microcystis and should be included under M. aeruginosa.     

MEASUREMENT OF IN SITU SPECIFIC GROWTH RATES OF MICROCYSTIS (CYANOBACTERIA) FROM THE FREQUENCY OF DIVIDING CELLS1

Diel changes in the frequency of dividing cells (FDC) of three Microcystis species were investigated in a small eutrophic pond from July to October 2005. The representative species was M. aeruginosa (Kütz.) Kütz., constituting 57%–86% of the Microcystis population throughout the study period, and the remainder were M. viridis (A. Braun) Lemmerm. and M. wesenbergii (Komárek) Komárek. The FDC of M. aeruginosa and M. wesenbergii increased in the daytime and fell in the nighttime in July and August, but this regular variation was not observed in September or October. The in situ specific growth rates of Microcystis species were estimated based on the assumption that the specific growth rate can be given as an absolute value of the derivative of FDC with respect to time. The calculated values were similar among species—0.15–0.38 · d^?1 for M. aeruginosa, 0.14–0.63 · d^?1 for M. viridis, and 0.18–0.61 · d^?1 for M. wesenbergii. The specific growth rates in July and August slightly exceeded those in September and October. The analysis of the in situ specific growth rate of Microcystis indicated that recruitment of the benthic population or morphological change, rather than massive growth, was at least partly responsible for the dominance of M. aeruginosa in the study pond.     

Toxic cyanobacteria (blue-green algae) in Finnish fresh and coastal waters

A survey of the occurrence of toxic blooms of cyanobacteria in Finnish fresh and coastal waters was made during 1985 and 1986. Toxicity of the freeze-dried water bloom samples was tested by mouse-bioassay (i.p.). Forty-four per cent (83/188) of the bloom samples were found to be lethally toxic. Hepatotoxic blooms (54) were almost twice as common as neurotoxic ones (29). Anabaena was the most frequently found genus in toxic and non-toxic blooms and it was present in all neurotoxic samples. Statistical associations were found between hepatotoxicity and incidence of Microcystis aeruginosa, M. viridis, M. wesenbergii, Anabaena flos-aquae and Anabaena spiroides. Neurotoxicity was statistically associated with Anabaena lemmermannii, Anabaena flos-aquae and Gomphosphaeria naegeliana. Isolation of strains of cyanobacteria confirmed the occurrence of hepatotoxic and neurotoxic strains of Anabaena, as well as hepatotoxic strains of Microcystis and Oscillatoria species.Toxic blooms caused cattle poisonings at three different lakes during the study period. Toxic blooms also occurred in drinking water sources. Our study shows that toxic cyanobacteria are more common in Finnish lakes than would be expected on the basis of animal poisonings. The results of this study show the existence of toxic cyanobacteria in Finnish water supplies and the need for their continued study as agents of water based disease.     

GENETIC VARIABILITY OF BRAZILIAN STRAINS OF THE MICROCYSTIS AERUGINOSA COMPLEX (CYANOBACTERIA/CYANOPHYCEAE) USING THE PHYCOCYANIN INTERGENIC SPACER AND FLANKING REGIONS (cpcBA)

The genetic and morphological variability among 15 Brazilian strains of Microcystis aeruginosa (Kütz.) Kütz. collected from four locations was examined and compared with several reference strains of M. aeruginosa , M. viridis (A. Br.) Lemm. and M. wesenbergii (Kom.) Kom. in Kondr. Brazilian strains were classified by morphological features and by comparison of the nucleotide sequences of the cpc BA intergenic spacer and flanking regions. Our results indicate that Brazilian strains classified as M. aeruginosa are phylogenetically diverse compared with reference strains of M. aeruginosa and that the current taxonomy underestimates genetic diversity within M. aeruginosa. The data also demonstrate that morphological criteria alone are inadequate to characterize Microcystis species. Although colonial characters were shown to vary considerably in culture, some genetic lineages demonstrated consistent cellular diameter ranges, indicating that cell size has value as a taxonomic character. The detection of six M. aeruginosa genotypes in a single water body indicates that morphological approaches can also seriously underestimate the diversity of Microcystis bloom populations.     

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.     

Morphological variability of colonies of Microcystis morphospecies in culture

Serial observations were carried out on cultures of five morphospecies of the genus Microcystis Kützing ex Lemmermann 1907, Microcystis aeruginosa (Kützing) Kützing, Microcystis ichthyoblabe Kützing, Microcystis novacekii (Komárek) Compére, Microcystis viridis (A. Brown) Lemmermann, and Microcystis wesenbergii (Komárek) Komárek in Kondratieva. Many strains maintained colony forms characteristic of their morphospecies, and others showed morphological variations, some of which were characteristic of other morphospecies. M. novacekii displayed several morphotypes including some characteristics of M. aeruginosa and M. ichthyoblabe. M. wesenbergii also showed great morphological variability and showed morphotypes characteristic of M. aeruginosa. Distinction among these morphospecies, therefore, seemed to be obscure or impossible. We conclude that the current classification of the genus Microcystis, chiefly based on morphological characteristics, is no longer valid and must be reviewed in light of our observations that one strain may have various colony forms.     

The mechanism of competition between two bloom‐forming Microcystis species

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Morphospecies and genospecies of Microcystis during blooms in eutrophic Lake Taihu (China) in autumn

Microcystis colonies collected in a hypertrophic lake (Lake Taihu, China) in October and November 2012 were divided into five subsamples according to colony size (<75, 75–150, 150–300, 300–500, and >500 μm). All the subsamples collected in November were dominated with Microcystis ichthyoblabe and the percentages of M. ichthyoblabe exceeded 83%. The percentages of Microcystis aeruginosa of the subsamples in >500 μm class collected in October was 93.5%. For the sample collected in October, the percentage of M. ichthyoblabe was more than 58% in <75, 75–150, 150–300 μm classes. The 16S rDNA as well as some polysaccharide biosynthesis-related genes were analyzed to understand the phylogeny of Microcystis species. There was no variant site presented in each Microcystis subsample but a single nucleotide polymorphism (SNP) was found in 16S rDNA alignment tested using MSR1 in subsamples between the two months in the current study. Our results also showed that samples collected in two months can by divided into two parts by the phylogenetic analysis using two polysaccharide biosynthesis-related genes (espL and TagH). All the results suggested that 16S rDNA was valuable to identify seasonal succession of Microcystis genospecies and the diversity of Microcystis morphospecies would be explained by these polysaccharide biosynthesis-related genes.     

Colony formation in the cyanobacterium Microcystis

Morphological evolution from a unicellular to multicellular state provides greater opportunities for organisms to attain larger and more complex living forms. As the most common freshwater cyanobacterial genus, Microcystis is a unicellular microorganism, with high phenotypic plasticity, which forms colonies and blooms in lakes and reservoirs worldwide. We conducted a systematic review of field studies from the 1990s to 2017 where Microcystis was dominant. Microcystis was detected as the dominant genus in waterbodies from temperate to subtropical and tropical zones. Unicellular Microcystis spp. can be induced to form colonies by adjusting biotic and abiotic factors in laboratory. Colony formation by cell division has been induced by zooplankton filtrate, high Pb²⁺ concentration, the presence of another cyanobacterium (Cylindrospermopsis raciborskii), heterotrophic bacteria, and by low temperature and light intensity. Colony formation by cell adhesion can be induced by zooplankton grazing, high Ca²⁺ concentration, and microcystins. We hypothesise that single cells of all Microcystis morphospecies initially form colonies with a similar morphology to those found in the early spring. These colonies gradually change their morphology to that of M. ichthyoblabe, M. wesenbergii and M. aeruginosa with changing environmental conditions. Colony formation provides Microcystis with many ecological advantages, including adaption to varying light, sustained growth under poor nutrient supply, protection from chemical stressors and protection from grazing. These benefits represent passive tactics responding to environmental stress. Microcystis colonies form at the cost of decreased specific growth rates compared with a unicellular habit. Large colony size allows Microcystis to attain rapid floating velocities (maximum recorded for a single colony, ∼ 10.08 m h⁻¹) that enable them to develop and maintain a large biomass near the surface of eutrophic lakes, where they may shade and inhibit the growth of less‐buoyant species in deeper layers. Over time, accompanying species may fail to maintain viable populations, allowing Microcystis to dominate. Microcystis blooms can be controlled by artificial mixing. Microcystis colonies and non‐buoyant phytoplankton will be exposed to identical light conditions if they are evenly distributed over the water column. In that case, green algae and diatoms, which generally have a higher growth rate than Microcystis, will be more successful. Under such mixing conditions, other phytoplankton taxa could recover and the dominance of Microcystis would be reduced. This review advances our understanding of the factors and mechanisms affecting Microcystis colony formation and size in the field and laboratory through synthesis of current knowledge. The main transition pathways of morphological changes in Microcystis provide an example of the phenotypic plasticity of organisms during morphological evolution from a unicellular to multicellular state. We emphasise that the mechanisms and factors influencing competition among various close morphospecies are sometimes paradoxical because these morphospecies are potentially a single species. Further work is required to clarify the colony‐forming process in different Microcystis morphospecies and the seasonal variation in this process. This will allow researchers to grow laboratory cultures that more closely reflect field morphologies and to optimise artificial mixing to manage blooms more effectively.     

DIGESTION OF MICROCYSTIS AERUGINOSA BY OREOCHROMIS MOSSAMBICUS

SUMMARY

The mean assimilation efficiency of aquarium acclimatized Oreochromis mossambiaue fed on a diet of Microcystis aeruginosa collected from Hartbeespoort Dam was determined as 50,8% for total organic matter, 63,7% for protein and 75,5% for phosphorus. Transmission electron microscopic examination of faeces of fish fed on M. aeruginosa, revealed that most Microcystis cell walls had become permeable allowing cell contents to leach out. Further digestion resulted in the break down of the cell wall structure. Up to 25% of the cells, however, appeared intact after passing through the fish. Fish fed on a diet of M. aeruginosa lost mass initially, but after 21 days showed a slight gain in mass. The high protein content of M. aeruginosa nay have inhibited efficient metabolism and would have led to reduced growth in fish.     

Application of the frequency of dividing cells technique to estimate the in situ growth rate of Microcystis (Cyanobacteria)

1. Diel patterns of the frequency of dividing cells (FDC) of the bloom‐forming cyanobacteria Microcystis were investigated using both culture strains and natural populations. 2. In laboratory experiments, diel division cycles were examined twice in a 24‐h light/dark cycle during time‐course batch incubations of six culture conditions using two strains (morphospecies) of Microcystis (M. aeruginosa and M. wesenbergii). While both strains clearly showed phased cell division in the light period during the logarithmic growth phase, the peaks of FDC became unclear towards the stationary phases. Some dividing cells were always found in the dark period regardless of whether or not division had paused at the same time. 3. This result implied the inadequacy of applying the model of McDuff & Chisholm [Limnology and Oceanography (1982) vol. 27 , pp. 783–787] directly to calculate the duration of cell division. Modified equations are proposed to calculate the duration of cytokinesis as a terminal event, in which the FDC values at night are regarded as 0% and all FDC values are subtracted by the minimum FDC value. 4. The diel FDC in natural populations of M. aeruginosa and M. wesenbergii were examined at five sites from a harbour to several distances offshore in Lake Biwa. While both species showed phased cell division patterns in the daytime at the harbour, no peaks in FDC were discernible in the samples taken from the offshore sites. These results strongly suggested that Microcystis growth was higher inshore than offshore. The in situ growth rates were estimated using the new equations.     

GENETIC CHARACTERIZATION OF STRAINS OF CYANOBACTERIA USING PCR-RFLP OF THE cpcBA INTERGENIC SPACER AND FLANKING REGIONS1

Oligonucleotide primers, specific for conserved regions of the genes encoding the β- and α-phycocyanin subunits of phycobilisomes (cpcB and cpcA) of cyanobacteria, were used to amplify a DNA fragment containing the intervening intergenic spacer region (cpcBA-IGS) of 19 strains of three morphospecies of cyanobacteria. Six Australian strains were identified as Anabaena circinalis Rabenhorst, six strains were identified as Microcystis aeruginosa Kützing, and seven strains were identified as Nodularia spumigena Mertens. Restriction enzyme digestion of the amplification products from the strains revealed restriction fragment length polymorphism (RFLP) within all three morphospecies. Strains corresponding to M. aeruginosa were highly polymorphic: 11 of the 14 restriction enzymes used displayed RFLPs. The A. circinalis and N. spumigena strains were less variable: three of 14 enzymes and seven of 14 enzymes, respectively, showed RFLPs. The presence of genetic variation between strains within these three divergent morphospecies, which span two orders of cyanobacteria (Chroococcales Wettstein and Nostocales (Borzi) Geitler), show that the cpcBA- IGS fragment has broad application as a molecular marker for intrageneric studies of cyanobacteria systematics and genetics.     

广州市景观湖微囊藻的分类学研究

于2008年3月至2009年4月,对广州市区若干景观湖水体的微囊藻属(Microcystis)进行分类学研究。共观察到11种微囊藻,分别是铜绿微囊藻(M. aeruginosa Kützing)、放射微囊藻(M. botrys Teiling)、坚实微囊藻(M. firma Kützing)、水华微囊藻(M. flosaquae Wittrock)、鱼害微囊藻(M. ichthyoblabe Kützing)、挪氏微囊藻(M. novacekii Komárek)、苍白微囊藻(M. pallida (Farlow) Lemm.)、假丝微囊藻(M. pseudofilamentosa Crow)、史密斯微囊藻(M. smithii Komárek & Anagnostidis)、绿色微囊藻(M. viridis A. Braun)和惠氏微囊藻(M. wesenbergii Komárek),对它们的形态学特征进行描述,并比较这些种类间的形态区别。     

DISTINCTIVE LECTIN LABELING OF THE FLAGELLAR APPARATUS OF TETRASELMIS (PRASINOPHYCEAE) AND DUNALIELLA (CHLOROPHYCEAE)1

Fluorescent labeling of the flagellar apparatus of Tetraselmis (Prasinophyceae) and Dunaliella (Polyblepharidaceae, Chlorophyceae) were successfully performed using fluorescein isothiocyanate–labeled lectins from Arachis hypogaea and Glycine maxima. These lectins specifically bound to the flagella and kinetosome of the cell but did not bind to the cell surface. Lectin binding on the flagellar apparatus remained constant under different culture media, temperatures, irradiances, cell division cycle, and culture aging. All the Tetraselmis and Dunaliella analyzed (five species, 20 clones) showed intense labeling of the flagellar apparatus. In contrast, no other species analyzed (46 clones of 25 species from four classes) showed binding to their flagellar apparatus. After the lectin treatment, many cells remained alive, and they were able to swim with the flagellar apparatus intensely labeled. The lectin binding indicates that the flagella and kinetosome of Tetraselmis are rich in Gal and GalNH₂ moieties and that the flagella of Dunaliella are rich in Gal and GalNAc moieties. Apparently, this feature seems to be specific to these species.     

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.     

CHANGES IN THE MORPHOLOGY AND POLYSACCHARIDE CONTENT OF MICROCYSTIS AERUGINOSA (CYANOBACTERIA) DURING FLAGELLATE GRAZING1

To investigate the changes in the morphology and polysaccharide content of Microcystis aeruginosa (Kütz.) Kütz. during flagellate grazing, cultures of M. aeruginosa were exposed to grazing Ochromonas sp. for a period of 9 d under controlled laboratory conditions. M. aeruginosa responded actively to flagellate grazing and formed colonies, most of which were made up of several or dozens of cells, suggesting that flagellate grazing may be one of the biotic factors responsible for colony formation in M. aeruginosa. When colonies were formed, the cell surface ultrastructure changed, and the polysaccharide layer on the surface of the cell wall became thicker. This change indicated that synthesis and secretion of extracellular polysaccharide (EPS) of M. aeruginosa cells increased under flagellate grazing pressure. The contents of soluble extracellular polysaccharide (sEPS), bound extracellular polysaccharide (bEPS), and total polysaccharide (TPS) in colonial cells of M. aeruginosa increased significantly compared with those in single cells. This finding suggested that the increased amount of EPS on the cell surface may play a role in keeping M. aeruginosa cells together to form colonies.     

Toxic Blue-green Algae Water Blooms Found in some Lakes in the German Democratic Republic

From 1977 to 1979 plankton samples were taken from 6 lakes in the German Democratic Republic (GDR) during water blooms and examined for their toxicity to homothermal animals. Microcystis aeruginosa, Aphanizomenon flos-aquae, Anabaena spiroides, and Oscillatoria redekei were dominant in the samples. With the exception of Oscillatoria redekei the algae tested had toxic effects on mice after intraperitoneal injection. The rate of survival of the test animals was particularly low when the algae were disintegrated by ultrasound or freeze-drying prior to injection, this indicating the endogenic character of the toxins. Water blooms of Microcystis aeruginosa taken from Lake Pehlitzsee (Eberswalde District) showed the highest toxicity with an LD₃₀ as high as 45 and 43.7 mg/kg, respectively. Injection of the lyophilized cells of Aphanizomenon flos-aquae brought about the same symptoms in the test animals as in the case of Microcystis, but the LD₃₀ was 200 mg/kg.     

UV-B radiation and phosphorus limitation interact to affect the growth,pigment content,and photosynthesis of the toxic cyanobacterium Microcystis aeruginosa

In this study, Microcystis aeruginosa was cultivated in a P-limited and P-replete culture medium and exposed to artificial UV-B radiation to investigate the interactive effect of UV-B exposure and phosphorus limitation on this harmful alga. After 15 days, both UV-B exposure and phosphorus limitation led to a significant decline in pigment content (phycocyanin and carotene) and photosynthetic activity (F _v/F _m and ETR_max), and the impact was most pronounced when the two conditions were combined. Due to the interactive effect, P-limited M. aeruginosa under UV-B exposure exhibited the lowest cell density compared to the other treatments. These results suggest that phosphorus limitation increases the stress of UV-B radiation in Microcystis. In other words, high-level UV-B radiation has higher growth inhibitory on Microcystis in P-limited lakes than in P-replete lakes.     

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.     

冲天湖底泥表层微囊藻休眠体复苏与菌群动态

对频繁暴发微囊藻水华的西洞庭冲天湖表层底泥和上覆水取样,检测和分析了底泥表层微囊藻休眠体丰度和菌浓度、上覆水中微囊藻细胞丰度和菌浓度以及部分理化性质,结合室内模拟试验。结果表明:2—6月份冲天湖底泥表层和上覆水中总菌浓度均显著上升(P0.05),底泥表层总菌浓度显著高于上覆水(P0.05),优势菌群均为微小杆菌属(Exiguobacterium)、假单胞菌属(Pseudomonas)和芽孢杆菌属(Bacillus);4月份底泥表层微囊藻休眠体开始复苏且休眠体丰度下降,6月份休眠体丰度显著低于4—5月份(P0.05),而上覆水中微囊藻细胞丰度上升,6月份显著高于4—5月份(P0.05);复苏优势藻为铜绿微囊藻(Microcystis aeruginosa)、水华微囊藻(Microcystis flos-aqua)和惠氏微囊藻(Microcystis wesenbergii);复苏期间促休眠体复苏优势菌群浓度显著上升、"底泥-上覆水"界面溶解氧浓度与TN/TP比显著下降(P0.05)。说明冲天湖底泥表层和上覆水优势菌群可能通过改变底泥表层理化环境影响微囊藻休眠体复苏。