Causative microorganisms for musty odor occurrence in the eutrophic Lake Kasumigaura

The musty odor phenomenon in Lake Kasumigaura, Japan (a eutrophic lake that is used for various purposes, including water supply source) was examined. The causative microorganisms responsible for the production of the odor compounds, geosmin and/or 2-methylisoborneol (MIB), and the odor release mechanism were studied in vitro and in situ. The numbers of the filamentous P. tenue in the lake water column were closely correlated with the concentration of MIB, but not geosmin. The isolated monoxenic P. tenue in culture produced only MIB. Geosmin concentration was well correlated with the number of actinomycetes in the sediment. Forty isolates of actinomycetes from the sediment around the water supply intake tower produced both geosmin and MIB in culture. Furthermore, the average ratio of production of geosmin to MIB was 1.40–1.0. Actinomycetes in the sediment played an important role in geosmin production. We concluded that geosmin and MIB from actinomycetes in the sediment, and MIB from P. tenue in the water column were jointly responsible for the severe musty odor occurrence of the waters supply source at Lake Kasumigaura.     

Dominant genera of cyanobacteria in Lake Taihu and their relationships with environmental factors

Cyanobacterial blooms in freshwaters have become one of the most widespread of environmental problems and threaten water resources worldwide. Previous studies on cyanobacteria in Lake Taihu often collected samples from one site (like Meiliang Bay or Zhushan Bay) and focused on the variation in patterns or abundance of Microcystis during the blooming season. However, the distribution of cyanobacteria in Lake Taihu shows differing pattern in various seasons. In this study, water samples were collected monthly for one year at five sites in Lake Taihu with different trophic status and a physicochemical analysis and denaturing gradient gel electrophoresis (DGGE) were conducted. DGGE fingerprint analysis showed that Microcystis (7/35 bands) and Synechococcus (12/35 bands) were the two most dominant genera present during the study period at all five sites. Cyanobium (3/35 bands) was the third most common genus which has seldom been previously reported in Lake Taihu. Redundancy analysis (RDA) indicated that the cyanobacterial community structure was significantly correlated with NO₃^--N, COD_Mn, and NH₄⁺-N in the winter and spring, whereas it was correlated with water temperature in the summer and autumn. Limiting the nutrient input (especially of N and C loading) in Lake Taihu would be a key factor in controlling the growth of different genera of cyanobacteria.     

Spatial and seasonal shifts in bloom‐forming cyanobacteria in Lake Chaohu: Patterns and driving factors

The patterns of spatial and temporal shifts in bloom‐forming cyanobacteria and the driving factors for these patterns were determined by analyzing the distribution of these cyanobacteria in Lake Chaohu using data from satellite images and field samples collected during 2012 and 2013. The cyanobacterial blooms primarily occupied the western region of Lake Chaohu, and the direction and speed of the prevailing wind determined the spatial distribution of these blooms. The cyanobacteria in Lake Chaohu were dominated by species of Microcystis and Anabaena. Microcystis reached its peak in June, and Anabaena had peaks in May and November, with an overall biomass that was higher than that of Microcystis. Microcystis generally occupied the western region of the lake in summer, whereas Anabaena dominated in other regions and seasons. Temperature may be responsible for these seasonal shifts. However, total phosphorus (TP), pH, temperature, turbidity and nitrate/nitrite nitrogen determined the coexistence of the two genera in different regions in summer. TP was correlated with Microcystis dominance, and pH and light availability were correlated with Anabaena dominance. Our results contribute to the understanding of shifts in bloom‐forming cyanobacteria and are important for the control of cyanobacterial blooms.     

Role of Predatory Bacteria in the Termination of a Cyanobacterial Bloom

Changes in cyanobacterial abundance and in the occurrence of bacteria of bacteria capable of lysing cyanobacteria were monitored over a period of 6 months (May to October 1998) in eutrophic Brome Lake (Quebec, Canada), in which dense cyanobacterial blooms recur regularly. By screening lake water, we isolated two strains of lytic bacteria, from the family Cytophagaceae. When tested on 12 cyanobacteria and 6 heterotrophic bacteria, strain 1 lysed only Anabaena flos-aquae and strain 2 lysed only Synechococcus cedorum, Synechococcus leopoliensis, Synechococcus elongatus, and Anacystic nidulans: both liquid and agar-grown cultures of these cyanobacteria were lysed. The number of plaque forming units of bacteria increased dramatically during the decline of the bloom. The results are consistent with an important role for these host-specific lytic bacteria in control and elimination of cyanobacterial blooms in this lake.     

Targeted deep sequencing reveals high diversity and variable dominance of bloom-forming cyanobacteria in eutrophic lakes

Cyanobacterial blooms in eutrophic lakes are severe environmental problems worldwide. To characterize the spatiotemporal heterogeneity of cyanobacterial blooms, a high-throughput method is necessary for the specific detection of cyanobacteria. In this study, the cyanobacterial composition of three eutrophic waters in China (Taihu Lake, Dongqian Lake, and Dongzhen Reservoir) was determined by pyrosequencing the cpcBA intergenic spacer (cpcBA-IGS) of cyanobacteria. A total of 2585 OTUs were obtained from the normalized cpcBA-IGS sequence dataset at a distance of 0.05. The 238 most abundant OTUs contained 92% of the total sequences and were classified into six cyanobacterial groups. The water samples of Taihu Lake were dominated by Microcystis, mixed Nostocales species, Synechococcus, and unclassified cyanobacteria. Besides, all the samples from Taihu Lake were clustered together in the dendrogram based on shared abundant OTUs. The cyanobacterial diversity in Dongqian Lake was dramatically decreased after sediment dredging and Synechococcus became exclusively dominant in this lake. The genus Synechococcus was also dominant in the surface water of Dongzhen Reservoir, while phylogenetically diverse cyanobacteria coexisted at a depth of 10 m in this reservoir. In summary, targeted deep sequencing based on cpcBA-IGS revealed a large diversity of bloom-forming cyanobacteria in eutrophic lakes and spatiotemporal changes in the composition of cyanobacterial communities. The genus Microcystis was the most abundant bloom-forming cyanobacteria in eutrophic lakes, while Synechococcus could be exclusively dominant under appropriate environmental conditions.     

Mesozooplankton and microzooplankton grazing during cyanobacterial blooms in the western basin of Lake Erie

Lake Erie is the most socioeconomically important and productive of the Laurentian (North American) Great Lakes. Since the mid-1990s cyanobacterial blooms dominated primarily by Microcystis have emerged to become annual, late summer events in the western basin of Lake Erie yet the effects of these blooms on food web dynamics and zooplankton grazing are unclear. From 2005 to 2007, grazing rates of cultured (Daphnia pulex) and natural assemblages of mesozooplankton and microzooplankton on five autotrophic populations were quantified during cyanobacterial blooms in western Lake Erie. While all groups of zooplankton grazed on all prey groups investigated, the grazing rates of natural and cultured mesozooplankton were inversely correlated with abundances of potentially toxic cyanobacteria (Microcystis, Anabaena, and Cylindrospermopsis; p < 0.05) while those of the in situ microzooplankton community were not. Microzooplankton grazed more rapidly and consistently on all groups of phytoplankton, including cyanobacteria, compared to both groups of mesozooplankton. Cyanobacteria displayed more rapid intrinsic cellular growth rates than other phytoplankton groups under enhanced nutrient concentrations suggesting that future nutrient loading to Lake Erie could exacerbate cyanobacterial blooms. In sum, while grazing rates of mesozooplankton are slowed by cyanobacterial blooms in the western basin of Lake Erie, microzooplankton are likely to play an important role in the top-down control of these blooms; this control could be weakened by any future increases in nutrient loads to Lake Erie.     

Cyanobacterial calcification, carbon dioxide concentrating mechanisms, and Proterozoic–Cambrian changes in atmospheric composition

Photosynthetic uptake of inorganic carbon can raise the pH adjacent to cyanobacterial cells, promoting CaCO₃ precipitation. This effect is enhanced by CO₂ concentrating mechanisms that actively transport into cells for carbon fixation. CO₂ concentrating mechanisms presumably developed in response to atmospheric decrease in CO₂ and increase in O₂ over geological timescales. In present‐day cyanobacteria, CO₂ concentrating mechanisms are induced when the atmospheric partial pressure of CO₂ (p_CO2) falls below ～0.4%. Reduction in p_CO2 during the Proterozoic may have had two successive effects on cyanobacterial calcification. First, fall in p_CO2 below ～1% (33 times present atmospheric level, PAL) resulted in lower dissolved inorganic carbon (DIC) concentrations that reduced pH buffering sufficiently for isolated CaCO₃ crystals to begin to nucleate adjacent to cyanobacterial cells. As a result, blooms of planktic cyanobacteria induced precipitated ‘whitings’ of carbonate mud in the water column whose sedimentary accumulation began to dominate carbonate platforms ～1400–1300 Ma. Second, fall in p_CO2 below ～0.4% (10 PAL) induced CO₂‐concentrating mechanisms that further increased pH rise adjacent to cells and promoted in vivo cyanobacterial sheath calcification. Crossing of this second threshold is indicated in the fossil record by the appearance of Girvanella 750–700 Ma. Coeval acquisition of CO₂ concentrating mechanisms by planktic cyanobacteria further stimulated whiting production. These inferences, that p_CO2 fell below ～1%～1400–1300 Ma and below ～0.4% 750–700 Ma, are consistent with empirical and modelled palaeo‐atmosphere estimates. Development of CO₂ concentrating mechanisms was probably temporarily slowed by global cooling ～700–570 Ma that favoured diffusive entry of CO₂ into cells. Lower levels of temperature and DIC at this time would have reduced seawater carbonate saturation state, also hindering cyanobacterial calcification. It is suggested that as Earth emerged from ‘Snowball’ glaciations in the late Neoproterozoic, global warming and O₂ rise reactivated the development of CO₂ concentrating mechanisms. At the same time, rising levels of temperature, calcium ions and DIC increased seawater carbonate saturation state, stimulating widespread cyanobacterial in vivo sheath calcification in the Early Cambrian. This biocalcification event promoted rapid widespread development of calcified cyanobacterial reefs and transformed benthic microbial carbonate fabrics.     

Structuring of the cyanobacterial community by pelagic fish in subtropical reservoirs: experimental evidence from Australia

1. Subtropical reservoirs of Australia are commonly subject to summer blooms of cyanobacteria. The potential for food web manipulation to control cyanobacterial blooms was investigated in Lake Maroon, south east Queensland using enclosures in which the density of the Australian gudgeon Hypseleotris spp. was manipulated. 2. Zooplankton biomass and community structure were strongly affected by fish density. A size dependent predation effect of Hypseleotris on zooplankton was observed at ambient fish densities, and the community shifted towards a dominance of copepod juveniles and nauplii. Substantial increases in the populations of Ceriodaphnia and calanoid copepods were observed at low fish densities and in the absence of fish. 3. At ambient fish densities total phytoplankton and the proportion of cyanobacteria were maintained at levels similar to those prevailing at day 0. Total phytoplankton and the proportion of cyanobacteria decreased substantially at low fish densities and in the absence of fish. Chlorophytes became dominant in the ‘no fish’ treatment and the grazing‐resistant species Oocystis and Dictyosphaerium were significantly higher than at ambient fish densities. 4. The experiment demonstrated a strong positive relationship between Hypseleotris density and cyanobacteria, and the results suggest that subtropical reservoirs may be suited to food web manipulation as a means of controlling summer cyanobacterial blooms.     

A survey of toxicity of cyanobacterial blooms in Lake Ladoga and adjacent water bodies

Twentyfive cyanobacterial blooms in Lake Ladoga and adjacent water bodies were studied in the summer of 1990–1992. Toxicity of the water bloom material for mice was detected in 9 cases. The maximal tolerable doses (MTD) of the material extracted from biomass varied within 3–30 mg kg^–1 mouse body weight; 50% lethal doses (LD₅₀) were within 45–125 mg kg^–1. Toxic water blooms were registered in Karelian lakes and in the Neva Bay, Gulf of Finland. Cyanobacterial samples collected on the eastern coast of Lake Ladoga proved to be non-toxic. The species identified in toxic bloom material included Anabaena circinalis, A. flos-aquae, A. lemmermannii, Anabaena sp., Aphanizomenonflos-aquae, Gloeotrichia echinulata, G. pisum, Microcystis aeruginosa and Oscillatoria sp. These data suggest that toxic forms of cyanobacteria are widespread in Karelian lakes belonging to the drainage basin of Lake Ladoga.     

Hyperspectral remote sensing of cyanobacterial pigments as indicators of the iron nutritional status of cyanobacteria-dominant algal blooms in eutrophic lakes

Iron can stimulate cyanobacterial growth. Determining iron availability to cyanobacteria is therefore essential for timely warnings of bloom development. The objectives of this study were to determine the key spectral parameters indicating cellular iron status in cyanobacteria and to establish reliable equations for estimating iron nutrition in cyanobacterial cells. Cells, pigments, cellular iron, and spectra of cyanobacteria were measured monthly at 17 sites in Meiliang Bay of Taihu Lake during the summer period of cyanobacterial blooms from 2010 to 2013. Pronounced spatial and temporal variability of cellular iron of cyanobacteria was observed. The previously developed structure-insensitive pigment index (SIPI) and plant senescence reflectance index (PSRI) and the newly proposed chlorophyll a/phycocyanin index (R_Chl/PC) exhibited strong relationships with cyanobacterial cellular iron content. The relationships between the cellular iron concentration and SIPI, PSRI and R_Chl/PC could be expressed as linear, quadratic and cubic functions, respectively. The equations derived herein were tested using independent data from 2008 to 2009, obtained from 31 sites within Taihu Lake. For the three models that included SIPI, PSRI and R_Chl/PC as predictors, the coefficients of determination (R²) between the measured and estimated cellular iron concentration were 0.549, 0.584 and 0.909, and the mean relative errors (RE) were 17.1%, 18.1% and 8.0%, respectively. The overall results indicated that use of the three key hyperspectral parameters, SIPI, PSRI and R_Chl/PC, could be used for non-destructive and real-time monitoring of the iron nutritional status of cyanobacteria-dominant algal blooms in eutrophic lakes.     

Understanding cyanobacteria‐zooplankton interactions in a more eutrophic world

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Nitrification and denitrification by algae-attached and free-living microorganisms during a cyanobacterial bloom in Lake Taihu,a shallow Eutrophic Lake in China

Cyanobacterial blooms may stimulate epiphytic nitrification and denitrification in the water column. To validate this hypothesis, a 4-week floating mesocosms experiment that involved a cyanobacterial decay–growth–decay period was conducted at Lake Taihu. In addition to conventional methods for detecting the physical and chemical properties, quantitative real-time PCR was used to identify the nitrification and denitrification genes (archaeal and bacterial amoA, nirS and nirK). Treatment with cyanobacteria led to removal of about 3.62 mg N L^?1 total nitrogen, 40% of which was organic nitrogen, indicating a nitrogen transformation and removal mechanism was present in the system. Variations in the biogeochemical properties suggested that remineralization and coupling nitrification and denitrification by epiphytic and pelagic microorganisms was the primary pathway through which organic nitrogen was removed. The results of this study revealed that algal blooms can accelerate nitrogen removal efficiency, which may be the primary reason that nitrogen is limited in summer in Lake Taihu.     

洱海蓝藻爆发的时空特征及影响因子

湖泊生态环境对区域气候变化和流域人类活动十分敏感。随着流域的持续开发,洱海作为云贵高原第二大淡水湖泊面临着严重的生态与环境问题,主要包括水质恶化和生态功能的衰退,其中蓝藻水华问题尤为突出。针对湖泊现代监测数据存在时间序列较短、连续监测记录缺乏、监测位点不完全一致等问题,应用沉积物记录开展色素等多指标分析和环境变化重建研究,并对洱海湖区南、中、北3个湖盆的沉积物记录进行对比分析,从而探讨洱海富营养化与蓝藻爆发的历史与变化特征,并识别藻类响应模式的空间异同。沉积物色素记录结果表明,洱海蓝藻生物量变化具有明显的时空差异性,呈现由南至北,先后增加、最后呈现蓝藻水华全湖性持续爆发的模式。进一步的简约模型方差分解结果表明气候变暖和营养盐富集是洱海蓝藻生物量变化的主要驱动因子,此外相对较浅的南部湖盆还受到水位波动、水动力减弱、水生植物演化的综合影响。因此,在气候变暖的背景下,控制水体营养盐输入、合理调控湖泊水位、提高水体透明度并恢复水生植物是控制洱海蓝藻水华爆发和进行生态恢复的重要措施。     

Diversity and dynamics of microcystin—Producing cyanobacteria in China's third largest lake, Lake Taihu

Microcystins (MC), the most prevalent group of harmful cyanobacterial hepatotoxins, are primarily produced by strains of cyanobacteria in Microcystis, Anabaena and Planktothrix. Lake Taihu, which is the third largest freshwater lake in China, is a hypertrophic shallow lake in eastern China that has experienced lake-wide cyanobacterial blooms annually during the last few decades. In this study, PCR-DGGE was used to evaluate the diversity of potential MC-producing cyanobacteria and real-time PCR was used to analyze the dynamics of this population based on the presence of the mcy gene in samples collected during a year long study. The results revealed that all MC-producing genotypes detected belonged to the genus Microcystis. In addition, the MC-producing genotype communities were more diverse during the bloom season than the non-bloom season, and the diversity in the late bloom period was lower than the diversity in the early bloom period. Furthermore, the abundance of MC-producing genotypes increased dramatically during the bloom development period, reaching its peak in late summer (September). The results also suggested that the highest mcy gene concentration lagged behind the highest MC concentration, and the potential MC-producing cyanobacterial community shift lagged behind the development of blooms.     

Increasing dominance of small zooplankton with toxic cyanobacteria

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Cyanobacterial carotenoids: their roles in maintaining optimal photosynthetic production among aquatic bloom forming genera

Summary Photoprotective and photosynthetic roles of carotenoid pigments (xanthophylls and -carotene) were examined in the major bloom forming blue-green algal (cyanobacterial) genera, Anabaena, Aphanizomenon and Microcystis. Since these genera often reside as scums in surface waters, attention was given to the ability of carotenoids to counter potential photooxidation due to maximum near U.V. and visible radiation as well as O₂ supersaturation, characterizing surface waters supporting blooms. In U.V.-transparent quartz incubation flasks it was shown that inhibition of carotenoid synthesis by diphenylamine led to rapid photooxidation among the above genera. When carotenoid synthesis was allowed to proceed, a high degree of resistance to photooxidation resulted. Prolonged exposure to near U.V. irradiation led to enhanced carotenoid synthesis relative to chlorophyll a, which extended viability. Carotenoid enhancement also increased chlorophyll a-specific photosynthetic O₂ production. It is concluded that enhanced carotenoid synthesis observed during blooms serves at least two ecological functions, i) providing photoprotection and ii) increasing photosynthetic performance of surface cyanobacterial populations.     

Cyanobacterial dynamics in shallow Lake Apopka (Florida,U.S.A.) before and after the shift from a macrophyte‐dominated to a phytoplankton‐dominated state

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Effects of light and temperature on the odor production of 2-methylisoborneol-producing Pseudanabaena sp. and geosmin-producing Anabaena ucrainica (cyanobacteria)

Frequent off-flavor events caused by geosmin and 2-methylisoborneol (MIB) have attracted research on the main producers, cyanobacteria. This study evaluated the effects of light and temperature on the odor production of MIB-producing Pseudanabaena sp. Lauterborn and geosmin-producing Anabaena ucrainica (Schhorb.) Watanabe. The maximum MIB production and lowest growth rate (indicated by the chlorophyll a (Chl a)) were observed at 35 °C compared with that at 10 °C and 25 °C. Cultures grown under a light intensity of 60 μmol photons m⁻² s⁻¹ demonstrated the highest MIB production and minimum growth rate, whereas the minimum MIB production and maximum growth rate were obtained under 10 μmol photons m⁻² s⁻¹. Similar patterns were observed for geosmin production. A. ucrainica had the highest geosmin production and lowest Chl a concentration under 10 °C and 60 μmol photons m⁻² s⁻¹. Moreover, greater proportions of geosmin and MIB were released into extracellular under growth-inhibiting temperatures and light intensities. An inverse correlation between odor production and the cell growth rate was suggested, and this relationship may reflect the competition for substrates of odor and Chl a synthesis. Thus, the accumulation of geosmin and MIB was probably the result of decreased cellular metabolic activity in cyanobacteria.     

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.