Current Trend of Metagenomic Data Analytics for Cyanobacteria Blooms

Cyanobacterial harmful algal blooms are a major threat to freshwater eco-systems globally. To deal with this threat, researches into the cyanobacteria bloom in fresh water lakes and rivers have been carried out all over the world. This review presents an overlook of studies on cyanobacteria blooms. Conventional studies mainly focus on investigating the environmental factors influencing the blooms, with their limitation in lack of viewing the microbial community structures. Metagenomics study provides insight into the internal community structure of the cyanobacteria at the blooming, and there are researchers reported that sequence data was a better predictor than environmental factors. This further manifests the significance of the metagenomic study. However, large number of the latter appears to be confined only to present snapshoot of the microbial community diversity and structure. This type of investigation has been valuable and important, whilst an effort to integrate and coordinate the conventional approaches that largely focus on the environmental factors control, and the Metagenomics approaches that reveals the microbial community structure and diversity, implemented through machine learning techniques, for a holistic and more comprehensive insight into the cause and control of Cyanobacteria blooms, appear to be a trend and challenge of the study of this field.

Monitoring cyanobacteria-dominant algal blooms in eutrophicated Taihu Lake in China with synthetic aperture radar images

Monitoring algal blooms by optical remote sensing is limited by cloud cover.In this study,synthetic aperture radar(SAR) was deployed with the aim of monitoring cyanobacteria-dominant algal blooms in Taihu Lake in cloudy weather.The study shows that dark regions in the SAR images caused by cyanobacterial blooms damped the microwave backscatter of the lake surface and were consistent with the regions of algal blooms in quasi-synchronous optical images,confirming the applicability of SAR for detection of surface blooms.Low backscatter may also be associated with other factors such as low wind speeds,resulting in interference when monitoring algal blooms using SAR data alone.After feature extraction and selection,the dark regions were classified by the support vector machine method with an overall accuracy of 67.74%.SAR can provide a reference point for monitoring cyanobacterial blooms in the lake,particularly when weather is not suitable for optical remote sensing.Multi-polarization and multi-band SAR can be considered for use in the future to obtain more accurate information regarding algal blooms from SAR data.

Community Structures of Phytoplankton with Emphasis on Toxic Cyanobacteria in an Ohio Inland Lake during Bloom Season

The community structures of phytoplankton are important factors and indicators of lake water quality. Harmful algal blooms severely impact water supply, recreational activities and wildlife habitat. This study aimed to examine the phytoplankton composition and variations using microscopy, and identify harmful Cyanobacteria in weekly samples taken from four sites at Harsha Lake in southwest Ohio. Over the course of the summer in 2015, the phytoplankton of Harsha Lake consisted mainly of 13 taxa belonging to Bacillariophyta, Chlorophyta, Cryptophyta, Cyanobacteria, Dinophyta and Euglenophyta. Their significant successions started with Bacillariophyta and/or Chlorophyta, then bloomed with Cyanobacteria and ended with Chlorophyta and/or Dinophyta. Cyanobacteria members: Microcystis, Planktothrix, Dolichospermum, Aphanizomenon, Cylindrospermopsis, and Oscillatoria from the Cyanophyceae were identified to be dominant genera. These organisms varied spatially and temporally in similar patterns along with the variations of nutrients and formed the summer bloom with the total biomasses ranging from 0.01 to 114.89 mg L-1 with mean of 22.88 mg L-1. M. aeruginosa and P. rubescens were revealed as the microcystin producers, while A. circinalis and Aphanizomenon sp. were identified as a saxitoxin producer through cloning and sequencing PCR products of mcyA, mcyE and sxtA genes. The biomasses of phytoplankton, Cyanobacteria and Microcystis were positively correlated to nutrients, especially to total nitrogen. The total ELISA measurement for microcystin positively correlated with Cyanobacteria (R2 = 0.66, P Microcystis (R2 = 0.64, P 2 = 0.59, P < 0.0001). The basic information on the occurrence and biomasses of Cyanobacteria and total phytoplankton, and the analysis for toxic species, which were the first report for the inland water in Ohio, USA, will document the succession patterns of phytoplankton and toxin production over a season and provide data to predict risk occurrence to both human and ecological factors.

Variation of phytoplankton community before an induced cyanobacterial(Arthrospira platensis) bloom

A cyanobacterial （Arthrospira platensis） bloom was induced in situ by nutrient manipulation in an enclosure. The succession of the phytoplankton community and the water chemistry variations before the appearance of bloom, as well as their relationship, were investigated. The cell pigment variations were studied simultaneously. The Pearson＇s correlation analysis showed that there was no significant correlation between water chemistry and green algal or cyanobacterial composition, indicating that water chemistry variations were not suitable to be used as indicators for cyanobacterial-bloom early-warning. However, the diversity index of the phytoplankton community decreased sharply before the bloom appeared. Therefore, the dynamics of phytoplankton community was put forward to be an indicator for cyanobacterial-bloom early-warning. In addition, the cell pigment variations represented the changes of community structure, which should be useful for studying the dynamics of phytoplankton community.

Classification of Toxic Cyanobacterial Blooms by Fourier-Transform Infrared Technology (FTIR)

Cyanobacteria are gram-negative photosynthetic bacteria capable of producing toxins responsible for morbidity and mortality in humans and domestic animals. They are capable of forming concentrated blooms, referred to as harmful algal blooms (HABs). Characterization of HABs is necessary to reduce risks from human and animal exposures to toxins. Current methods used to classify cyanobacteria and cyanotoxins have limitations related to time, analyst skills, and cost. Fourier-Transform Infrared Spectroscopy (FTIR) is a potential tool for rapid, robust cyanobacterial classification that is not limited by these factors. To examine the practicality of this method, library screening with default software algorithms was performed on HAB samples, followed by principle component cluster analyses and dendrogram analysis of samples meeting minimum quality requirements. Two tested spectrometers and software packages were successful at distinguishing cyanobacteria from green algae. Principle component cluster analysis and dendrogram analysis also resulted in clear differentiation between cyanobacteria and green algae. While these methods cannot be used independently to fully characterize HABs, they show the potential and practicality of FTIR as a screening tool.

Molecular and Chemical Analyses of Cyanobacterial Blooms in Tropical Lagoons from Southeast Brazil

The genetic diversity and the potential toxicity of bloom-forming cyanobacteria were studied in four lagoons located in the state of Sao Paulo (Campinas, Limeira and Piracicaba cities). Bloom samples were collected on the water surface and cyanobacterial communities were evaluated using DGGE fingerprinting and 16S rDNA clone library. The amplification of genes encoding secondary metabolites such as microcystin (mcy), anatoxin (ana), cylindrospermopsin (cyr), saxitoxin (sxt), cyanopeptolin (mcn) and aeruginosin (aer) was performed and their production analyzed by LC-MS. The comparison of DGGE banding pattern among the different water samples suggested that some operational taxonomic units (OTUs) in these locations were predominant over others. The 16S rDNA clone libraries sequences matched with nine different known cyanobacterial genera available in NCBI, identified as Anabaena, Brasilonema, Cylindrospermopsis, Limnococcus, Microcystis, Nostoc, Pseudanabaena, Synechococcus and Woronichinia. The lagoons ESALQ2, Taquaral and Limeira had more than 80% of the cyanobacterial community assigned to the genus Microcystis. Genes encoding aeruginosin, cyanopeptolin and microcystin synthetases and saxitoxin synthase were amplified, and LC-MS/MS confirmed the production of aeruginosin, cyanopeptolin and microcystin. Rapid and sensitive methods for the detection of these secondary metabolites, especially toxins, using chemical and molecular tools together, can be used for a faster diagnostic of toxic cyanobacterial blooms.

Cyanobacteria Diversity in Blooms from the Greater Sudbury Area

The Greater Sudbury Area is approximately 400 km north of the city of Toronto and falls within a large number of temperate lakes of various sizes. This area has been mined for nickel and other metals for several decades. These activities have affected the watersheds of Northern Ontario and have influenced the chemistry of a number of lakes. Blooms of cyanobacteria occur yearly in several lakes, mainly in the early and late summer months. Much of the chemistry of these lakes is known but the nature of the cyanobacterial blooms and the factors that may contribute to their sudden appearance are not. We sampled blooms from five Greater Sudbury Area lakes and identified the species present by morphological and molecular methods. The dominant genera present as characterized by morphological examination were Synechocystis, Leptolyngbya, Anabaena, Cyl-indrospermum, Nostoc, Borzia, Phormidium, Pseudoanabaena, Oscillatoria, and Planktothrix. Three of these isolates, Leptolyngbya, Anabaena, and Planktothrix were confirmed by partial rRNA sequence analysis.

束丝藻的竞争优势及其驱动机制的研究进展

束丝藻(Aphanizomenon)是一种丝状固氮蓝藻,具有入侵性且易暴发有害水华。近年来,在全球气候变化推动下束丝藻的扩张已然成为一种世界范围的现象,其广泛分布在温带、热带水体中,因其能合成藻毒素和异味物质而严重影响水生态系统功能,威胁饮用水安全和人类健康。束丝藻耐低温、喜低光,在偏碱性、低氮高磷水体中增殖较快,并凭其固氮、储磷以及释放藻毒素、形成群体胶鞘等独特生态策略使其在种间竞争以及群落结构演替中获得较大竞争优势,成为优势种群。鉴于束丝藻的危害性和扩张性,本文从束丝藻的生理生态特性、分布特征、竞争优势及其关键驱动因子等研究前沿进行了综述,并对相关研究领域进行展望,为进一步研究束丝藻种群竞争优势形成机制,有效防控束丝藻水华提供科学依据。

淡水硅藻水华成因与控制技术研究进展

在全球气候变暖和人类活动的共同影响下,硅藻水华爆发趋势加剧,并对水生态及供水安全产生负面影响.因此明确其形成原因并探索高效的防控技术至关重要.目前关于淡水硅藻水华已有较多研究成果,但缺少系统性整理.淡水硅藻水华爆发的关键因素为温度、光照、营养盐和流速.在原位防控方面,生态调度和扬水曝气等物理技术较为成熟,低剂量的化学药剂处理效果不佳,而生物方法的实施会受到环境条件的限制.联合使用混凝剂和助凝剂或氧化剂可以有效去除硅藻,但硅藻水华范围的扩大致使部分水厂未能及时调整工艺,影响制水效率.本文对硅藻水华的成因及防治方法进行了分析和总结,与蓝藻水华进行比较,并展望后续研究热点,对确保饮用水安全和水体污染控制与治理有着重要意义.

环境微生物对水体中微囊藻毒素降解机制的研究进展

近年来,全球气候变暖和水体富营养化加剧导致蓝藻水华污染严重,而大部分蓝藻水华暴发后产生的微囊藻毒素(Microcystins,MCs)极具危害性,对人类健康和水生生态系统构成威胁。有效控制和去除水体中的MCs已成为当前亟需解决的一项难题。现有研究表明,微生物降解MCs具有高效和环保的治理效益。因此,本文综述了MCs的产生、结构和毒性危害,并着重介绍了国内外学者在微生物降解MCs的酶促降解途径、降解基因和降解酶领域的研究进展;此外,还分析了微生物降解菌在水体生态修复中的潜在应用,并展望了对MCs的非mlr降解途径机制、优化表达MCs降解酶、构建高效双功能降解菌等未来研究方向,旨在为深入研究MCs微生物降解机制并有效改善全球水体中MCs污染现状提供新思路。

微囊藻毒素的检测和脱除方法研究进展

近年来,由于富营养化,全球有害蓝藻水华的发生率持续上升,形成水华的蓝藻会释放出多种毒素。微囊藻毒素是有害蓝藻产生的常见毒素,具有肝毒性、肾毒性、神经毒性、生殖毒性等多种毒性,严重威胁人类和生态系统健康。微囊藻毒素在水中非常稳定,难以通过传统水处理工艺去除。因此,寻求经济有效的微囊藻毒素检测和脱除方法至关重要。本文综述了定量检测和去除微囊藻毒素的方法,包括物理法、化学法和生物法,并分析总结了这3类方法用于检测和脱除微囊藻毒素的优势与局限性,总结了不同方法脱除微囊藻毒素的机理,重点介绍了绿色高效的光催化与安全有效的生物方法脱除微囊藻毒素,最后基于当前的研究结果,对未来微囊藻毒素脱除研究方向进行了展望,为解决环境中微囊藻毒素的污染问题提供思路。

风场对鄱阳湖丰水期表层蓝藻密度的影响

目前,在风场对蓝藻的影响研究方面,国内针对太湖、滇池、巢湖等浅水湖泊的研究较多,针对鄱阳湖的研究则多集中于蓝藻群落特征及其与营养盐之间的关系。近年来,作为长江流域重要的通江湖泊,处于轻度富营养化状态的鄱阳湖水体蓝藻水华在局部库湾和部分水域出现,风场如何影响鄱阳湖表层蓝藻密度是一个值得探讨的问题。20192021年,在鄱阳湖布设13~49个采样点,于平水期、丰水期和枯水期现场采集各个点位表层水样、藻类、风场和流场数据,分析风场对鄱阳湖丰水期表层蓝藻密度的影响。结果表明,20192021年鄱阳湖丰水期风速与表层蓝藻密度呈显著正相关性,风场对水体的充分混合及驱动水体形成的风生流是促进蓝藻生长的原因之一。在流速较高(>0.05 m/s)的区域,无论风速高于还是低于临界风速(3~4 m/s),鄱阳湖表层蓝藻密度的空间分布受流场的影响更大;在流速较低(<0.05 m/s)的区域,风速在临界风速以下时,鄱阳湖表层蓝藻密度的空间分布受风场影响更大。20192021年鄱阳湖丰水期蓝藻密度超过水华暴发的阈值,但在高风速高流速的共同作用下未能发生大范围的蓝藻水华,仅能在风速适宜(<3~4 m/s)、流速较低(<0.05 m/s)的内湾、尾闾区等区域发生小面积的蓝藻水华。鄱阳湖丰水期水体处于长江顶托的低流速且微风条件下时,发生大面积蓝藻水华的概率可能会明显上升。

基于遥感影像的多方法评估氮元素对太湖水华影响

氮元素与太湖水华暴发有强相关性,是太湖水华暴发的重要因子.论文基于多源数据深入探讨了氮元素对太湖蓝藻水华暴发的影响机制.结果显示,氮元素通过营养盐释放和循环利用推动水华暴发,与蓝藻生长之间构成正反馈.高水温下,蓝藻生长与反硝化过程对硝态氮的竞争,削弱了反硝化微生物的脱氮效果,导致太湖水华持续化.相关性分析表明,不同形态氮与叶绿素a之间存在显著相关.论文从多层次、多角度解析氮元素与太湖水华暴发的关联机制,研究结果可为水体生态修复和水环境管理决策提供科学依据.

Cyanobacteria Growth in Nitrogen- &Phosphorus-Spiked Water from a Hypereutrophic Reservoir in Kentucky, USA

Cyanobacteria may adversely impact aquatic ecosystems through oxygen depletion and cyanotoxin production. These cyanotoxins can also harm human health and livestock. In recent years, cyanobacterial blooms have been observed in several drinking water reservoirs in Kentucky, United States. In Kentucky, the paradigm is that phosphorous is the limiting nutrient for cyanobacteria growth. To explore this paradigm, an indoor microcosm study was conducted using hypereutrophic Guist Creek Lake water. Samples were collected and spiked with various combinations of locally used agricultural grade fertilizers, including ammonium nitrate, urea, and triple phosphate (calcium dihydrogen phosphate). Samples were incubated indoors for the photoperiod-specific to the time of the year. Cyanobacteria density, measured by phycocyanin, did not demonstrate increased growth with the addition of phosphate fertilizer alone. Cyanobacteria growth was enhanced in these conditions by the combined addition of ammonium nitrate, urea, and phosphorus fertilizer. Growth also occurred when using either ammonium nitrate or urea fertilizer with no additional phosphorus input, suggesting that phosphorus was not limiting the cyanobacteria at the time of sample collection. The addition of both nitrogen fertilizers (ammonium nitrate and urea) at the concentrations used in this study, in the absence of phosphorus, was deleterious to both the Chlorophyta and cyanobacteria. The results suggest further studies using more robust experimental designs are needed to explore lake-specific dual nutrient management strategies for preventing cyanobacterial blooms in this phosphorus-rich hypereutrophic lake and possibly other hypereutrophic lakes.

The trophic state of lake water regulates spatial-temporal variations of bloom-forming Microcystis

Although biomass variations in Microcystis and microcystin have been widely reported,few studies have addressed whether different trophic states of natural lake water affect the spatial-temporal variations in abundances of microcystin-producing Microcystis in a given bloom.In this study,we used a harmful algal bloom in Chaohu Lake,eastern China,as an example to investigate the mutual relationship between different nutrient states and environmental factors,and the impact on Microcystis.Overall,cyanobacteria and Microcystis were more abundant in the middle and western parts of the lake under high nutrients levels,while in the eastern part,nutrient concentrations were low enough to limit biomass,and their fluctuations affected the contents of toxic Microcystis.Moreover,microcystin concentration was correlated positively to nutrient levels and Microcystis biomass during bloom developing in 2013 from June to August.Temporally,the cellular content of total microcystin was lowest when the bloom peaked in intensity.Our results suggest that lake eutrophication not only results in cyanobacterial blooms,but may also increase the proportion of toxic Microcystis species and their cell-bound MCs contents(i.e.microcystin cell quotas) under mild eutrophication.The present investigation provided molecular evidence for the selection of MC-producing and non-MC-producing genotypes.The current study provides new evidence advocating the monitoring of partitions of large lakes when studying cyanobacteria and toxin-contaminated freshwaters,which will be beneficial for both water agencies and water researchers.

Interactive Effects of Temperature, Nitrogen, and Zooplankton on Growth and Protein and Carbohydrate Content of Cyanobacteria from Western Lake Erie

Harmful algal blooms (HABs) in freshwater ecosystems, especially of cyanobacterial species, are becoming more frequent and expanding geographically, including in Lake Erie in North America. HABs are the result of complex and synergistic environmental factors, though N or P eutrophication is a leading cause. With global mean temperatures expected to increase an additional 2°C - 5°C by 2100, cyanobacterial blooms are predicted to increase even more, given their typically-high temperature optimum for growth. We investigated how increases in temperature and nitrogen, singly or in combination, affect the growth, food quality, and herbivory of Lake Erie cyanobacteria. Algal community samples collected from Lake Erie, and isolated non-N-fixing (Microcystis aeruginosa) and N-fixing (Anabaena flos-aquae) cyanobacterial species, were cultured at 20°C, 25°C, or 30°C, and at 5, 50, 150, or 250 μM N, and then analyzed for growth and (for isolates) content of total protein and non-structural carbohydrates (NSC). Temperature and N both affected algal growth, and there were temperature × N interactions, which were sometimes affected by presence/absence of zooplankton. For example, cyanobacteria (but not green algae) growth increased with both temperature and N, especially from 25°C to 30°C, but N and herbivore presence increased cyanobacterial growth primarily only at 30°C. In general, temperature and N had little consistent effect on NSC, but increasing temperature and N tended to increase protein content in Microcystis and Anabaena (temperature effects mostly at higher N levels). In Anabaena, increases in N did not increase growth or protein at 20°C or 25°C, but did increase both at 30°C, indicating that N fixation is damaged at high temperatures and that high NO3 can overcome this damage. These results indicate that future global warming and continued eutrophication will increase cyanobacterial growth, as well influence algal herbivory and competition between N-fixing and non-N-fixing cyanobacteria.

Hyperspectral Reflectance Characteristics of Cyanobacteria

Potentially harmful cyanobacterial blooms are an emerging environmental concern in freshwater bodies worldwide. Cyanobacterial blooms are generally caused by high nutrient inputs and warm, still waters and have been appearing with increasing frequency in water bodies used for drinking water supply and recreation, a problem which will likely worsen with a warming climate. Cyanobacterial blooms are composed of genera with known biological pigments and can be distinguished and analyzed via hyperspectral image collection technology such as remote sensing by satellites, airplanes, and drones. Here, we utilize hyperspectral microscopy and imaging spectroscopy to characterize and differentiate several important bloom-forming cyanobacteria genera obtained in the field during active research programs conducted by US Geological Survey and from commercial sources. Many of the cyanobacteria genera showed differences in their spectra that may be used to identify and predict their occurrence, including peaks and valleys in spectral reflectance. Because certain cyanobacteria, such as Cylindrospermum or Dolichospermum, are more prone to produce cyanotoxins than others, the ability to differentiate these species may help target high priority waterbodies for sampling. These spectra may also be used to prioritize restoration and research efforts to control cyanobacterial harmful algal blooms (CyanoHABs) and improve water quality for aquatic life and humans alike.

Role of Suspended Sediments and Mixing in Reducing Photoinhibition in the Bloom-Forming Cyanobacterium Microcystis

Toxic cyanobacterial blooms are becoming a global problem. Previous research of cyanobacterial bloom development has examined how high nutrient concentrations promote cyanobacteria dominance, and how positive buoyancy provides an ecological advantage over sinking phytoplankton. Tributaries responsible for loading nutrients into lakes often simultaneously contribute high concentrations of suspended sediments. High concentrations of suspended sediments may also influence blooms by affecting the ambient light climate, reducing photodamage, and increasing the efficiency of photosynthesis. We examined the effects of sediments and vertical mixing in potentially reducing photodamage to Microcystis by measuring photosynthetic parameters and pigment content of Microcystis in western Lake Erie during the 2008 bloom and in laboratory experiments. Photosynthetic efficiency increased with increasing sediment concentration in the lake and laboratory experiment. Content of photo-protective carotenoid pigments per dry weight decreased with increasing sediment concentrations, while the light-harvesting pigments, chl a and phycocyanin, increased with sediments. These results indicate that suspended sediments reduce photoinhibition for Microcystis. Further, photosynthetic damage was higher when Microcystis was concentrated on the surface compared to a mixed water column. Measurements of Microcystis abundance and light were also recorded, in addition to photosynthetic measurements. Greatest Microcystis abundances in Lake Erie were recorded during light-limiting conditions, which offer Microcystis both physiological and ecological benefits by reducing photoinhibition and increasing Microcystis’ advantage in light competition via buoyancy. Efforts to reduce cyanobacterial blooms may include reducing suspended sediments loads in combination with reducing nutrient loading.

江门市大中型水库水质状态及蓝藻水华风险评估

文章选取13宗大中型水库,根据2021年水生态监测和调查成果,并结合历史情况,分析水库水质和营养状态,并进行蓝藻水华风险评估。结果显示,汛期6宗水库水质优于或达到Ⅱ类,非汛期7宗水库水质优于或达到Ⅱ类。2021年7宗水库的营养状态为中营养,6宗水库营养状态为轻度富营养。2021年藻类总丰度超过水华发生限值(1×10^(7) ind/L)的水库有6宗。2010—2021年,发生过蓝藻水华的水库有9宗,尚未发生过蓝藻水华的水库有4宗。综合分析,2宗水库藻类水华发生风险等级为低,2宗水库水华发生风险等级为中,9宗水库藻类水华发生风险等级为高。

基于高频高光谱近感观测量化风对蓝藻水华的影响

全球气候变化显著影响湖泊理化环境和生态系统演化,对生态系统服务造成负面影响甚至引发生态系统灾变,其中风速下降可能促使富营养化湖泊蓝藻水华的暴发和水面漂浮集聚。以往由于较低的观测频次,往往很难精细量化风对蓝藻水华的影响。利用陆基高光谱近感观测技术,基于分钟小时尺度开展周年高频观测,通过对6—10月蓝藻生长期太湖表层水体叶绿素a浓度统计分析,量化蓝藻水华高频动态变化特征,确定蓝藻水华漂浮集聚的风速阈值。研究发现,随着风速的下降,水体表层叶绿素a浓度随之增加,蓝藻水华出现概率也随之增加。概率分析显示,当近地面风速小于2.5 m/s时,湖泊表层比较容易形成明显肉眼可见的蓝藻水华,藻华发生概率为55.1%。长时间持续的低风速容易诱发蓝藻水华形成和漂浮集聚,强风浪事件后低风速出现1~2天叶绿素a往往就能恢复以往较高水平,这为管理者有效防控蓝藻水华提供了新视角。长期气象观测显示,气候变化影响下太湖地区风速呈现显著下降趋势,增加了蓝藻竞争优势和发生概率,有助于其在表面漂浮集聚。在未来的气候变化情景下,如果风速继续呈现下降趋势,在营养盐条件不变情况下湖泊表层蓝藻水华发生概率可能还会上升,增加蓝藻水华防控难度,也对流域和湖体营养盐管控来缓解蓝藻水华提出更高要求。