Detection of toxigenicity by a probe for the microcystin synthetase A gene (mcyA) of the cyanobacterial genus Microcystis: comparison of toxicities with 16S rRNA and phycocyanin operon (Phycocyanin Intergenic Spacer) phylogenies

Harmful algal blooms in Cayuga lake, NY: From microbiome analysis to eDNA monitoring

The global increase in harmful algal blooms (HABs) has become a growing concern over the years, and New York State (NYS) is no exception. The Finger Lakes region in NYS has been identified as a hotspot for HABs, with Cayuga Lake having the highest number of blooms reported. The Cayuga Lake HABs Monitoring Program has been tracking cHABs (dominant bloom taxa, chlorophyll A, and microcystin levels) since 2018. However, limited research has been conducted on the microbiome of HABs in this region. In this study, the microbiome of HABs in the Cayuga Lake was surveyed and compared with non-HAB baseline samples. Using 16S rDNA community analysis, common bloom-forming cyanobacteria, were identified, with Microcystis being the dominant taxa in high toxin blooms. Further, this study evaluated the ability of Microcystis mcyA qPCR to detect elevated levels of potential toxigenic Microcystis in water samples using both benchtop and handheld qPCR devices. The results showed good performance of the qPCR assay as a screening for high toxin versus low/no toxin blooms. Additionally, the handheld qPCR device holds potential for in-field rapid (<1 h) screenings for high toxin blooms. This study provides insights into the microbiome of HABs in Cayuga Lake and offers a potential tool for rapid screening of high toxin blooms.

Changes in microcystin concentration in Lake Taihu, 13 years (2007-2020) after the 2007 drinking water crisis

Since the 2007 water crisis occurred in Lake Taihu, substantial measures have been taken to restore the lake. This study evaluates the effectiveness of these restoration activities. We examined the physicochemical parameters and the distribution of microcystin and Microcystis in both the water column and sediment during the bloom period of May 2020 to October 2020. The mean value of extracellular and intracellular microcystin content was 0.12 μg L-1 and 16.26 μg L-1, respectively. The mean value of microcystin in sediment was 172.02 ng g-1 and peaked in August. The concentration in the water and sediment was significantly lower than the historical average concentration. The abundance of toxigenic Microcystis and total Microcystis in the water column ranged from 2.61 × 102 to 2.25 × 109 copies·L-1 and 8.28 × 105 to 2.76 × 109 copies·L-1, respectively. The proportion of toxic Microcystis in the sediment ranging from 31.2% to 19.12%. The highest and lowest region was Meiliang Bay and Grass-algae type zone, respectively. The copy number of the 16S rRNA gene was 1-4 orders of magnitude higher than that of mcyA gene in populations of Microcystis, indicating that non-toxic Microcystis was the dominant form in the majority of the lake. The abundance of toxic Microcystis in the water column was positively correlated with total phosphorus, PO43--P and pH, while the water temperature played distinct role to the distribution of toxic Microcystis in sediment. Our research indicated phosphorus remains a key factor influencing the toxic Microcystis and microcystins in the water column. pH played distinct roles in the distribution of microcystins in sediment and water column. The increasing water temperature is a threat. Explicit management actions and policies, which take into account nutrient concentrations, pH, and increasing temperatures, are necessary to understand and control the distribution of microcystin and Microcystis in Lake Taihu.

Occurrence of Harmful Algal Blooms in Freshwater Sources of Mindu and Nyumba ya Mungu Dams, Tanzania

Harmful algal blooms (HABs) pose a significant threat to aquatic ecosystems and human health due to the production of toxins. The identification and quantification of these toxins are crucial for water quality management decisions. This study used DNA analysis (PCR techniques) to identify toxin-producing strains and liquid-chromatography-tandem mass spectrometry (LC-MS/MS) to quantify microcystins in samples from Mindu and Nyumba ya Mungu Dams in Tanzania. The results showed that HABs were detected in both dams. The BLAST results revealed that the 16S gene sequences of uncultured samples were very similar to an Antarctic cyanobacterium, Leptolyngbya sp, Anabaena sp, and Microcystis aeruginosa. Sequences of the cultured samples were most similar to Nodularia spumigena, Amazoninema brasiliense, Anabaena sp, and Microcystis aeruginosa. Further analyses showed that the nucleotide sequence similarity of uncultured isolates from this study and those from the GenBank ranged from 85 to 100%. For cultured isolates from this study and others from the GenBank, nucleotide identity ranged from 81 to 100%. The molecular identification of Microcystis aeruginosa confirmed the presence of HABs in both Mindu and Nyumba ya Mungu Dams in Tanzania. At Mindu Dam, the mean concentrations (± standard deviation) of microcystin-LR, -RR, and -YR were 1.08 ± 0.749 ppm, 0.120 ± 0.0211 ppm, and 1.37 ± 0.862 ppm, respectively. Similarly, at Nyumba ya Mungu Dam, the concentrations of microcystin-LR, -RR, and -YR were 1.07 ± 0.499 ppm, 0.124 ± 0.0224 ppm, and 0.961 ± 0.408 ppm, respectively. This paper represents the first application of PCR and LC-MS/MS to study microcystins in small freshwater reservoirs in Tanzania. This study confirms the presence of toxin-producing strains of Microcystis aeruginosa in both dams and also provides evidence of the occurrence of microcystins from these strains. These findings contribute in improving the monitoring of HABs contamination and their potential impact on water quality in Tanzanian reservoirs.

Cyanobacterial Algal Bloom Monitoring: Molecular Methods and Technologies for Freshwater Ecosystems

Cyanobacteria (blue-green algae) can accumulate to form harmful algal blooms (HABs) on the surface of freshwater ecosystems under eutrophic conditions. Extensive HAB events can threaten local wildlife, public health, and the utilization of recreational waters. For the detection/quantification of cyanobacteria and cyanotoxins, both the United States Environmental Protection Agency (USEPA) and Health Canada increasingly indicate that molecular methods can be useful. However, each molecular detection method has specific advantages and limitations for monitoring HABs in recreational water ecosystems. Rapidly developing modern technologies, including satellite imaging, biosensors, and machine learning/artificial intelligence, can be integrated with standard/conventional methods to overcome the limitations associated with traditional cyanobacterial detection methodology. We examine advances in cyanobacterial cell lysis methodology and conventional/modern molecular detection methods, including imaging techniques, polymerase chain reaction (PCR)/DNA sequencing, enzyme-linked immunosorbent assays (ELISA), mass spectrometry, remote sensing, and machine learning/AI-based prediction models. This review focuses specifically on methodologies likely to be employed for recreational water ecosystems, especially in the Great Lakes region of North America.

Morphological, molecular, and biochemical study of cyanobacteria from a eutrophic Algerian reservoir (Cheffia)

The cyanobacteria management in water bodies requires a deep knowledge of the community composition. Considering the reliable and thorough information provided by the polyphasic approach in cyanobacteria taxonomy, here we assess the cyanobacterial community structure of the Cheffia reservoir from Algeria. Cyanobacteria were identified on the basis of morphological traits and next-generation sequencing (NGS); toxins-related genes were localized in addition to the identification of toxins; temperature and nutrient level of water samples were also determined. The polyphasic approach was essential for cyanobacteria investigation; 28 genera were identified through 16S rRNA metabarcoding with the dominance of taxa from Microcystis (34.2%), Aphanizomenon (20.1%), and Planktothrix (20.0%), and morphological analysis revealed the association in this water body of five species within the genus Microcystis: M. aeruginosa, M. novacekii, M. panniformis, M. ichthyoblabe, and M. flos-aquae. The presence of mcyE genotypes was detected; moreover, HPLC-PDA and LC-ESI-MS/MS revealed the production of microcystin-LR. Results obtained in our study are very important since this ecosystem is used for water supply and irrigation; as a consequence, a good water management plan is essential.

Environmental factors associated with cyanobacterial assemblages in a mesotrophic subtropical plateau lake: A focus on bloom toxicity

Harmful algal blooms caused by cyanobacteria have been increasing in frequency worldwide. However, the main environmental drivers of this change are often difficult to identify because of the effects of the interaction between eutrophication and climate change. Recently, filamentous N₂-fixing cyanobacteria and non-diazotrophic Microcystis have been observed to be co-existing and undergoing succession in some eutrophic lakes. However, the succession patterns of dominant cyanobacteria and the factors driving this in mesotrophic lakes are not well understood. We hypothesized that the changes in cyanobacterial assemblages in mesotrophic lakes could result in a relatively high risks of toxic blooms, and that these changes are associated with the global climatic changes. We tested these hypotheses using data from the subtropical mesotrophic Lake Erhai. We found that the high spatiotemporal variability in the cyanobacterial community, and the increase in biomass were driven primarily by the growth of bloom-forming cyanobacterial taxa. Species-specific biomasses were related to a different environmental stressor; increases in dissolved organic carbon (DOC) concentrations were statistically associated with an increase of Microcystis biomass, whereas increases in surface water temperature favored higher biomass of Pseudanabaena at low transparency and high concentration of phosphorus. In addition, low nitrogen- to- phosphorus ratios were identified as potential determinants of the abundance of N₂-fixing Dolichospermum. Furthermore, changes in the concentration of DOC, total nitrogen, pH and water transparency levels were found to affect the composition of Microcystis morphotypes and genotypes mostly. This study highlights that the toxic to non-toxic Microcystis ratio might increase with the water darkening and browning (which occurs in many subtropical plateau lakes). Lake management strategies, therefore, need to consider the toxicity of cyanobacterial assemblages in mesotrophic lakes over the intensity of the cyanobacterial blooms.

Preliminary evidence on the presence of cyanobacteria and cyanotoxins from culture enrichments followed by PCR analysis: new perspectives from Africa (Mali) and South Pacific (Fiji) countries

Cyanobacteria are a group of microorganisms that can be found in a diverse range of biogeographical areas and produce potent and damaging cyanotoxins, which reveal importance for continuous studies and surveillance efforts. In this study, we analyzed worldwide two-month culture-enriched water samples collected from 12 distinct countries (Costa Rica, Cuba, Fiji, France, Indonesia, Mali, Portugal, South Africa, Spain, Thailand, USA, Vietnam) including two undisclosed areas (Fiji and Mali). We performed a PCR-based molecular multi-step scheme that consisted in the detection of the main cyanobacterial species, genera, and cyanotoxins biosynthesis genes. Results from this study indicate that Microcystis aeruginosa followed by Planktothrix agardhii were the most prevalent species of all the 12 countries analyzed. Cylindrospermospis raciborskii was detected in Costa Rica, while P. agardhii was detected in Fiji and South Africa. M. aeruginosa was detected in Fiji and Mali. Regarding the main cyanotoxins biosynthesis genes, a cyrC gene fragment (cylindrospermopsins) was amplified in the African continent (South Africa), while anaC (anatoxin-a) was detected in two distinct locations, Mali and Vietnam. Saxitoxins biosynthesis gene was also detected in Fiji and Vietnam. Microcystins biosynthesis gene (mcyA) was co-detected with anatoxin-a biosynthesis gene in Mali and with saxitoxins biosynthesis gene (sxtI) in Portugal. This study therefore constitutes a major contribution to the global biogeography of cyanobacteria and its cyanotoxins and recommends continuous vigilance of toxic cyanobacteria particularly in the more undisclosed areas of the world. The PCR analysis data obtained in our 2-month culture-enriched water samples supports molecular methods as a preliminary tool in the environmental surveillance of cyanobacteria and cyanotoxins in undisclosed locations, particularly since the several positive amplifications detected may indicate that though samples were collected under non-bloom conditions, if environmental conditions change in the ecosystem, there is a risk that bloom-forming species may arose along with their detected cyanotoxicity.

The genetic and ecophysiological diversity of Microcystis

Microcystis is a cyanobacterium that forms toxic blooms in freshwater ecosystems around the world. Biological variation among taxa within the genus is apparent through genetic and phenotypic differences between strains and via the spatial and temporal distribution of strains in the environment, and this fine-scale diversity exerts strong influence over bloom toxicity. Yet we do not know how varying traits of Microcystis strains govern their environmental distribution, the tradeoffs and links between these traits, or how they are encoded at the genomic level. Here we synthesize current knowledge on the importance of diversity within Microcystis and on the genes and traits that likely underpin ecological differentiation of taxa. We briefly review spatial and environmental patterns of Microcystis diversity in the field and genetic evidence for cohesive groups within Microcystis. We then compile data on strain-level diversity regarding growth responses to environmental conditions and explore evidence for variation of community interactions across Microcystis strains. Potential links and tradeoffs between traits are identified and discussed. The resulting picture, while incomplete, highlights key knowledge gaps that need to be filled to enable new models for predicting strain-level dynamics, which influence the development, toxicity and cosmopolitan nature of Microcystis blooms.

Tracing the active genetic diversity of Microcystis and Microcystis phage through a temporal survey of Taihu

Harmful algal blooms are commonly thought to be dominated by a single genus, but they are not homogenous communities. Current approaches, both molecular and culture-based, often overlook fine-scale variations in community composition that can influence bloom dynamics. We combined homology-based searches (BLASTX) and phylogenetics to distinguish and quantify Microcystis host and phage members across a summer season during a 2014 Microcystis- dominated bloom that occurred in Lake Tai (Taihu), China. We found 47 different genotypes of the Microcystis-specific DNA-dependent RNA polymerase (rpoB), which included several morphospecies. Microcystis flos-aquae and Microcystis wesenbergii accounted for ~86% of total Microcystis transcripts, while the more commonly studied Microcystis aeruginosa only accounted for ~7%. Microcystis genotypes were classified into three temporal groups according to their expression patterns across the course of the bloom: early, constant and late. All Microcystis morphospecies were present in each group, indicating that expression patterns were likely dictated by competition driven by environmental factors, not phylogeny. We identified three primary Microcystis-infecting phages based on the viral terminase, including a novel Siphoviridae phage that may be capable of lysogeny. Within our dataset, Myoviridae phages consistent with those infecting Microcystis in a lytic manner were positively correlated to the early host genotypes, while the Siphoviridae phages were positively correlated to the late host genotypes, when the Myoviridae phages express putative genetic markers for lysogeny. The expression of genes in the microcystin-encoding mcy cassette was estimated using mcyA, which revealed 24 Microcystis-specific genotypes that were negatively correlated to the early host genotypes. Of all environmental factors measured, pH best described the temporal shift in the Microcystis community genotypic composition, promoting hypotheses regarding carbon concentration mechanisms and oxidative stress. Our work expounds on the complexity of HAB events, using a well-studied dataset to highlight the need for increased resolution of community dynamics.

Cyanobacterial blooms in wastewater treatment facilities: Significance and emerging monitoring strategies

Municipal wastewater treatment facilities (WWTFs) are prone to the proliferation of cyanobacterial species which thrive in stable, nutrient-rich environments. Dense cyanobacterial blooms frequently disrupt treatment processes and the supply of recycled water due to their production of extracellular polymeric substances, which hinder microfiltration, and toxins, which pose a health risk to end-users. A variety of methods are employed by water utilities for the identification and monitoring of cyanobacteria and their toxins in WWTFs, including microscopy, flow cytometry, ELISA, chemoanalytical methods, and more recently, molecular methods. Here we review the literature on the occurrence and significance of cyanobacterial blooms in WWTFs and discuss the pros and cons of the various strategies for monitoring these potentially hazardous events. Particular focus is directed towards next-generation metagenomic sequencing technologies for the development of site-specific cyanobacterial bloom management strategies. Long-term multi-omic observations will enable the identification of indicator species and the development of site-specific bloom dynamics models for the mitigation and management of cyanobacterial blooms in WWTFs. While emerging metagenomic tools could potentially provide deep insight into the diversity and flux of problematic cyanobacterial species in these systems, they should be considered a complement to, rather than a replacement of, quantitative chemoanalytical approaches.

Seasonal dynamics of the bacterial communities associated with cyanobacterial blooms in the Han River

DNA-based analyses of bacterial communities were performed to identify the bacteria co-occurring with cyanobacterial blooms in samples collected at a single site over 2 years. Microcystis aeruginosa was the most predominant species (81% in 2018, and 94% in 2019) within the phylum Cyanobacteria, and microcystins were detected during all cyanobacterial blooms. The stereo microscope and scanning electron microscope observations showed bacterial associations on and around the aggregated M. aeruginosa cells. Culture-independent analyses of filtered bacterial communities showed that the Flavobacterium species in phylum Bacteroidetes (19%) was dominant in the cyanobacterial phycosphere, followed by the Limnohabitans species in Betaproteobacteria (11%). Using principal component analysis, major bacterial genus, including Microcystis and Flavobacterium species, were clustered during cyanobacterial blooms in both years. To identify key bacterial species that develop long-term symbiosis with M. aeruginosa, another culture-independent analysis was performed after the environmental sample had been serially subcultured for 1 year. Interestingly, Brevundimonas (14%) was the most dominant species, followed by Porphyrobacter (7%) and Rhodobacter (3.5%) within the Alphaproteobacteria. Screening of 100 colonies from cyanobacterial bloom samples revealed that the majority of culturable bacteria belonged to Gammaproteobacteria (28%) and Betaproteobacteria (57%), including Pseudomonas, Curvibacter, and Paucibacter species. Several isolates of Brevundimonas, Curvibacter, and Pseudomonas species could promote the growth of axenic M. aeruginosa PCC7806. The sensitivity of M. aeruginosa PCC7806 cells to different environmental conditions was monitored in bacteria-free pristine freshwater, indicating that nitrogen addition promotes the growth of M. aeruginosa.

Cyanobacterial Abundance and Microcystin Profiles in Two Southern British Lakes: The Importance of Abiotic and Biotic Interactions

Freshwater cyanobacteria blooms represent a risk to ecological and human health through induction of anoxia and release of potent toxins; both conditions require water management to mitigate risks. Many cyanobacteria taxa may produce microcystins, a group of toxic cyclic heptapeptides. Understanding the relationships between the abiotic drivers of microcystins and their occurrence would assist in the implementation of targeted, cost-effective solutions to maintain safe drinking and recreational waters. Cyanobacteria and microcystins were measured by flow cytometry and liquid chromatography coupled to tandem mass spectrometry in two interconnected reservoirs varying in age and management regimes, in southern Britain over a 12-month period. Microcystins were detected in both reservoirs, with significantly higher concentrations in the southern lake (maximum concentration >7 µg L^-1). Elevated microcystin concentrations were not positively correlated with numbers of cyanobacterial cells, but multiple linear regression analysis suggested temperature and dissolved oxygen explained a significant amount of the variability in microcystin across both reservoirs. The presence of a managed fishery in one lake was associated with decreased microcystin levels, suggestive of top down control on cyanobacterial populations. This study supports the need to develop inclusive, multifactor holistic water management strategies to control cyanobacterial risks in freshwater bodies.

Improved detection of mcyA genes and their phylogenetic origins in harmful algal blooms

Microcystins, a group of cyanotoxins produced by cyanobacterial strains, have become a significant microbial hazard to human and animal health due to increases in the frequency and intensity of cyanobacterial harmful algal blooms (CyanoHABs). Many studies have explored the correlation between microcystin concentrations and abundances of toxin-producing genes (e.g., mcyA genes) measured using quantitative PCR, and discrepancies between toxin concentrations and gene abundances are often observed. In this study, the results show that these discrepancies are at least partially due to primer sets that do not capture the phylogenetic diversity of naturally present toxin-producers. We designed three novel primer gene probes based on known mcyA genes to improve the detection and quantification of these genes in environmental samples. These primers were shown to improve the identification of mcyA genes compared to previously published primers in freshwater metagenomes, cyanobacterial isolates, and lake water samples. Unlike previously published primers, our primer sets could selectively amplify and resolve Microcystis, Anabaena, and Planktothrix mcyA genes. In lake water samples, abundance estimations of mcyA genes were found to correlate strongly with microcystin concentrations. Based on our results, these primers offer significant improvements over previously published probes to accurately identify and quantify mcyA genes in the environment. There is an increasing need to develop models based on microbial information and environmental factors to predict CyanoHABs, and improved primers will play an important role in aiding monitoring efforts to collect reliable and consistent data on toxicity risks.

Utility of a PCR-based method for rapid and specific detection of toxigenic Microcystis spp. in farm ponds

Microcystis is a widespread freshwater cyanobacterium that can produce microcystin, a potent hepatotoxin harmful to animals and humans. Therefore, it is crucial to monitor for the presence of toxigenic Microcystis spp. to provide early warning of potential microcystin contamination. Microscopy, which has been used traditionally to identify Microcystis spp., cannot differentiate toxigenic from non-toxigenic Microcystis. We developed a PCR-based method to detect toxigenic Microcystis spp. based on detection of the microcystin synthetase C (mcyC) gene and 16S rRNA gene. Specificity was validated against toxic and nontoxic M. aeruginosa strains, as well as 4 intergeneric freshwater cyanobacterial strains. Analytical sensitivity was as low as 747 fg/µL genomic DNA (or 3 cells/µL) for toxic M. aeruginosa. Furthermore, we tested 60 water samples from 4 farm ponds providing drinking water to swine facilities in the midwestern United States using this method. Although all water samples were positive for Microcystis spp. (i.e., 16S rRNA gene), toxigenic Microcystis spp. were detected in only 34 samples (57%). Seventeen water samples contained microcystin (0.1-9.1 μg/L) determined with liquid chromatography-mass spectrometry, of which 14 samples (82%) were positive for mcyC. A significant correlation was found between the presence of toxigenic Microcystis spp. and microcystin in water samples (p = 0.0004). Our PCR method can be a low-cost molecular tool for rapid and specific identification of toxigenic Microcystis spp. in farm ponds, improving detection of microcystin contamination, and ensuring water safety for farm animals.

Antibiotic resistance genes and microcystins in a drinking water treatment plant

Problems with antibiotic resistance genes (ARGs) and secondary pollution from microcystins (MCs), caused by cyanobacterial blooms have become significant global issues. These two pollutants co-occur in drinking water treatment plants (DWTPs), but the exact relationships between them requires further clarification. Here, a high-throughput quantitative real-time PCR and enzyme-linked immunosorbent assay were used to investigate the behavior of ARGs and MCs in a practical DWTP in the first place. After the on-site investigation, the effect of MCs on the horizontal transfer of ARGs was studied under laboratory conditions, and mechanisms explored at both cellular and molecular levels. MCs could promote the spread of ARGs, especially in relatively stationary and stable environments such as biofilms. MC-LR was the most efficient microcystin subtype promoting conjugative transfer, which was 25.13 times higher than for the control group. MCs affected the horizontal transfer of ARGs by regulating a series of gene systems involved in conjugative transfer, stimulating the formation of reactive oxygen species (ROS), and increasing cell membrane permeability. This study can provide a theoretical basis for the control of ARGs and MCs in DWTPs, which is of great significance for the scientific assessment of drinking water safety.

Use of qPCR and RT-qPCR for monitoring variations of microcystin producers and as an early warning system to predict toxin production in an Ohio inland lake

Public concern over cyanobacterial blooms has increased due to their higher frequency of occurrence and their potential ecological and health impacts. Detection of microcystin (MC) producers (MCPs) using qPCR and RT-qPCR allows for the rapid identification of blooms by combining specificity and sensitivity with a relatively high throughput capability. Investigation of MCP population composition (correlation, dominance), toxin gene expression, and relationship to MC concentration was conducted using a panel of qPCR assays targeting mcyA, E and G on weekly and daily water samples collected from an Ohio inland reservoir lake. Further, these data were used to develop early warning thresholds for prediction of MC concentrations exceeding the US EPA Health Advisory cutoff value (>0.3 μg L-1) using receiver operating characteristic curves and tobit regression. MCP Microcystis genomic copy number made up approximately 35% of the total Microcystis spp. and was the dominant toxic subpopulation of MCPs. The expressed MCPs were 0.2% of the extant genomic copy numbers, while toxic Microcystis had higher expressed proportion (0.5%) than that of toxic Planktothrix (0.04%). Microcystis toxin genes increased in June and July but decreased in August and September along with similar trends of cell replication. Quantities of both RT-qPCR and qPCR followed the same trend and were highly correlated with MC-ADDA, while RT-qPCR not only reflected the active toxin genes or toxic species, but also indicated the beginning and ending of toxin production. A one-week early warning of MC exceedance over the EPA Health Advisory was based on signaling of qPCR and RT-qPCR using receiver operating characteristic curves. This study illustrates the potential use of qPCR or RT-qPCR as an early warning system of extant and MC producing potentials during a toxic algal bloom, with predictive powers of 50%-60% and 30%-40% (p < 0.001), respectively, and false positive rates of about 70% for both LC-MS/MS or ELISA.

Culture-independent and culture-dependent analyses of the bacterial community in the phycosphere of cyanobloom-forming Microcystis aeruginosa

Confocal and scanning electron microscopic observations have previously shown the strong bacterial association of Microcystis aeruginosa cells on their surfaces. DNA-based analyses of the associated bacterial communities were carried out using two M. aeruginosa strains grown in the laboratory and eight newly collected cyanobacterial bloom samples. M. aeruginosa was the most predominant species (66–100%) within the phylum Cyanobacteria. Rhizobium, Hydrogenophaga and Brevundimonas species were commonly found, and Flavobacterium species were present in all the cyanobacterial bloom samples. In total, 396 colonies from various samples were screened, revealing that most culturable bacteria belonged to the class Alphaproteobacteria (19%) including Rhizobium, Brevundimonas, and Porphyrobacter species. The genetic variation among the M. aeruginosa strains and different habitat conditions may have led to the presence of distinct bacterial populations among the tested samples. Among all the tested seven culturable isolates, Rhizobium sp. MK23 showed the best growth-promotion effect on the axenic M. aeruginosa strains. H₂O₂ was observed to be produced during the growth of M. aeruginosa PCC7806 under light conditions, this strain was more resistant to H₂O₂ when associated with Rhizobium sp. MK23. Our data suggested that Rhizobium species along with other associated bacteria might help the growth of M. aeruginosa by decomposing H₂O₂ under the aerobic growing conditions.

Coherence of Microcystis species revealed through population genomics

Microcystis is a genus of freshwater cyanobacteria, which causes harmful blooms in ecosystems worldwide. Some Microcystis strains produce harmful toxins such as microcystin, impacting drinking water quality. Microcystis colony morphology, rather than genetic similarity, is often used to classify Microcystis into morphospecies. Yet colony morphology is a plastic trait, which can change depending on environmental and laboratory culture conditions, and is thus an inadequate criterion for species delineation. Furthermore, Microcystis populations are thought to disperse globally and constitute a homogeneous gene pool. However, this assertion is based on relatively incomplete characterization of Microcystis genomic diversity. To better understand these issues, we performed a population genomic analysis of 33 newly sequenced genomes mainly from Canada and Brazil. We identified 17 Microcystis clusters of genomic similarity, five of which correspond to monophyletic clades containing at least three newly sequenced genomes. Four out of these five clades match to named morphospecies. Notably, M. aeruginosa is paraphyletic, distributed across 12 genomic clusters, suggesting it is not a coherent species. A few clades of closely related isolates are specific to a unique geographic location, suggesting biogeographic structure over relatively short evolutionary time scales. Higher homologous recombination rates within than between clades further suggest that monophyletic groups might adhere to a Biological Species-like concept, in which barriers to gene flow maintain species distinctness. However, certain genes-including some involved in microcystin and micropeptin biosynthesis-are recombined between monophyletic groups in the same geographic location, suggesting local adaptation.

Flow Cytometric Analysis of Freshwater Cyanobacteria: A Case Study

Eutrophication is a process that occurs due to the excessive accumulation of nutrients, primarily nitrogen and phosphorus, from natural and anthropogenic sources. This phenomenon causes cyanobacterial overgrowth, which over time leads to cyanobacterial harmful algal blooms (CHABs) that affect public drinking water sources and water sites with recreational usage. The rapid detection of bloom-forming cyanobacteria in freshwater bodies is critical in order to implement prevention strategies. Cyanobacteria contain phycobiliproteins such as phycoerythrin and allophycocyanin as part of the phycobilisome that allows autofluorescence. In this study, samples from 36 freshwater bodies in 14 New Jersey counties were collected and analyzed using flow cytometry with forward-scatter phycoerythrin and allophycocyanin parameters. Pure cultures of Synechococcus sp. IU 625, Cylindrospermum spp. and Microcystis aeruginosa were used as references. The results revealed that 17 out of the 36 analyzed sites contained all three references and related species. Seven sites showed Microcystis and Cylindrospermum-like species, while four sites indicated Microcystis and Cylindrospermum-like species. Six water bodies showed Cylindrospermum-like species, and two sites showed Microcystis-like species. Polymerase chain reaction (PCR)-based assays further confirmed the flow cytometric results. The findings from this study suggest that flow cytometry could potentially serve as a rapid method for freshwater cyanobacteria detection and screening.

Interaction between cyanophage MaMV-DC and eight Microcystis strains, revealed by genetic defense systems

Cyanophage MaMV-DC is a member of Myoviridae that was reported to specifically infect and lyse Microcystis aeruginosa FACHB-524 among 21 selected cyanobacterial strains. We reidentified the infection specificity of MaMV-DC among seven other Microcystis strains of different species. In our experiments, MaMV-DC infected three Microcystis strains but did not form plaque in Microcystis lawns. This indicated that MaMV-DC is at least a genus- rather than strain-specific virus. Cyanophage MaMV-DC genes were transcribed in M. aeruginosa FACHB-524, M. flos-aquae TF09, M. aeruginosa TA09 and M. wesenbergii DW09, and the growth of these Microcystis strains was inhibited by the addition of MaMV-DC. The predicted defense of eight Microcystis strains by CRISPR-Cas systems has shown mixed consistency with the infection experiment results, suggesting other defense or anti-defense systems play roles during infection process. Restriction-modification (RM) system analysis revealed an abundance of four types of RM proteins that may play roles in defense against cyanophages.

Global Metabolomic Characterizations of Microcystis spp. Highlights Clonal Diversity in Natural Bloom-Forming Populations and Expands Metabolite Structural Diversity

Cyanobacteria are photosynthetic prokaryotes capable of synthesizing a large variety of secondary metabolites that exhibit significant bioactivity or toxicity. Microcystis constitutes one of the most common cyanobacterial genera, forming the intensive blooms that nowadays arise in freshwater ecosystems worldwide. Species in this genus can produce numerous cyanotoxins (i.e., toxic cyanobacterial metabolites), which can be harmful to human health and aquatic organisms. To better understand variations in cyanotoxin production between clones of Microcystis species, we investigated the diversity of 24 strains isolated from the same blooms or from different populations in various geographical areas. Strains were compared by genotyping with 16S-ITS fragment sequencing and metabolite chemotyping using LC ESI-qTOF mass spectrometry. While genotyping can help to discriminate among different species, the global metabolome analysis revealed clearly discriminating molecular profiles among strains. These profiles could be clustered primarily according to their global metabolite content, then according to their genotype, and finally according to their sampling location. A global molecular network of all metabolites produced by Microcystis species highlights the production of a wide set of chemically diverse metabolites, including a few microcystins, many aeruginosins, microginins, cyanopeptolins, and anabaenopeptins, together with a large set of unknown molecules. These components, which constitute the molecular biodiversity of Microcystis species, still need to be investigated in terms of their structure and potential bioactivites (e.g., toxicity).

Application of Bayesian network including Microcystis morphospecies for microcystin risk assessment in three cyanobacterial bloom-plagued lakes, China

Microcystis spp., which occur as colonies of different sizes under natural conditions, have expanded in temperate and tropical freshwater ecosystems and caused seriously environmental and ecological problems. In the current study, a Bayesian network (BN) framework was developed to access the probability of microcystins (MCs) risk in large shallow eutrophic lakes in China, namely, Taihu Lake, Chaohu Lake, and Dianchi Lake. By means of a knowledge-supported way, physicochemical factors, Microcystis morphospecies, and MCs were integrated into different network structures. The sensitive analysis illustrated that Microcystis aeruginosa biomass was overall the best predictor of MCs risk, and its high biomass relied on the combined condition that water temperature exceeded 24 °C and total phosphorus was above 0.2 mg/L. Simulated scenarios suggested that the probability of hazardous MCs (≥1.0 μg/L) was higher under interactive effect of temperature increase and nutrients (nitrogen and phosphorus) imbalance than that of warming alone. Likewise, data-driven model development using a naïve Bayes classifier and equal frequency discretization resulted in a substantial technical performance (CCI = 0.83, K = 0.60), but the performance significantly decreased when model excluded species-specific biomasses from input variables (CCI = 0.76, K = 0.40). The BN framework provided a useful screening tool to evaluate cyanotoxin in three studied lakes in China, and it can also be used in other lakes suffering from cyanobacterial blooms dominated by Microcystis.

Tile Drainage and Anthropogenic Land Use Contribute to Harmful Algal Blooms and Microbiota Shifts in Inland Water Bodies

Freshwater harmful algal blooms (HABs), driven by nutrient inputs from anthropogenic sources, pose unique risks to human and ecological health worldwide. A major nutrient contributor is agricultural land use, specifically tile drainage discharge. Small lakes and ponds are at elevated risk for HAB appearance, as they are uniquely sensitive to nutrient input. HABs introduce exposure risk to microcystin (MC), hepatotoxic and potentially carcinogenic cyanotoxins. To investigate the impact of anthropogenic land use on small lakes and ponds, 24 sites in central Ohio were sampled over a 3-month period in late summer of 2015. MC concentration, microbial community structure, and water chemistry were analyzed. Land use intensity, including tile drainage systems, was the driver of clustering in principle component analysis, ultimately contributing to nutrient deposition, a driver of HABs. Relative abundance of HAB-forming genera was correlated with elevated concentrations of nitrate and soluble reactive phosphate. One location (FC) showed MC concentrations exceeding 875 μg/L and large community shifts in ciliates (Oligohymenophorea) associated with hypoxic conditions. The prokaryotic community at FC was dominated by Planktothrix sp. These results demonstrate the impact of HABs in small lakes and ponds, and that prevailing issues extend beyond cyanotoxins, such as cascading impacts on other trophic levels.

Stepwise strategy for monitoring toxic cyanobacterial blooms in lentic water bodies

Climate change has been causing the increase in frequency, severity, and duration of harmful algal blooms, which makes the establishment of water management strategies indispensable. For cyanobacteria, several methods are currently used in monitoring programs. However, these methods are time-consuming and require specialists, and results are usually not provided within an adequate timeframe for taking timely mitigation actions. This work proposes a strategy for a faster, easier, and more cost-effective monitoring of cyanobacterial blooms, using a stepwise approach based on fluorometric determination of phycocyanin at an early stage. Complementary parameters (chlorophyll a, enumeration of dominant cyanobacterial species and cyanotoxin potential and quantification) are determined when necessary, thus progressively allocating human and financial resources within the monitoring program. This strategy was applied and validated using nine lentic eutrophic freshwater bodies prone to the occurrence of cyanobacterial blooms. Samples were sequentially evaluated, and the study ended up with two samples that showed high health risks. However, according to WHO guidelines, eight of the nine samples would be classified as having "moderate risk of adverse health effects" and could lead to preventive measures that would have an important regional economic impact. Therefore, the present approach proved to be a promising alternative to increase the effectiveness and accuracy of the risk assessment process in water bodies where cyanobacterial blooms occur.

Genome sequences of lower Great Lakes Microcystis sp. reveal strain-specific genes that are present and expressed in western Lake Erie blooms

Blooms of the potentially toxic cyanobacterium Microcystis are increasing worldwide. In the Laurentian Great Lakes they pose major socioeconomic, ecological, and human health threats, particularly in western Lake Erie. However, the interpretation of "omics" data is constrained by the highly variable genome of Microcystis and the small number of reference genome sequences from strains isolated from the Great Lakes. To address this, we sequenced two Microcystis isolates from Lake Erie (Microcystis aeruginosa LE3 and M. wesenbergii LE013-01) and one from upstream Lake St. Clair (M. cf aeruginosa LSC13-02), and compared these data to the genomes of seventeen Microcystis spp. from across the globe as well as one metagenome and seven metatranscriptomes from a 2014 Lake Erie Microcystis bloom. For the publically available strains analyzed, the core genome is ~1900 genes, representing ~11% of total genes in the pan-genome and ~45% of each strain's genome. The flexible genome content was related to Microcystis subclades defined by phylogenetic analysis of both housekeeping genes and total core genes. To our knowledge this is the first evidence that the flexible genome is linked to the core genome of the Microcystis species complex. The majority of strain-specific genes were present and expressed in bloom communities in Lake Erie. Roughly 8% of these genes from the lower Great Lakes are involved in genome plasticity (rapid gain, loss, or rearrangement of genes) and resistance to foreign genetic elements (such as CRISPR-Cas systems). Intriguingly, strain-specific genes from Microcystis cultured from around the world were also present and expressed in the Lake Erie blooms, suggesting that the Microcystis pangenome is truly global. The presence and expression of flexible genes, including strain-specific genes, suggests that strain-level genomic diversity may be important in maintaining Microcystis abundance during bloom events.

Cytomorphological and nitrogen metabolic enzyme analysis of psychrophilic and mesophilic Nostoc sp.: a comparative outlook

Cyanobacterial diazotrophs play a significant role in environmental nitrogen economy despite their habitat either tropical or polar. However, the phenomenon by which it copes with temperature induced stress is poorly understood. Temperature response study of psychrophilic and mesophilic Nostoc strains explores their adaptive mechanisms. The selected psychrophilic and mesophilic strains were confirmed as Nostoc punctiforme and Nostoc calcicola respectively, by ultrastructure and 16S rDNA phylogeny. The psychrophilic strain has extensive glycolipid and polysaccharide sheath along with characteristic deposition of cyanophycin, polyhydroxybutyrate granules, and carboxysomes. This is possibly an adaptive strategy exhibited to withstand the freezing temperature and high intense of ultraviolet rays. The biomass measured in terms of dry weight, protein, and chlorophyll indicated a temperature dependant shift in both the psychrophilic and mesophilic strains and attained maximum growth in their respective temperature niches. At low temperature, psychrophilic organism exhibited nitrogenase activity, while mesophilic strains did not. The maximum glutamine synthetase activity was observed at 4 °C for psychrophilic and 37 °C for mesophilic strains. Activity at 4 °C in psychrophilic strains revealed their energetic mechanism even at low temperature. The nitrate and nitrite reductase of both psychrophilic and mesophilic strains showed maximum activity at 37 °C denoting their similar nitrogen assimilating mechanisms for combined nitrogen utilization. The activity studies of nitrogen fixation/assimilation enzymes have differential effects at varying temperatures, which provide valuable insights of physiological contribution and role of Nostoc strains in the biological nitrogen cycle.

A qPCR-Based Tool to Diagnose the Presence of Harmful Cyanobacteria and Cyanotoxins in Drinking Water Sources

Harmful cyanobacteria have been an important concern for drinking water quality for quite some time, as they may produce cyanotoxins and odorants. Microcystis and Cylindrospermopsis are two common harmful cyanobacterial genera detected in freshwater lakes and reservoirs, with microcystins (MCs) and cylindrospermopsin (CYN) as their important metabolites, respectively. In this study, two sets of duplex qPCR systems were developed, one for quantifying potentially-toxigenic Microcystis and Microcystis, and the other one for cylindrospermopsin-producing cyanobacteria and Cylindrospermopsis. The duplex qPCR systems were developed and validated in the laboratory by using 338 samples collected from 29 reservoirs in Taiwan and her offshore islands. Results show that cell numbers of Microcystis and Cylindorspermopsis enumerated with microscopy, and MCs and CYN concentrations measured with the enzyme-linked immuno-sorbent assay method, correlated well with their corresponding gene copies determined with the qPCR systems (range of coefficients of determination R² = 0.392−0.740). The developed qPCR approach may serve as a useful tool for the water industry to diagnose the presence of harmful cyanobacteria and the potential presence of cyanotoxins in source waters.

Genetic divergence among toxic and non-toxic cyanobacteria of the dry zone of Sri Lanka

Sri Lanka has rich cyanobacterial diversity, however, only few studies have been conducted to identify the potential toxin producers in water bodies used for human consumption. As the detection of cyanotoxin is vital in water quality management, a study was done by employing 16S rRNA gene to explore the genetic divergence, phylogenetic relationships and potential toxin producing cyanobacteria in reservoirs and well waters in the dry zone of Sri Lanka. Forty five, 16S rRNA gene sequences were assayed and phylogenetic tree was constructed. Among 45 isolates, 20 isolates were classified as unidentified cyanobacteria and considered as novel cyanobacterial genera. Of 25 identified isolates, seven isolates were identified up to species level. With 16S rRNA phylogeny, 20 unidentified cyanobacterial isolates were able to place on their taxonomic positions up to order level. Results revealed that water samples understudy had vast cyanobacterial diversity with potential microcystin (MC) and cylindrospermopsin (CYN) producers and eleven clusters clearly demonstrated five cyanobacterial orders with more than 90% similarity irrespective to their toxicity which showed the suitability of 16S rRNA gene for taxonomic differentiation. Sixteen isolates had the potential to produce MC and two isolates to produce CYN. Findings of the study confirm the rich cyanobacterial diversity and the divergence among the potential cyanotoxin producers in the dry zone water bodies of Sri Lanka.

Fluorescence in situ hybridization of Microcystis strains producing microcystin using specific mRNA probes

Cyanobacteria are ubiquitous micro-organisms that can produce toxic compounds, the cyanotoxins. The monitoring of such producers in the environment is of prime importance for human health. An attractive technology for such monitoring is fluorescence in situ hybridization (FISH), which allows the detection and enumeration of environmental micro-organisms. We present here the application of tyramide signal amplification fluorescence in situ hybridization (TSA-FISH) to the detection of microcystin-producing Microcystis strains. We used a 16S rRNA-specific probe, MICR3, to specifically label and observe by epifluorescence microscopy Microcystis aeruginosa strains. Using confocal laser scanning microscopy and a specific probe, MCYA, targeting the mcyA mRNA we have labelled M. aeruginosa PCC 7806, which produces microcystins. Microcystis aeruginosa PCC 7005 which does not produce microcystins is not labelled by this probe. Furthermore, we show here that this specific mRNA labelling in M. aeruginosa PCC 7806 is enhanced in cells illuminated for 1 h just after a dark period of cultivation of 24 h, conditions in which the mcyA gene is up regulated. The data presented here might be applicable to the monitoring of toxic Microcystis strains in the environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

Cyanobacteria producing toxic compounds (cyanotoxins) are present in the environment and in water bodies. Their presence poses a threat on human and animal health. It is thus important to detect, identify and enumerate these toxic Cyanobacteria. Using tyramide signal amplification fluorescence in situ hybridization (TSA-FISH) and specific probes, with confocal laser scanning microscopy, we have specifically detected Microcystis strains producing microcystin toxins. The data presented here might be applied to the monitoring of water bodies at early stages and all along the formation of Microcystis blooms.

Is qPCR a Reliable Indicator of Cyanotoxin Risk in Freshwater?

The wide distribution of cyanobacteria in aquatic environments leads to the risk of water contamination by cyanotoxins, which generate environmental and public health issues. Measurements of cell densities or pigment contents allow both the early detection of cellular growth and bloom monitoring, but these methods are not sufficiently accurate to predict actual cyanobacterial risk. To quantify cyanotoxins, analytical methods are considered the gold standards, but they are laborious, expensive, time-consuming and available in a limited number of laboratories. In cyanobacterial species with toxic potential, cyanotoxin production is restricted to some strains, and blooms can contain varying proportions of both toxic and non-toxic cells, which are morphologically indistinguishable. The sequencing of cyanobacterial genomes led to the description of gene clusters responsible for cyanotoxin production, which paved the way for the use of these genes as targets for PCR and then quantitative PCR (qPCR). Thus, the quantification of cyanotoxin genes appeared as a new method for estimating the potential toxicity of blooms. This raises a question concerning whether qPCR-based methods would be a reliable indicator of toxin concentration in the environment. Here, we review studies that report the parallel detection of microcystin genes and microcystin concentrations in natural populations and also a smaller number of studies dedicated to cylindrospermopsin and saxitoxin. We discuss the possible issues associated with the contradictory findings reported to date, present methodological limitations and consider the use of qPCR as an indicator of cyanotoxin risk.

Rapid Classification and Identification of Microcystis aeruginosa Strains Using MALDI-TOF MS and Polygenetic Analysis

Matrix-assisted laser desorption-ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was used to establish a rapid, simple, and accurate method to differentiate among strains of Microcystis aeruginosa, one of the most prevalent types of bloom-forming cyanobacteria. M. aeruginosa NIES-843, for which a complete genome has been sequenced, was used to characterize ribosomal proteins as biomarkers and to optimize conditions for observing ribosomal proteins as major peaks in a given mass spectrum. Thirty-one of 52 ribosomal subunit proteins were detected and identified along the mass spectrum. Fifty-five strains of M. aeruginosa from different habitats were analyzed using MALDI-TOF MS; among these samples, different ribosomal protein types were observed. A polygenetic analysis was performed using an unweighted pair-group method with arithmetic means and different ribosomal protein types to classify the strains into five major clades. Two clades primarily contained toxic strains, and the other three clades contained exclusively non-toxic strains. This is the first study to differentiate cyanobacterial strains using MALDI-TOF MS.

Comparative summer dynamics of surface cyanobacterial communities in two connected lakes from the west of Ireland

The eutrophication of lakes is typically associated with high biomass proliferations of potentially toxic cyanobacteria. At a regional level, the sustainable management of water resources necessitates an approach that recognises the interconnectivity of multiple water systems within river catchments. This study examined the dynamics in summer diversity of planktonic cyanobacterial communities and microcystin toxin concentrations in two inter-connected lakes from the west of Ireland prone to nutrient enrichment. DGGE analysis of 16S rRNA gene amplicons of genotype-I cyanobacteria (typically spherical) showed changes in the communities of both Lough Corrib and Ballyquirke Lough throughout the summer, and identified cyanobacterial genotypes both unique and shared to both lakes. Microcystin concentrations, estimated via the protein phosphatase 2A inhibition assay, were greater in August than in July and June in both lakes. This was concomitant to the increased occurrence of Microcystis as evidenced by DGGE band excision and subsequent sequencing and BLAST analysis. RFLP analysis of PCR amplified mcy-A/E genes clustered together the August samples of both lakes, highlighting a potential change in microcystin producers across the two lakes. Finally, the multiple factor analysis of the combined environmental data set for the two lakes highlighted the expected pattern opposing greater water temperature and chlorophyll concentration against macronutrient concentrations, but also indicated a negative relationship between microcystin concentration and cyanobacterial diversity, possibly underlining allelopathic interactions. Despite some element of connectivity, the dissimilarity in the composition of the cyanobacterial assemblages and the timing of community change in the two lakes likely were a reflexion of niche differences determined by meteorologically-forced variation in physico-chemical parameters in the two water bodies.

Distribution and Habitat Specificity of Potentially-Toxic Microcystis across Climate, Land, and Water Use Gradients

Toxic cyanobacterial blooms are a growing threat to freshwater bodies worldwide. In order for a toxic bloom to occur, a population of cells with the genetic capacity to produce toxins must be present together with the appropriate environmental conditions. In this study, we investigated the distribution patterns and phylogeny of potentially-toxic Microcystis (indicated by the presence and/or phylogeny of the mcyD and mcyA genes). Samples were collected from the water column of almost 60 water bodies across widely differing gradients of environmental conditions and land use in Israel. Potentially, toxic populations were common but not ubiquitous, detected in ~65% of the studied sites. Local environmental factors, including phosphorus and ammonia concentrations and pH, as well as regional conditions such as the distance from built areas and nature reserves, were correlated with the distribution of the mcyD gene. A specific phylogenetic clade of Microcystis, defined using the sequence of the mcyA gene, was preferentially associated with aquaculture facilities but not irrigation reservoirs. Our results reveal important environmental, geospatial, and land use parameters affecting the geographic distribution of toxinogenic Microcystis, suggesting non-random dispersal of these globally abundant toxic cyanobacteria.

Extracellular microcystin prediction based on toxigenic Microcystis detection in a eutrophic lake

Existing models for predicting microcystin concentration in water body generally use chlorophyll or cyanobacteria concentration as input variables, although microcystins only originate from toxigenic strains of a few species. Moreover, the nonconcurrency between harmful algal growth and toxin release has yet to be quantified. Therefore, this study explored a new prediction method that considers these toxin production mechanisms for the eutrophic Yangcheng Lake, a large-scale drinking water source in China. The Lake was monitored weekly at six sampling sites from July to October in 2012, including the detection of toxigenic Microcystis (expressed as mcyA copy number) by qPCR. Compared with chlorophyll a, cyanobacteria, and total Microcystis abundance, toxigenic Microcystis concentration was more significant in predicting extracellular microcystin. Site-specific nonlinear regression models that link mcyA to microcystins were established. Parameters for toxin release delay (i.e., one or two weeks) were embedded in these models. Further analysis ascribed the different release timescale to NH₃-N:TN and TN:TP ratios of approximately 0.015 and 9.2, respectively, which may decrease the delay in microcystin release. Model applications in determining mcyA monitoring frequency and its warning thresholds were discussed.

Specific Gene Loci of Clinical Pseudomonas putida Isolates

Pseudomonas putida are ubiquitous inhabitants of soils and clinical isolates of this species have been seldom described. Clinical isolates show significant variability in their ability to cause damage to hosts because some of them are able to modulate the host’s immune response. In the current study, comparisons between the genomes of different clinical and environmental strains of P. putida were done to identify genetic clusters shared by clinical isolates that are not present in environmental isolates. We show that in clinical strains specific genes are mostly present on transposons, and that this set of genes exhibit high identity with genes found in pathogens and opportunistic pathogens. The set of genes prevalent in P. putida clinical isolates, and absent in environmental isolates, are related with survival under oxidative stress conditions, resistance against biocides, amino acid metabolism and toxin/antitoxin (TA) systems. This set of functions have influence in colonization and survival within human tissues, since they avoid host immune response or enhance stress resistance. An in depth bioinformatic analysis was also carried out to identify genetic clusters that are exclusive to each of the clinical isolates and that correlate with phenotypical differences between them, a secretion system type III-like was found in one of these clinical strains, a determinant of pathogenicity in Gram-negative bacteria.

Multi-Year Assessment of Toxic Genotypes and Microcystin Concentration in Northern Lake Taihu, China

Lake Taihu is the third-largest freshwater lake in China and has been suffering from cyanobacterial blooms for over two decades. The northern part of the lake, Meiliang Bay, is known to be at high risk of dense and sustained Microcystis blooms and toxins. This study aimed to investigate and record the annual and seasonal dynamics of toxic genotype, Microcystis morphospecies succession and microcystin variation. It also aimed to find out the underlying driving factors influencing the dynamic changes. Microcystin (MC) and the Microcystis genotype were quantified using HPLC and quantitative real-time PCR, respectively. Our study, over three consecutive years, showed that the pattern of morphospecies succession was seasonally distinct and annually consistent. During the same period in 2012, 2013 and 2014, the average MC were, on dry weight basis, 733 μg·g⁻¹, 844 μg·g⁻¹, 870 μg·g⁻¹, respectively. The proportion of toxic Microcystis accounted for 41%, 44% and 52%, respectively. Cell bound microcystin was found to correlate with the percentage of toxic Microcystis. Based on historical and current data, we conclude that annual bloom toxicity was relatively stable or possibly increased over the last decade.

The dynamics of microcystis genotypes and microcystin production and associations with environmental factors during blooms in Lake Chaohu, China

Lake Chaohu, which is a large, shallow, hypertrophic freshwater lake in southeastern China, has been experiencing lake-wide toxic Microcystis blooms in recent decades. To illuminate the relationships between microcystin (MC) production, the genotypic composition of the Microcystis community and environmental factors, water samples and associated environmental data were collected from June to October 2012 within Lake Chaohu. The Microcystis genotypes and MC concentrations were quantified using quantitative real-time PCR (qPCR) and HPLC, respectively. The results showed that the abundances of Microcystis genotypes and MC concentrations varied on spatial and temporal scales. Microcystis exists as a mixed population of toxic and non-toxic genotypes, and the proportion of toxic Microcystis genotypes ranged from 9.43% to 87.98%. Both Pearson correlation and stepwise multiple regressions demonstrated that throughout the entire lake, the abundances of total and toxic Microcystis and MC concentrations showed significant positive correlation with the total phosphorus and water temperature, suggesting that increases in temperature together with the phosphorus concentrations may promote more frequent toxic Microcystis blooms and higher concentrations of MC. Whereas, dissolved inorganic carbon (DIC) was negatively correlated with the abundances of total and toxic Microcystis and MC concentrations, indicating that rising DIC concentrations may suppress toxic Microcystis abundance and reduce the MC concentrations in the future. Therefore, our results highlight the fact that future eutrophication and global climate change can affect the dynamics of toxic Microcystis blooms and hence change the MC levels in freshwater.

Methods to detect cyanobacteria and their toxins in the environment

Cyanobacteria blooms are since early times a cause for environmental concern because of their negative impact through the release of odors, water discoloration, and more dangerously through the release of toxic compounds (i.e. the cyanotoxins) that can affect both human and animal welfare. Surveillance of the aquatic ecosystems is therefore obligatory, and methods to achieve such require a prompt answer not only regarding the species that are producing the blooms but also the cyanotoxins that are being produced and/or released. Moreover, besides this well-known source of possible intoxication, it has been demonstrated the existence of several other potential routes of exposure, either for humans or other biota such as through food additives and in terrestrial environments (in plants, lichens, biological soil crusts) and the recognition of their harmful impact on less studied ecosystems (e.g. coral reefs). Nowadays, the most frequent approaches to detect toxic cyanobacteria and/or their toxins are the chemical-, biochemical-, and molecular-based methods. Above their particular characteristics and possible applications, they all bring to the environmental monitoring several aspects that are needed to be discussed and scrutinized. The end outcome of this review will be to provide newer insights and recommendations regarding the methods needed to apply in an environmental risk assessment program. Therefore, a current state of the knowledge concerning the three methodological approaches will be presented, while highlighting positive and negative aspects of each of those methods within the purpose of monitoring or studying cyanobacteria and their toxins in the environment.

Comparison of cyanobacterial microcystin synthetase (mcy) E gene transcript levels, mcy E gene copies, and biomass as indicators of microcystin risk under laboratory and field conditions

Increased incidences of mixed assemblages of microcystin-producing and nonproducing cyanobacterial strains in freshwater bodies necessitate development of reliable proxies for cyanotoxin risk assessment. Detection of microcystin biosynthetic genes in water blooms of cyanobacteria is generally indicative of the presence of potentially toxic cyanobacterial strains. Although much effort has been devoted toward elucidating the microcystin biosynthesis mechanisms in many cyanobacteria genera, little is known about the impacts of co-occurring cyanobacteria on cellular growth, mcy gene expression, or mcy gene copy distribution. The present study utilized conventional microscopy, qPCR assays, and enzyme-linked immunosorbent assay to study how competition between microcystin-producing Microcystis aeruginosa CPCC 299 and Planktothrix agardhii NIVA-CYA 126 impacts mcyE gene expression, mcyE gene copies, and microcystin concentration under controlled laboratory conditions. Furthermore, analyses of environmental water samples from the Missisquoi Bay, Quebec, enabled us to determine how the various potential toxigenic cyanobacterial biomass proxies correlated with cellular microcystin concentrations in a freshwater lake. Results from our laboratory study indicated significant downregulation of mcyE gene expression in mixed cultures of M. aeruginosa plus P. agardhii on most sampling days in agreement with depressed growth recorded in the mixed cultures, suggesting that interaction between the two species probably resulted in suppressed growth and mcyE gene expression in the mixed cultures. Furthermore, although mcyE gene copies and McyE transcripts were detected in all laboratory and field samples with measureable microcystin levels, only mcyE gene copies showed significant positive correlations (R(2) > 0.7) with microcystin concentrations, while McyE transcript levels did not. These results suggest that mcyE gene copies are better indicators of potential risks from microcystins than McyE transcript levels or conventional biomass proxies, especially in water bodies comprising mixed assemblages of toxic and nontoxic cyanobacteria.

Monitoring toxigenic Microcystis strains in the Missisquoi bay, Quebec, by PCR targeting multiple toxic gene loci

The increasing incidence of mixed assemblages of toxic and nontoxic cyanobacterial blooms in Quebec's freshwater bodies over the last decade, coupled with inherent inadequacies of current monitoring approaches, warrants development of sensitive and reliable tools for assessing the toxigenic potential of these water blooms. In this study, we applied three independent polymerase chain reaction (PCR) assays that simultaneously target the microcystin synthetase (mcy) genes A, E, and G to rapidly and reliably detect and quantify potentially toxic Microcystis genotypes in the Missisquoi bay, Quebec, Canada. Linear regressions of quantitative PCR threshold cycles (Ct ) against the logarithm of their respective Microcystis cell number equivalents resulted in highly significant linear curves with coefficients of determination (R(2) ) greater than 0.99 (p < 0.0001, n = 6) and reaction efficiencies of 91.0, 95.8, and 92.7%, respectively, for the mcyA, mcyE, and mcyG-based quantitative real-time PCR (qPCR) assays. The three assays successfully estimated potential microcystin-producing Microcystis genotypes from all field samples. The proportions of MicrocystismcyA, mcyE, and mcyG genotypes to total Microcystis cell counts showed substantial spatial variability ranging between 1.7-21.6%, 1.9-11.2%, and 2.2-22.6%, respectively. Correlation of microscopically determined total Microcystis counts to qPCR-based MicrocystismcyA, mcyE, or mcyG cell number equivalents resulted in highly significant associations with R(2) > 0.90. Thus, PCR-based assays targeting the mcyA, mcyG, and/or mcyE genes can serve as powerful screening tools for rapid and sensitive estimation of microcystin-producing Microcystis genotypes in freshwater water bodies.

Quantification and genetic diversity of total and microcystin-producing Microcystis during blooming season in Tai and Yang-cheng lakes, China

AIMS

The aims of present study were to evaluate the abundances, genetic diversity of total and microcystin-producing Microcystis over temporal and spatial scales, and to investigate relationships among Microcystis and water parameters in Tai and Yang-cheng lakes.

METHODS AND RESULTS

Abundances of total and microcystin-producing Microcystis varied across sampling periods and locations, which were assessed using qPCR with primers specific to Microcystis 16S rDNA and mcyA genes. The 16S rDNA from two lakes were relatively diverse. However, mcyA genes were rather conservative and were >97% identical to reference sequences. The highly positive correlations between mcyA and microcystin presence (r = 0·671 in Tai; r = 0·799 in Yang-cheng) suggested that mcyA can be used as a good biomarker for microcystin productions.

CONCLUSION

The results demonstrated that Microcystis were genetically diverse between these conjunctive lakes; however, mcyA genes were relatively conservative in two lakes. Quantifying mcyA by qPCR was an efficient tool for monitoring toxic Microcystis.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has improved our understanding of observable differences within and between each lake on spatial and temporal scales. And the discovery of new mcyA sequences in natural water enriched the understanding of phylogenetic diversity of Microcystis and toxin-production-related mcy gene.

Phylogeny of culturable cyanobacteria from Brazilian mangroves

The cyanobacterial community from Brazilian mangrove ecosystems was examined using a culture-dependent method. Fifty cyanobacterial strains were isolated from soil, water and periphytic samples collected from Cardoso Island and Bertioga mangroves using specific cyanobacterial culture media. Unicellular, homocytous and heterocytous morphotypes were recovered, representing five orders, seven families and eight genera (Synechococcus, Cyanobium, Cyanobacterium, Chlorogloea, Leptolyngbya, Phormidium, Nostoc and Microchaete). All of these novel mangrove strains had their 16S rRNA gene sequenced and BLAST analysis revealed sequence identities ranging from 92.5 to 99.7% when they were compared with other strains available in GenBank. The results showed a high variability of the 16S rRNA gene sequences among the genotypes that was not associated with the morphologies observed. Phylogenetic analyses showed several branches formed exclusively by some of these novel 16S rRNA gene sequences. BLAST and phylogeny analyses allowed for the identification of Nodosilinea and Oxynema strains, genera already known to exhibit poor morphological diacritic traits. In addition, several Nostoc and Leptolyngbya morphotypes of the mangrove strains may represent new generic entities, as they were distantly affiliated with true genera clades. The presence of non-ribosomal peptide synthetase, polyketide synthase, microcystin and saxitoxin genes were detected in 20.5%, 100%, 37.5% and 33.3%, respectively, of the 44 tested isolates. A total of 134 organic extracts obtained from 44 strains were tested against microorganisms, and 26% of the extracts showed some antimicrobial activity. This is the first polyphasic study of cultured cyanobacteria from Brazilian mangrove ecosystems using morphological, genetic and biological approaches.

Cyanotoxin occurrence and potentially toxin producing cyanobacteria in freshwaters of Greece: a multi-disciplinary approach

Cyanobacteria harmful algal blooms (or CyanoHABs) represent one of the most conspicuous waterborne microbial hazards in aquatic environments mostly due to the production of harmful secondary metabolites, known as cyanotoxins. In freshwaters of Greece only the presence of microcystins (MCs) has been reported despite the increasing occurrence of species able to produce other cyanotoxins too. In this paper, we studied the occurrence of potentially toxic cyanobacteria in water samples collected from six lakes and reservoirs in Greece. A multi-technique approach was applied by the use of microscopy, molecular, and immunological methods. Cyanobacteria were found in all the sites ranging from 4.7 × 10³ to 5.3 × 10⁸ individuals L⁻¹, representing >70% of the total phytoplankton abundance. Microcystins (MCs), cylindrospermopsins (CYNs), and saxitoxins (STXs) were detected using ELISA, in concentrations ranging from 3.9 to 108 μg L⁻¹, from 0.3 to 2.8 μg L⁻¹ and from 0.4 to 1.2 μg L⁻¹, respectively. In half of the samples examined more than one cyanotoxins were detected. Our results document the first report on the occurrence of CYN and STX in freshwaters of Greece and show that potential STX producers are Cylindrospermopsis raciborskii and Aphanizomenon flos-aquae. Further studies are needed to assess potential CYN producers. This study provides further data on the distribution and toxicity of C. raciborskii and Aph. flos-aquae and documents a C. raciborskii dominated bloom producing STX in Europe.

Monitoring approaches for a toxic cyanobacterial bloom

Cyanobacterial blooms, dominated by Microcystis sp. and associated microcystin variants, have been implicated in illnesses of humans and animals. Little is known regarding the formation of blooms and the presence of cyanotoxin variants in water bodies. Furthermore, the role played by ecological parameters, in regulating Microcystis blooms is complicate and diverse. Local authorities responsible for water management are often faced with the challenging task of dealing with cyanobacterial blooms. Therefore, the development of suitable monitoring approaches to characterize cyanobacterial blooms is an important goal. Currently, various biological, biochemical and physicochemical methods/approaches are being used to monitor cyanobacterial blooms and detect microcystins in freshwater bodies. Because these methods can vary as to the information they provide, no single approach seemed to be sufficient to accurately monitor blooms. For example, immunosensors are more suited for monitoring the presence of toxins in clear water bodies while molecular methods are more suited to detect potentially toxic strains. Thus, monitoring approaches should be tailored for specific water bodies using methods based on economic feasibility, speed, sensitivity and field applicability. This review critically evaluates monitoring approaches that are applicable to cyanobacterial blooms, especially those that focus on the presence of Microcystis, in freshwater bodies. Further, they were characterized and ranked according to their cost, speed, sensitivity and selectivity. Suggested improvements were offered as well as future research endeavors to accommodate anticipated environmental changes.

Hepatotoxic seafood poisoning (HSP) due to microcystins: a threat from the ocean?

Cyanobacterial blooms are a major and growing problem for freshwater ecosystems worldwide that increasingly concerns public health, with an average of 60% of blooms known to be toxic. The most studied cyanobacterial toxins belong to a family of cyclic heptapeptide hepatotoxins, called microcystins. The microcystins are stable hydrophilic cyclic heptapeptides with a potential to cause cell damage following cellular uptake via organic anion-transporting proteins (OATP). Their intracellular biologic effects presumably involve inhibition of catalytic subunits of protein phosphatases (PP1 and PP2A) and glutathione depletion. The microcystins produced by cyanobacteria pose a serious problem to human health, if they contaminate drinking water or food. These toxins are collectively responsible for human fatalities, as well as continued and widespread poisoning of wild and domestic animals. Although intoxications of aquatic organisms by microcystins have been widely documented for freshwater ecosystems, such poisonings in marine environments have only occasionally been reported. Moreover, these poisonings have been attributed to freshwater cyanobacterial species invading seas of lower salinity (e.g., the Baltic) or to the discharge of freshwater microcystins into the ocean. However, recent data suggest that microcystins are also being produced in the oceans by a number of cosmopolitan marine species, so that Hepatotoxic Seafood Poisoning (HSP) is increasingly recognized as a major health risk that follows consumption of contaminated seafood.

Harmful cyanobacterial blooms: causes, consequences, and controls

Cyanobacteria are the Earth's oldest oxygenic photoautotrophs and have had major impacts on shaping its biosphere. Their long evolutionary history (≈ 3.5 by) has enabled them to adapt to geochemical and climatic changes, and more recently anthropogenic modifications of aquatic environments, including nutrient over-enrichment (eutrophication), water diversions, withdrawals, and salinization. Many cyanobacterial genera exhibit optimal growth rates and bloom potentials at relatively high water temperatures; hence global warming plays a key role in their expansion and persistence. Bloom-forming cyanobacterial taxa can be harmful from environmental, organismal, and human health perspectives by outcompeting beneficial phytoplankton, depleting oxygen upon bloom senescence, and producing a variety of toxic secondary metabolites (e.g., cyanotoxins). How environmental factors impact cyanotoxin production is the subject of ongoing research, but nutrient (N, P and trace metals) supply rates, light, temperature, oxidative stressors, interactions with other biota (bacteria, viruses and animal grazers), and most likely, the combined effects of these factors are all involved. Accordingly, strategies aimed at controlling and mitigating harmful blooms have focused on manipulating these dynamic factors. The applicability and feasibility of various controls and management approaches is discussed for natural waters and drinking water supplies. Strategies based on physical, chemical, and biological manipulations of specific factors show promise; however, a key underlying approach that should be considered in almost all instances is nutrient (both N and P) input reductions; which have been shown to effectively reduce cyanobacterial biomass, and therefore limit health risks and frequencies of hypoxic events.

Quantification of toxigenic Microcystis spp. in freshwaters by quantitative real-time PCR based on the microcystin synthetase A gene

A method to estimate the abundance of toxigenic Microcystis in environmental samples by using quantitative real-time PCR was developed and optimized. The basis of this method is the amplification of a highly conserved region of the mcyA gene within the microcystin synthetase gene cluster. Using this method, the average copy number of mcyA gene per cell in toxigenic Microcystis strains was estimated. The molecular markers and method developed in this study can be used to monitor toxigenic strains of Microcystis in Korean freshwaters, in which harmful cyanobacterial blooms are routinely found.

Cyanophage infection in the bloom-forming cyanobacteria Microcystis aeruginosa in surface freshwater

Host-like genes are often found in viral genomes. To date, multiple host-like genes involved in photosynthesis and the pentose phosphate pathway have been found in phages of marine cyanobacteria Synechococcus and Prochlorococcus. These gene products are predicted to redirect host metabolism to deoxynucleotide biosynthesis for phage replication while maintaining photosynthesis. A cyanophage, Ma-LMM01, infecting the toxic cyanobacterium Microcystis aeruginosa, was isolated from a eutrophic freshwater lake and assigned as a member of a new lineage of the Myoviridae family. The genome encodes a host-like NblA. Cyanobacterial NblA is known to be involved in the degradation of the major light harvesting complex, the phycobilisomes. Ma-LMM01 nblA gene showed an early expression pattern and was highly transcribed during phage infection. We speculate that the co-option of nblA into Microcystis phages provides a significant fitness advantage to phages by preventing photoinhibition during infection and possibly represents an important part of the co-evolutionary interactions between cyanobacteria and their phages.