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In eutrophied marine systems such as the Baltic Sea, diazotrophic cyanobacteria have the potential to add additional bioavailable nitrogen (N) to the system through fixation of atmospheric dinitrogen (N2). However, their growth is regarded to be limited by phosphorus availability (P). This study investigates the response of two cyanobacteria species, Aphanizomenon flosaquae and Nodularia spumigena, collected from the Gulf of Riga under different environmental conditions to a short-period dissolved inorganic phosphorus (DIP) enrichment. The samples were collected during the summer cyanobacterial bloom of 2022 in the central region of the Gulf of Riga. Contrary to expectations, neither species demonstrated a significant increase in biomass. The study also established that N2-fixation rates did not correlate directly with the total diazotrophic cyanobacteria biomass, but showed a significant correlation with heterocyst presence in both species addressed during this study. The findings suggest the influence of additional factors beyond DIP availability on the N2-fixing cyanobacteria growth in the Gulf of Riga. [ABSTRACT FROM AUTHOR]

Evidence suggests that low cobalt (Co) may limit heterocyst frequency (HF) in filamentous diazotrophic cyanobacteria. Therefore, the effect of three Co concentrations on HF in four species in the genera Aphanizomenon and Dolichospermum was examined in N‐depleted (N was not added) culture. Long‐term HF data were also analysed in experimentally fertilised N‐limited Lake 227.HF ranges and means at 0.17, 17, and 170 nmol Co/L were 4.1%–5.7% (4.6%), 5.4%–7.4% (6.4%), and 5.9%–9.3% (7.4%), respectively, after 11 days of growth in batch cultures suggesting that Co plays a role in regulating HF. HF at 0.17 nmol/L was significantly different from HF at the two higher concentrations in all species implicating Co in heterocyst differentiation. However, growth rates and final biovolume yields were not significantly affected by Co in any of the species.Applying the ratio of total phosphorus (TP)/Co in culture media (106) at 0.17 nmol Co/L to an N‐limited system implies that dissolved Co would have to be less than 1 pmol/L to severely limit HF at 1 μmol TP/L. This Co concentration is much lower than dissolved Co in Lake 227 during an Aphanizomenon skujae bloom with 1 μmol TP/L in 2017. Furthermore, Co increased from 0.7 to 2.0 nmol/L simultaneously increasing with HF and cyanobacteria biomass suggesting that Co probably did not limit HF and bloom biomass in Lake 227.Mean summer HFs in Lake 227 during 2000–2020 were 3.4% (epilimnion) and 4.0% (metalimnion), similar to HF at the lowest Co in the cultures. However, HF was significantly higher after 2015 following a shift in dominant bloom species from A. schindlerii to the smaller A. skujae. Calculations suggest that the decrease in cell size may have prompted a higher HF in A. skujae in order to fix an amount of N per unit biomass similar to that fixed by the larger A. schindlerii. Thus, two previously unidentified factors, Co and cell size, can be added to the list of factors that affect HF. [ABSTRACT FROM AUTHOR]

Aphanizomenon flos-aquae (AFA) is the dominant filamentous cyanobacterium that develops into blooms in Upper Klamath Lake, Oregon, each year. During AFA bloom and collapse, ecosystem conditions for endangered Lost River and shortnose suckers deteriorate, thus motivating the need to identify processes that limit AFA abundance and decline. Here, we investigate the relations between AFA and other members of the microbial community (photosynthetic and nonphotosynthetic bacteria and archaea), how those relations impact abundance and collapse of AFA, and the types of microbial conditions that suppress AFA. We found significant spatial variation in AFA relative abundance during the 2016 bloom period using 16S rRNA sequencing. The Pelican Marina site had the lowest AFA relative abundance, and this was coincident with increased relative abundance of Candidatus Sericytochromatia, Flavobacterium , and Rheinheimera , some of which are known AFA antagonists. The AFA collapse coincided with phosphorus limitation relative to nitrogen and the increased relative abundance of Cyanobium and Candidatus Sericytochromatia, which outcompete AFA when dissolved inorganic nitrogen is available. The data collected in this study indicate the importance of dissolved inorganic nitrogen combined with microbial community structure in suppressing AFA abundance. [ABSTRACT FROM AUTHOR]

Twenty species/isolates of cyanobacteria and green algae were isolated from cyanobacterial bloom samples in lakes associated with the upper Qu'Appelle River drainage system in southern Saskatchewan, Canada. Three amoebae species (Cochliopodium sp., Vannella sp. and Vermamoeba vermiformis) were also isolated from one of these samples, and were subjected to grazing assays to determine which species of cyanobacteria or algae could potentially serve as a food source. Amoeba grazing rates were quantified based on the diameter of the plaque after 12 days on agar plate assays, and by estimation of the amoeba population growth rate from the rate of increase of plaque area. The common cyanobacterial bloom‐formers Dolichospermum sp. and Aphanizomenon flos‐aquae supported high growth rates for all three amoebae, while green algae, with the exception of one green alga/amoeba combination, did not support growth of the tested amoebae. Many of the cyanobacterial and algal isolates that did not support amoebae growth were ingested, suggesting that ingestion did not determine grazing success. Overall, while the cyanobacteria Dolichospermum sp. and Aphanizomenon flos‐aquae were suitable food sources for the amoebae, the other cyanobacteria were grazed in an unpredictable manner, with some species/strains grazed by some amoebae and some species not grazed at all. [ABSTRACT FROM AUTHOR]

Aphanizomenon sp. ULC602, recently isolated in a Belgian lake, is a filamentous, nitrogen-fixing, freshwater cyanobacterium that is one of the primary producers of cyanotoxins following its bloom formation, causing water contamination. This study aims to evaluate the effects of growing conditions and essential nutrients on the growth of Aphanizomenon sp. ULC602 via its production of chlorophyll-a (Chlo-a). Our results indicated that this bacterium could grow well at temperatures ranging from 18 to 25°C with an optimal pH of 6.0–7.5 under continuous lighting. It grew slowly in the absence of a carbon source or at lower carbon concentrations. The addition of nitrogen from nitrate and urea led to a less than 50% reduction of Chlo-a content compared to the medium lacking nitrogen. The iron bioavailability significantly stimulated the Chlo-a production, but it was saturated by an iron concentration of 0.115  mM. Moreover, a decrease in Chlo-a biomass was observed under sulfur deficiency. The bacterium could not grow well in media containing various phosphorus sources. In conclusion, as the growth and consequent forming bloom of cyanobacteria can be stimulated or inhibited by environmental conditions and eutrophication, our investigation could contribute to further studies to control the blooming of the target bacterium in freshwater. [ABSTRACT FROM AUTHOR]

Aphanizomenon is a genus of cyanobacteria that is filamentous and nitrogen-fixing and inhabits aquatic environments. This genus is known as one of the major producers of cyanotoxins that can affect water quality after the bloom period. In this study, an electrochemical aptasensor is demonstrated using a specific aptamer to detect Aphanizomenon sp. ULC602 for the rapid and sensitive detection of this bacterium. The principal operation of the generated aptasensor is based on the conformational change in the aptamer attached to the electrode surface in the presence of the target bacterium, resulting in a decrease in the current peak, which is measured by square-wave voltammetry (SWV). This aptasensor has a limit of detection (LOD) of OD750~0.3, with an extension to OD750~1.2 and a sensitivity of 456.8 μA·OD750−1·cm−2 without interference from other cyanobacteria. This is the first aptasensor studied that provides rapid detection to monitor the spread of this bacterium quickly in a targeted manner. [ABSTRACT FROM AUTHOR]

In this study, the effects of different doses of the mixed culture of Microcystis viridis and Aphanizomenon gracile, which are found intensively in some Şanlıurfa reservoirs, on maize (Zea mays L.) and lentil (Lens culinaris Medik) growth were investigated. The doses prepared from the cyanobacteria mixture were applied to the soils by spraying. In terms of root length, 2% dose in lentil and 1% dose in maize were 92% and 60% more effective respectively. The 2% application dose of the cyanobacteria mixture was 70% and 42% more effective respectively than the control in terms of plant height of both plants. In terms of green parts weights, 2% dose was found to be 164% and 30% more effective than the control in both maize and lentil. In root dry weight of maize and lentil, 2% dose was 680% and 139% more effective than the control in both plants. [ABSTRACT FROM AUTHOR]

The present study evaluated the ability of KlamExtra®, an Aphanizomenon flos aquae (AFA) extract, to counteract metabolic dysfunctions due to a high fat diet (HFD) or to accelerate their reversion induced by switching an HFD to a normocaloric diet in mice with diet-induced obesity. A group of HFD mice was fed with an HFD supplemented with AFA (HFD-AFA) and another one was fed with regular chow (standard diet—STD) alone or supplemented with AFA (STD-AFA). AFA was able to significantly reduce body weight, hypertriglyceridemia, liver fat accumulation and adipocyte size in HFD mice. AFA also reduced hyperglycaemia, insulinaemia, HOMA-IR and ameliorated the glucose tolerance and the insulin response of obese mice. Furthermore, in obese mice AFA normalised the gene and the protein expression of factors involved in lipid metabolism (FAS, PPAR-γ, SREBP-1c and FAT-P mRNA), inflammation (TNF-α and IL-6 mRNA, NFkB and IL-10 proteins) and oxidative stress (ROS levels and SOD activity). Interestingly, AFA accelerated the STD-induced reversion of glucose dysmetabolism, hepatic and VAT inflammation and oxidative stress. In conclusion, AFA supplementation prevents HFD-induced dysmetabolism and accelerates the STD-dependent recovery of glucose dysmetabolism by positively modulating oxidative stress, inflammation and the expression of the genes linked to lipid metabolism. [ABSTRACT FROM AUTHOR]

Introduction: Psychotic disorders affect approximately 0.75% of the general population worldwide with a great risk of complications and mortality. Clozapine and current antipsychotic drugs evoke serious complications. Aphanizomenon flosaquae (AFA) extract has antioxidant, anti-inflammatory and neuroprotective properties. Aim of Work: The aim of the work was to evaluate possible therapeutic effects of aphanizomenon flos-aquae extract in psychosis based on behavioral, biochemical and histopathological studies of CA1 region of the hippocampus. Materials and Methods: Sixty adult male albino rats were organized into five groups; control, AFA extract (200 mg/kg/d orally), psychosis (ketamine 25 mg/kg/d intraperitoneal), psychosis treated with clozapine (5 mg/kg/d intraperitoneal), psychosis treated with AFA extract. Ketamine was administered from day 1 to day 14. Clozapine and AFA extract were administered from day 8 to day 21. Behavioral tests including open field test (OFT), sucrose preference test (SPT) and novel object recognition test (NORT) besides biochemical analyses were conducted. After sacrification of rats, the brain was subjected to histological and immunohistochemical studies. Results: Ketamine induced positive, negative and cognitive symptoms of psychosis with increased brain acetylcholinesterase activity. Ketamine also induced degenerative changes in the hippocampus with increased glial fibrillary acidic protein (GFAP), P53 positive cells and decreased myelin basic protein (MBP) expression. Clozapine and AFA extract reversed the symptomatic and degenerative changes of psychosis, decreased brain acetylcholinesterase activity, decreased GFAP, P53 positive cells and increased MBP expression. However, clozapine promoted weight gain, dyslipidemia, hyperglycemia and agranulocytosis. Conclusion: AFA extract has therapeutic effects against ketamine induced psychosis without causing the side effects of clozapine. [ABSTRACT FROM AUTHOR]

Aphanizomenon sp. ULC602, recently isolated in a Belgian lake, is a filamentous, nitrogen-fixing, freshwater cyanobacterium that is one of the primary producers of cyanotoxins following its bloom formation, causing water contamination. This study aims to evaluate the effects of growing conditions and essential nutrients on the growth of Aphanizomenon sp. ULC602 via its production of chlorophyll-a (Chlo-a). Our results indicated that this bacterium could grow well at temperatures ranging from 18 to 25°C with an optimal pH of 6.0–7.5 under continuous lighting. It grew slowly in the absence of a carbon source or at lower carbon concentrations. The addition of nitrogen from nitrate and urea led to a less than 50% reduction of Chlo-a content compared to the medium lacking nitrogen. The iron bioavailability significantly stimulated the Chlo-a production, but it was saturated by an iron concentration of 0.115 mM. Moreover, a decrease in Chlo-a biomass was observed under sulfur deficiency. The bacterium could not grow well in media containing various phosphorus sources. In conclusion, as the growth and consequent forming bloom of cyanobacteria can be stimulated or inhibited by environmental conditions and eutrophication, our investigation could contribute to further studies to control the blooming of the target bacterium in freshwater.

Cyanobacteria harmful algal blooms (cyanoHABs) can have impacts on human health, aquatic ecosystems, and the economy. Nutrient management is an important mitigation and even remediation strategy. In this work, the paralytic shellfish toxin (PST)-producing Aphanizomenon (Aphan.) flos-aquae (Linnaeus) Ralfs ex Bornet & Flahault (now identified as Aphan. sp.) single filament isolate NH-5 was grown in P-depleted media, N-depleted media, and complete BG-11 media. Growth and heterocyst and vegetative cells were monitored using dry weight and cell counts. Ultrasonication was used to separate heterocysts from vegetative cells. HPLC-FLD with post-column derivatization was used to determine the saxitoxin (STX) and neosaxitoxin (NEOSTX) concentration per cell. Aphan. sp. NH-5 biomass was lower in the P-depleted media than in the N-depleted media and the control, though higher heterocyst counts were detected in the N-depleted media. The heterocyst toxin concentration was significantly higher compared to the vegetative cells for the N-depleted media, control, and P-depleted media. However, no significant differences were found among all preparations with regard to the STX-to-NEOSTX ratio. We conclude that N limitation induced higher heterocyst numbers and that N fixation activity is a factor behind the increase in the STX and NEOSTX production of Aphan. sp. NH-5. [ABSTRACT FROM AUTHOR]

To control harmful algae blooms (HABs), methods based on natural mechanisms are now required. We investigated the effects of an algicide derived from macrophyte metabolites, namely mixtures of gallic, tetradecanoic, heptanoic, and octanoic acids (1:1:1:1 mass ratio, a total concentration of 14 mg/L), on the biomass of cyanobacteria and other plankton and the production of microcystins under experimental conditions. Two types of microcosms have been created: simple (microalgae, cyanobacteria, and zooplankton) and complex (microalgae, cyanobacteria, zooplankton, and planktivorous fish). We observed the dynamics of the phytoplankton structure, the concentrations of microcystins and chlorophyll-a, hydrochemistry, and the status of zooplankton and fish in both types of microcosms with and without algicide for one month (from 19 July to 19 August 2021). The introduction of algicide caused changes in phytoplankton structure, a drop in cyanobacterial biomass, and a decrease in the total concentration of microcystins. Surprisingly, the contributions of the most toxic microcystins (LR form) were higher in both types of microcosms exposed to algicide than in microcosms without algicide. The inhibitory effect on the cyanobacterial biomass was most significant in complex ecosystems (containing fish), while it was only observed at the end of the exposure in simple ecosystems. Not only algicide but also phytoplankton consumed by fish and zooplankton, as well as nutrient excretory activity by both consumers, seem to have impact on cyanobacterial biomass. This study found that the using chemical substances similar to macrophyte metabolites can help regulate HABs and cyanotoxins. However, the results differ depending on ecosystem type. [ABSTRACT FROM AUTHOR]

Cyano-phycocyanin (C-PC) is a light-absorbing biliprotein found in cyanobacteria, commonly known as blue-green algae. Due to its antioxidative, anti-inflammatory, and anticancer properties, this protein is a promising substance in medicine and pharmaceuticals. However, cyanobacteria tend to bind heavy metals from the environment, making it necessary to ensure the safety of C-PC for the development of pharmaceutical products, with C-PC isolated from naturally collected cyanobacterial biomass. This study aimed to determine the content of the most toxic heavy metals, arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) in C-PC isolated from different cyanobacterial biomasses collected in the Kaunas Lagoon during 2019–2022, and compare them with the content of heavy metals in C-PC isolated from cultivated Spirulina platensis (S. platensis). Cyanobacteria of Aphanizomenon flos-aquae (A. flos-aquae) dominated the biomass collected in 2019, while the genus Microcystis dominated the biomasses collected in the years 2020 and 2022. Heavy metals were determined using inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS analysis revealed higher levels of the most investigated heavy metals (Pb, Cd, and As) in C-PC isolated from the biomass with the dominant Microcystis spp. compared to C-PC isolated from the biomass with the predominant A. flos-aquae. Meanwhile, C-PC isolated from cultivated S. platensis exhibited lower concentrations of As and Pb than C-PC isolated from naturally collected cyanobacterial biomass. [ABSTRACT FROM AUTHOR]

• An efficient and high-throughput tool for monitoring Aphanizomenon was established. • Aphanizomenon -specific primers were developed for eDNA metabarcoding. • The utility of eDNA metabarcoding for field-based monitoring was validated. • Aphanizomenon abundance in Beijing was region- and season-dependent. • Four environmental factors driving of Aphanizomenon abundance were identified. Harmful algal blooms (HABs) have emerged as a critical global environmental and ecological concern. Timely and accurate monitoring of the prevalent bloom-forming genera is crucial for HAB management. Conventional microscope-based methods are time-consuming, labor-intensive, and specialized expertise-dependent, often making them impractical for large-scale surveillance. Molecular methods, such as metabarcoding, provide efficient technical solutions; however, the lack of competent PCR primers and further field validation present obstacles to their wide use. Here, we successfully developed Aphanizomenon -specific primers and validated the application of environmental DNA (eDNA) metabarcoding for field-based monitoring of Aphanizomenon in 37 sites across lentic and lotic freshwater ecosystems in Beijing. The sensitivity and specificity tests of newly developed primers demonstrated high performance - comprehensive recovery of biodiversity in Aphanizomenon communities and high ratios (>95%) of Aphanizomenon sequences in datasets. We observed significant correlations between the sequence abundance derived from eDNA metabarcoding and the total cell density determined through microscopic identification across all the sampling sites, both in the spring (r = 0.8086, p < 0.0001) and summer (r = 0.7902, p < 0.0001), thus validating the utility of eDNA metabarcoding based on the newly developed primers for monitoring in the field. Further, we identified key environmental variables that were primary drivers responsible for the spatiotemporal distribution of Aphanizomenon abundance. These variables included temperature, total nitrogen, and dissolved oxygen in lentic ecosystems, and total phosphorus in lotic ecosystems. The method developed and validated here offers an accurate, efficient, and high-throughput tool for the monitoring of Aphanizomenon blooms in freshwater ecosystems. [Display omitted] [ABSTRACT FROM AUTHOR]

This study aimed to develop an empirical model to predict the spatial distribution of Aphanizomenon using the Ridiyagama reservoir in Sri Lanka with a dual-model strategy. In December 2020, a bloom was detected with a high density of Aphanizomenon and chlorophyll-a concentration. We generated a set of algorithms using in situ chlorophyll-a data with surface reflectance of Sentinel-2 bands on the same day using linear regression analysis. The in situ chlorophyll-a concentration was better regressed to the reflectance ratio of (1 + R665)/(1–R705) derived from B4 and B5 bands of Sentinel-2 with high reliability (R2 = 0.81, p < 0.001). The second regression model was developed to predict Aphanizomenon cell density using chlorophyll-a as the proxy and the relationship was strong and significant (R2 = 0.75, p

Obesity and related metabolic dysfunctions are associated with neurodegenerative diseases, such as Alzheimer's disease. Aphanizomenon flos-aquae (AFA) is a cyanobacterium considered a suitable supplement for its nutritional profile and beneficial properties. The potential neuroprotective effect of an AFA extract, commercialized as KlamExtra®, including the two AFA extracts Klamin® and AphaMax®, in High-Fat Diet (HFD)-fed mice was explored. Three groups of mice were provided with a standard diet (Lean), HFD or HFD supplemented with AFA extract (HFD + AFA) for 28 weeks. Metabolic parameters, brain insulin resistance, expression of apoptosis biomarkers, modulation of astrocytes and microglia activation markers, and Aβ deposition were analyzed and compared in the brains of different groups. AFA extract treatment attenuated HFD-induced neurodegeneration by reducing insulin resistance and loss of neurons. AFA supplementation improved the expression of synaptic proteins and reduced the HFD-induced astrocytes and microglia activation, and Aβ plaques accumulation. Together, these outcomes indicate that regular intake of AFA extract could benefit the metabolic and neuronal dysfunction caused by HFD, decreasing neuroinflammation and promoting Aβ plaques clearance. [ABSTRACT FROM AUTHOR]

Harmful cyanobacterial blooms are an increasing threat to water quality. The interactions between two ecophysiological functional traits of cyanobacteria, diazotrophy (nitrogen [N]‐fixation) and N‐rich cyanotoxin synthesis, have never been examined in a stoichiometric explicit manner. We explored how a gradient of resource N : phosphorus (P) affects the biomass, N, P stoichiometry, light‐harvesting pigments, and cylindrospermopsin production in a N‐fixing cyanobacterium, Aphanizomenon. Low N : P Aphanizomenon cultures produced the same biomass as populations grown in high N : P cultures. The biomass accumulation determined by carbon, indicated low N : P Aphanizomenon cultures did not have a N‐fixation growth trade‐off, in contrast to some other diazotrophs that maintain stoichiometric N homeostasis at the expense of growth. However, N‐fixing Aphanizomenon populations produced less particulate cylindrospermopsin and had undetectable dissolved cylindrospermopsin compared to non‐N‐fixing populations. The pattern of low to high cyanotoxin cell quotas across an N : P gradient in the diazotrophic cylindrospermopsin producer is similar to the cyanotoxin cell quota response in nondiazotrophic cyanobacteria. We suggest that diazotrophic cyanobacteria may be characterized into two broad functional groups, the N‐storage‐strategists and the growth‐strategists, which use N‐fixation differently and may determine patterns of bloom magnitude and toxin production in nature. [ABSTRACT FROM AUTHOR]

Aphanizomenon is a genus of cyanobacteria that is filamentous and nitrogen-fixing and inhabits aquatic environments. This genus is known as one of the major producers of cyanotoxins that can affect water quality after the bloom period. In this study, an electrochemical aptasensor is demonstrated using a specific aptamer to detect Aphanizomenon sp. ULC602 for the rapid and sensitive detection of this bacterium. The principal operation of the generated aptasensor is based on the conformational change in the aptamer attached to the electrode surface in the presence of the target bacterium, resulting in a decrease in the current peak, which is measured by square-wave voltammetry (SWV). This aptasensor has a limit of detection (LOD) of OD750~0.3, with an extension to OD750~1.2 and a sensitivity of 456.8 μA·OD750−1·cm−2 without interference from other cyanobacteria. This is the first aptasensor studied that provides rapid detection to monitor the spread of this bacterium quickly in a targeted manner.

The semi-enclosed Baltic Sea experiences regular summer blooms of diazotrophic cyanobacteria. Previously, it has been conclusively demonstrated that in open nitrogen-limited parts of the Baltic Sea, cyanobacteria successfully fix atmospheric N2. At the same time, diazotrophic activity is still poorly understood in Baltic Sea sub-regions where nitrogen and phosphorus are co-limiting primary production. To address this gap in research, we used the15 N tracer method for in situ incubations and measured the N2-fixation rate of heterocyst-forming cyanobacteria and picocyanobacteria in the Gulf of Riga, Baltic Sea, from April to September. Physicochemical variables and phytoplankton community composition were also determined. Our results show that the dominant species of cyanobacteria for this region (Aphanizomenon flosaquae) was present in the phytoplankton community during most of the study period. We also establish that the N2-fixation rate has a strong correlation with the proportion of A. flosaquae biomass containing heterocysts (r = 0.80). Our findings highlight the importance of a heterocyst-focused approach for an accurate diazotrophic activity evaluation that is one of the foundations for future management and protection of the Baltic Sea. [ABSTRACT FROM AUTHOR]

The cyanobacteria-associated microbiome is constantly reshaped by bloom development. However, the synergistic-antagonistic nature of the relationships between Microcystis and its microbiome still remains unclear. Therefore, temporal changes of bacterioplankton communities and their functional potential through different developing stages of a Microcystis toxigenic bloom were investigated, considering bacterioplankton assemblages as particle-attached (PAB) and free-living (FLB) bacteria. 16S rRNA sequencing revealed that PAB were represented by Proteobacteria and Cyanobacteria, while FLB by Proteobacteria and Actinobacteria. Network and ordination analyses indicated that PAB inter-relationships were more complex—numerous connections between taxa with stronger correlations, than FLB—rather influenced by physico-chemical parameters. PAB in pre-summer was diverse with Proteobacteria containing potential taxa involved in nitrogen-transforming processes. In mid-summer, PAB presented a mix-bloom dominated by Snowella, Aphanizomenon, and Microcystis, which were succeeded by toxigenic Microcystis in post-summer. Both periods were associated to potential taxa with parasitic/predatory lifestyles against cyanobacteria. In post-summer, Sutterellaceae were recognized as poor water quality indicators, and their strong association with Microcystis could have represented an increased threat for that period. Microcystis was a major factor significantly reducing PAB diversity and evenness, suggesting that it negatively influenced bacterioplankton assemblages, probably also altering the overall community functional potential. [ABSTRACT FROM AUTHOR]

Cyano-phycocyanin (C-PC) is a light-absorbing biliprotein found in cyanobacteria, commonly known as blue-green algae. Due to its antioxidative, anti-inflammatory, and anticancer properties, this protein is a promising substance in medicine and pharmaceuticals. However, cyanobacteria tend to bind heavy metals from the environment, making it necessary to ensure the safety of C-PC for the development of pharmaceutical products, with C-PC isolated from naturally collected cyanobacterial biomass. This study aimed to determine the content of the most toxic heavy metals, arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) in C-PC isolated from different cyanobacterial biomasses collected in the Kaunas Lagoon during 2019–2022, and compare them with the content of heavy metals in C-PC isolated from cultivated Spirulina platensis (S. platensis). Cyanobacteria of Aphanizomenon flos-aquae (A. flos-aquae) dominated the biomass collected in 2019, while the genus Microcystis dominated the biomasses collected in the years 2020 and 2022. Heavy metals were determined using inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS analysis revealed higher levels of the most investigated heavy metals (Pb, Cd, and As) in C-PC isolated from the biomass with the dominant Microcystis spp. compared to C-PC isolated from the biomass with the predominant A. flos-aquae. Meanwhile, C-PC isolated from cultivated S. platensis exhibited lower concentrations of As and Pb than C-PC isolated from naturally collected cyanobacterial biomass.

To control harmful algae blooms (HABs), methods based on natural mechanisms are now required. We investigated the effects of an algicide derived from macrophyte metabolites, namely mixtures of gallic, tetradecanoic, heptanoic, and octanoic acids (1:1:1:1 mass ratio, a total concentration of 14 mg/L), on the biomass of cyanobacteria and other plankton and the production of microcystins under experimental conditions. Two types of microcosms have been created: simple (microalgae, cyanobacteria, and zooplankton) and complex (microalgae, cyanobacteria, zooplankton, and planktivorous fish). We observed the dynamics of the phytoplankton structure, the concentrations of microcystins and chlorophyll-a, hydrochemistry, and the status of zooplankton and fish in both types of microcosms with and without algicide for one month (from 19 July to 19 August 2021). The introduction of algicide caused changes in phytoplankton structure, a drop in cyanobacterial biomass, and a decrease in the total concentration of microcystins. Surprisingly, the contributions of the most toxic microcystins (LR form) were higher in both types of microcosms exposed to algicide than in microcosms without algicide. The inhibitory effect on the cyanobacterial biomass was most significant in complex ecosystems (containing fish), while it was only observed at the end of the exposure in simple ecosystems. Not only algicide but also phytoplankton consumed by fish and zooplankton, as well as nutrient excretory activity by both consumers, seem to have impact on cyanobacterial biomass. This study found that the using chemical substances similar to macrophyte metabolites can help regulate HABs and cyanotoxins. However, the results differ depending on ecosystem type.

Aphanizomenon flos-aquae (A. flos-aquae) blooms are serious environmental and ecological problems. Extracellular polymeric substances (EPSs) are among the most important indicators for the growth and aggregation of A. flos-aquae. In this study, the secretion of the EPS matrix under temperature rise (7-37°C) was investigated and the role of this matrix in A. flos-aquae aggregation was quantified. First, when the temperature increased, the aggregation ratio increased from 41.85 to 91.04%. Meanwhile, we found that when soluble EPSs (S-EPSs), loosely bound EPSs (LB-EPSs), and tightly bound EPSs (TB-EPSs) were removed successively, the aggregation ratio decreased from 69.29 to 67.45%, 61.47%, and 41.14%, respectively. Second, the content of polysaccharides in the EPS matrix was higher than the content of proteins under temperature change. The polysaccharide in TB-EPSs was closely related to the aggregation ability of A. flos-aquae (P < 0.01). Third, PARAFAC analysis detected two humic-like substances and one protein-like substance in EPSs. Furthermore, Fourier transforms infrared spectroscopy (FTIR) showed that with increasing temperature, the polysaccharide-related functional groups increased, and the absolute value of the zeta potential decreased. In conclusion, these results indicated that a large number of polysaccharides in TB-EPSs were secreted under increasing temperature, and the polysaccharide-related functional groups increased correspondingly, which reduced the electrostatic repulsion between algal cells, leading to the destruction of the stability of the dispersion system, and then the occurrence of aggregation. This helps us to understand the process of filamentous cyanobacterial aggregation in lakes. [ABSTRACT FROM AUTHOR]

This study aimed to develop an empirical model to predict the spatial distribution of Aphanizomenon using the Ridiyagama reservoir in Sri Lanka with a dual-model strategy. In December 2020, a bloom was detected with a high density of Aphanizomenon and chlorophyll-a concentration. We generated a set of algorithms using in situ chlorophyll-a data with surface reflectance of Sentinel-2 bands on the same day using linear regression analysis. The in situ chlorophyll-a concentration was better regressed to the reflectance ratio of (1 + R665)/(1–R705) derived from B4 and B5 bands of Sentinel-2 with high reliability (R² = 0.81, p < 0.001). The second regression model was developed to predict Aphanizomenon cell density using chlorophyll-a as the proxy and the relationship was strong and significant (R² = 0.75, p<0.001). Coupling the former regression models, an empirical model was derived to predict Aphanizomenon cell density in the same reservoir with high reliability (R² = 0.71, p<0.001). Furthermore, the predicted and observed spatial distribution of Aphanizomenon was fairly agreed. Our results highlight that the present empirical model has a high capability for an accurate prediction of Aphanizomenon cell density and their spatial distribution in freshwaters, which helps in the management of toxic algal blooms and associated health impacts. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms have become a serious global environmental issue due to their potential risk for releasing detrimental secondary metabolites into aquatic ecosystems, posing a great threat to water quality management for public health authorities. Aphanizomenon, a common filamentous cyanobacterial genus belonging to Nostocales, is under particular concern because its several members are able to form harmful blooms. Furthermore, succession of bloom between A. flos-aquae and Microcystis occurs in many natural lakes. To evaluate the competitiveness of A. flos-aquae vs. M. aeruginosa, two sets of experiments at different ratios of biomass at 15 °C and 25 °C were conducted. Results show that at 15 °C, the two species were able to coexist, and A. flos-aquae showed a specific higher growth rate, and its growth was promoted by the presence of M. aeruginosa. At 25 °C, the growth of A. flos-aquae was inhibited by the biomass of M. aeruginosa, and M. aeruginosa suppressed A. flos-aquae in competition. Additionally, the vegetative cell size of A. flos-aquae was significantly influenced by the co-culture with M. aeruginosa, whereas the filament length of A. flos-aquae was not significantly affected. This study confirms that temperature is the dominating factor on the succession of A. flos-aquae and M. aeruginosa of a different biomass. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) are naturally occurring phenomena, and cyanobacteria are the most commonly occurring HABs in freshwater systems. Cyanobacteria HABs (cyanoHABs) negatively affect ecosystems and drinking water resources through the production of potent toxins. Furthermore, the frequency, duration, and distribution of cyanoHABs are increasing, and conditions that favor cyanobacteria growth are predicted to increase in the coming years. Current methods for mitigating cyanoHABs are generally short-lived and resource-intensive, and have negative impacts on non-target species. Cyanophages (viruses that specifically target cyanobacteria) have the potential to provide a highly specific control strategy with minimal impacts on non-target species and propagation in the environment. A detailed review (primarily up to 2020) of cyanophage lifecycle, diversity, and factors influencing infectivity is provided in this paper, along with a discussion of cyanophage and host cyanobacteria relationships for seven prominent cyanoHAB-forming genera in North America, including: Synechococcus, Microcystis, Dolichospermum, Aphanizomenon, Cylindrospermopsis, Planktothrix, and Lyngbya. Lastly, factors affecting the potential application of cyanophages as a cyanoHAB control strategy are discussed, including efficacy considerations, optimization, and scalability for large-scale applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modified clay (MC) is first applied for the mitigation of Aphanizomenon flos-aquae. • The settling kinetics of MC in mitigating HABs are investigated. • The mitigation of HABs using MC will be accelerated by hydraulic regulation. • Large, compact, and rapidly settling flocs are prone to form under hydraulic shear. • The kinetic mechanism of HABs removal by MC based on flow field is revealed. Modified clay is considered to be the most direct and effective method for emergency mitigation of harmful algal blooms (HABs), and it has been widely applied. However, its application on Aphanizomenon flos-aquae blooms has not been reported. Additionally, the hydraulic characteristics of modified clay in settling algal cells and the mechanism of its influence by flow fields have not been well studied, which is detrimental to the effective application of modified clay in alleviating HABs. Therefore, this study investigates the feasibility of using modified clay to alleviate Aphanizomenon flos-aquae blooms through laboratory-scale experiments and field engineering applications, and analyzes the keinetic mechanism of algal cell settling by modified clay based on flow field characteristics. The results indicate that PAC-modified clay can effectively alleviate Aphanizomenon flos-aquae blooms, achieving a removal efficiency of over 90 %. Differences in mineral composition, particle size, mineral-to-PAC ratio, and hydraulic shear significantly affect the removal performance of algal cells. The flow field characteristics of the water not only affect the removal efficiency of algal cells, but also influence the settling speed of the cells. By artificially increasing hydraulic shear and enhancing the distribution of velocity and turbulence kinetic energy in the water, the interaction between algal cell-coagulant-clay particle is promoted, resulting in the formation of larger and denser flocs, yielding faster settling performance. In the practical engineering application at Changshuiyan Reservoir, the use of boat propellers to agitate the water also verified this reinforcing effect. Aphanizomenon flos-aquae blooms were effectively alleviated, and transparency increased from the initial 0.5 m to 5.5 m. This study, for the first time, combines flow field simulation of clay particle settling to analyze the kinetic mechanism of hydraulic shear in enhancing the efficiency of modified clay in alleviating HABs from a kinetic perspective. [ABSTRACT FROM AUTHOR]

Elevated geosmin concentrations in drinking water reservoirs can lead to customer complaints and increased treatment costs for utilities. Use of molecular approaches, like qPCR and targeted amplicon sequencing, can help with prediction and preventive measures, but many of the primers targeting the geosmin synthase gene suffer from limited coverage of taxa or poor specificity. Here, a set of primers (CGeo1F/R) were developed that had high specificity for geosmin synthase in cyanobacteria without the use of probes. When tested on samples from three drinking water reservoirs with elevated geosmin levels, these primers amplified the geosmin synthase gene in seven cyanobacterial genera, including Dolichospermum, Aphanizomenon, Cylindrospermum, Planktothrix, Nostoc, Coelosphaerium, and Tychonema. These primers exhibited acceptable amplification efficiency (∼ 90 %) and a linear amplification range of 6 × 101–6 × 105 copies per ml in lake water. Within the limited set of samples used to evaluate these primers, a good correlation was observed (r = 0.8) between abundance of geosmin synthase and geosmin concentration. When compared to some existing, well-utilized primers in the literature, these new primers had better specificity and amplification properties, and thus may prove valuable to other researchers. • Primers (Cgeo1) targeting geosmin synthase in cyanobacteria were developed. • Cgeo1 primers were specific to cyanobacteria and included seven genera in samples. • Cgeo1 primers outperformed two existing primers in efficiency and dynamic range. • Strong correlation observed (r = 0.8) between geosmin level and gene copy number. [ABSTRACT FROM AUTHOR]

Microbial esterases are a highly desirable tool for numerous biosynthetic and biotechnological applications requiring ester bond cleavage. Once identified, microbial esterases are often produced recombinantly in Escherichia coli to enhance yield and ease of purification. In this study a polyhistidine-tagged SGNH esterase gene (AaSGNH1), originating from the cyanobacterium Aphanizomenon flos-aquae, was cloned into an over-expression plasmid and expressed in BL21(DE3) cells. The recombinant esterase enzyme was produced as inactive inclusion bodies which were insoluble in 8 M urea but readily solubilized by the detergent Empigen BB®. Crucially, the procurement of active enzyme required controlled removal of detergent during column chromatography and dialysis steps. The refolded esterase was characterized with respect to its ability to catalyze the cleavage of p-nitrophenol esters of different chain lengths (C2, C8, C16). In addition, the temperature and pH optima were determined and it was found that the enzyme was most active at low temperatures (5–15 °C) and under alkaline conditions (pH 8–10). It was found that the kinetic properties of AaSGNH1 were remarkably similar to other SGNH esterases described thereby validating that the protein was effectively refolded. Overall, this study provides a simple strategy for isolating cold-active recombinant esterase enzyme when expressed as inclusion bodies. [ABSTRACT FROM AUTHOR]

Haig HA, Chegoonian AM, Davies J-M, Bateson D, Leavitt PR. 2021. Marked blue discoloration of late winter ice and water due to autumn blooms of cyanobacteria. Lake Reserv Manage. 38:1–15. Continued eutrophication of inland waters by nutrient pollution can combine with unprecedented atmospheric and lake warming to create emergent environmental surprises. Here we report the first known occurrence of marked blue discoloration of ice and water in highly eutrophic prairie lakes during late winter 2021. Intense blue staining was reported first to governmental agencies by ice fishers in early March 2021, then communicated widely through social media, resulting in First Nations and public concern over potential septic field release, toxic spills, urban pollution, and agricultural mismanagement. Analysis of water from stained and reference sites using ultraviolet (UV)–visible spectrophotometry and high-performance liquid chromatography demonstrated that the blue color arose from high concentrations (∼14 mg/L) of the cyanobacterial pigment C-phycocyanin that was released after an unexpected bloom of Aphanizomenon flos-aquae in late October 2020 was frozen into littoral ice. Remote sensing using the Sentinel 3 A/B OLCI and Sentinel 2 A/B MSI satellite platforms suggested that blue staining encompassed 0.68 ± 0.24 km2 (4.25 ± 1.5% of lake surface area), persisted over 4 weeks, and was located within 50 m of the lakeshore in regions where fall blooms of cyanobacteria had been particularly dense. Although toxin levels were low (∼0.2 μg microcystin/L), high concentrations of C-phycocyanin raised public concern over eutrophication, pollution, and climate change, and resulted in rapid governmental and academic response. Given that climate change and nutrient pollution are increasing the magnitude and duration of cyanobacterial blooms, blue staining of lake ice may become widespread in eutrophic lakes subject to ice cover. [ABSTRACT FROM AUTHOR]

Copyright of Environmental Science & Technology (10036504) is the property of Editorial Board of Environmental Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, titanium dioxide (TiO2) nano-fluid was blended with aphanizomenon Flos (AF) biodiesel blend in order to investigate the emission behaviour of compression ignition engine. Three different percentages of titanium dioxide (TiO2) nano-fluid was blended with aphanizomenon Flos (AF) biodiesel (20%) – diesel (80%) blend. Taguchi method was used to find the optimum level of titanium dioxide nanofluid. ANOVA was used to find the contribution of factors on the exhaust emission. As TiO2 content increases in AFD - TiO2 blend, NO emission of the engine increases. Correlation among the significant factors on the response was done using multiple linear regression equation. [ABSTRACT FROM AUTHOR]

In this study, the effects of different doses of mixed cultures of Microcystis viridis and Aphanizomenon gracile, which are densely found in some Şanlıurfa Dam Lakes, were investigated to determine their effects on the growth of vetch (Vicia sativa L.), chickpea (Cicer arietinum L.), and barley (Hordeum vulgare L.). The doses prepared from the cyanobacteria mixture were applied to the soil by spraying. In terms of root length, 1.5% application dose in vetch and 2% dose in chickpea and barley were found to be effective. The 2% application dose of the cyanobacteria mixture increased the plant height of all three plants compared to the control. While 2% application dose was found to be effective on root dry and wet weight in chickpea and barley, 1.5% application dose was found to be effective on shoot weight in vetch and chickpea. [ABSTRACT FROM AUTHOR]

In order to understand the community structure of phytoplankton and its relationship with environmental factors in Taihu National Wetland Park in northeast China, a study was conducted in Taihu in September 2020. The results showed that there were 39 species of phytoplankton belonging to 27 genera and 6 phyla, among which Chlorophyta was the most abundant (20 species). The abundance and biomass of 5# and 6# sampling sites were significantly higher than other sampling sites, which may be caused by eutrophication. In Taihu National Wetland Park, the dominant species were Merismopedia minima, Aphanizomenon flosaquae, Synedra acus, Synura.sp and Scenedesmus quadricauda. Phytoplankton community structure in autumn in Taihu National Wetland Park were mainly influenced by pH, NO3 - -N, and water temperature. This research can provide a scientific basis for biodiversity protection and pollution control in Taihu National Wetland Park. [ABSTRACT FROM AUTHOR]

Mozingo Lake, a reservoir in the mid-continental United States, was sampled 63 times between January 1999 and October 2015. Prior to 2005, phytoplankton biovolume was largely composed of Cryptomonas and cyanobacteria (mostly Aphanizomenon); these taxa correlated with the abundance of Daphnia and juvenile copepods, and were also influenced by competition between cyanobacteria and bacillariophytes. These relationships suggest the zooplankton community was primarily controlled by bottom-up processes during this time. In 2005, gizzard shad (Dorosoma cepedianum) first appeared in the lake, coinciding with the first spined and helmeted forms of Daphnia as well as their decline from 39% to 3% of zooplankton; the relative abundance of juvenile copepods increased concurrently. By 2007 phytoplankton biovolume had decreased by 88%. Although all phytoplankton phyla declined in absolute abundance, some were more heavily impacted. The relative abundance of Aphanizomenon declined from 50% to 6% of the phytoplankton biovolume; Cryptomonas remained common, but bacillariophytes became codominant. Despite the steep decline in phytoplankton biovolume, several important trophic interactions did not change: phytoplankton biovolume continued to control juvenile copepods, and competition continued between cyanobacteria and bacillariophytes. Although juvenile copepods continued to compete with Daphnia, the scarcity of the latter allowed a relative expansion of juvenile copepods and bacillariophytes. Because very few of the standard parameters correlated with phytoplankton, it seems likely that most of the changes were caused by the introduction of gizzard shad, which is an intense consumer of cyanobacteria and Daphnia. Gizzard shad likely initiated a trophic cascade both directly (through consumption) and indirectly (by shifting competition). Although other factors may have played a role, it seems clear that the introduction of gizzard shad can cause dramatic changes in both the zooplankton and phytoplankton communities by altering species relationships in top-down, bottom-up, as well as lateral control processes. [ABSTRACT FROM AUTHOR]

Great interest has been placed on studying algicidal bacteria to control cyanobacterial outbreaks in freshwater ecosystems. However, the mechanism of changes at the molecular and cellular level in cyanobacteria stressed by algicidal bacteria requires better exploration. Here, the physiological stress of Microcystis aeruginosa and Aphanizomenon gracile strains, two well-known bloom-forming cyanobacteria, was described when exposed to algicidal bacteria Morganella morganii SU7S0818 and Bacillus pumilus SU8S0818 (isolated from a eutrophic reservoir). The results indicated that both bacteria induced a strong algicidal activity, although Aphanizonmenon strains were more sensitive than Microcystis. Studied cyanobacterial strains accumulated high amounts of reactive oxygen species (ROS) contributing to almost complete cell death after six days of co-culture. Gene expression analysis based on the upregulation of the psb A and rec A genes for photosynthesis and DNA repair mechanisms, respectively, showed that A. gracile strains responded slower to cellular stress (24–30 h) than M. aeruginosa strains (12 h). Microscopic analyses revealed the increase of cyanophycin granules in affected cyanobacterial cells, which may indicate the development of a survival mechanism under algicidal stress conditions. These findings are critical to understanding and managing the problem of global expansion of harmful algal blooms caused by different species of cyanobacteria. [Display omitted] • Bacillus pumilus SU8S0818 and Morganella morganii SU7S0818 disrupt cyanobacteria. • Aphanizomenon gracile was more sensitive than Microcystis aeruginosa. • Photosynthesis and DNA damage/repair stress signal was slower for A. gracile. • Cyanobacterial ultrastructure cell damage was associated to ROS accumulation. • Cyanophicyn granules in damaged cells was regarded as a survival mechanism. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms pose a global environmental concern, with various genera contributing to their formation. The harmfulness of cyanobacterial blooms varies depending on the specific genus, yet the factors triggering their formation remain incompletely understood. This study conducted qPCR of sediment DNA in Lake Erhai to reconstruct the historical succession of three common bloom-forming cyanobacterial genera (i.e., Microcystis , Dolichospermum , and Aphanizomenon). The driving factors and their corresponding thresholds were identified, and human activities related to driving factors were evaluated. The results revealed two successions in the past century. The first succession transitioned from Aphanizomenon (1902–1978) to Microcystis and Dolichospermum (1978–1999), driven by TN:TP and TP. The second succession shifted from Microcystis and Dolichospermum (1978–1999) to Microcystis (1999–2010), driven by TP, TN:TP, and temperature. The thresholds of TP and TN:TP for the Microcystis bloom were 0.023 mg/L and 17, respectively. TN:TP was significantly influenced by domestic pollution and crop farming in both successions, while TP was significantly impacted by domestic pollution in the first succession and by pollution from crop and dairy farming in the second succession. These results shed light on the underlying mechanism responsible for the blooms of various cyanobacterial genera and could serve as a valuable reference for effectively preventing and controlling nutrient input in the watershed. [Display omitted] • Reconstruct centurial succession of bloom-forming cyanobacterial genera by qPCR. • Cyanobacterial genera succession was driven by TP, TN:TP, temperature. • Microcystis may be dominant when TP exceeds 0.023 mg/L and TN:TP exceeds 17. • Main human activities leading to the changes in TP and TN:TP were identified. [ABSTRACT FROM AUTHOR]

Dense blooms of diazotrophic filamentous cyanobacteria are formed every summer in the Baltic Sea. We estimated their contribution to nitrogen fixation by combining two decades of cyanobacterial biovolume monitoring data with recently measured genera-specific nitrogen fixation rates. In the Bothnian Sea, estimated nitrogen fixation rates were 80 kt N year−1, which has doubled during recent decades and now exceeds external loading from rivers and atmospheric deposition of 69 kt year−1. The estimated contribution to the Baltic Proper was 399 kt N year−1, which agrees well with previous estimates using other approaches and is greater than the external input of 374 kt N year−1. Our approach can potentially be applied to continuously estimate nitrogen loads via nitrogen fixation. Those estimates are crucial for ecosystem adaptive management since internal nitrogen loading may counteract the positive effects of decreased external nutrient loading. [ABSTRACT FROM AUTHOR]

Cyanobacteria may limit recreational use of waters and have negative impacts on ecosystem services. The aim of this study was to determine phosphorus (P) thresholds for cyanobacterial taxa, which form toxin-producing blooms (mass occurrences) in boreal lakes. These thresholds help to set robust P reduction targets for restoration measures. We used long-term (> 40 years) June–August data from > 2000 Finnish lakes to evaluate the total P (TP) thresholds for the most important bloom-forming cyanobacterial genera and selected Microcystis and Dolichospermum species. The analyses were carried out separately for oligohumic, mesohumic and polyhumic lakes. TP threshold values varied between 10 and 61 µg l−1. The values were lower in oligohumic (water colour < 30 mg Pt l−1) than mesohumic (water colour 30–90 mg Pt l−1) lakes. The highest TP threshold (50 µg l−1) was observed for Microcystis in polyhumic lakes, and the lowest (10 µg l−1) for Planktothrix in oligohumic lakes. [ABSTRACT FROM AUTHOR]

Viruses can significantly influence cyanobacteria population dynamics and activity, and through this the biogeochemical cycling of major nutrients. However, surprisingly little attention has been given to understand how viral infections alter the ability of diazotrophic cyanobacteria for atmospheric nitrogen fixation and its release to the environment. This study addressed the importance of cyanophages for net 15N2 assimilation rate, expression of nitrogenase reductase gene (nifH) and changes in nitrogen enrichment (15N/14N) in the diazotrophic cyanobacterium Aphanizomenon flos-aquae during infection by the cyanophage vB_AphaS-CL131. We found that while the growth of A. flos-aquae was inhibited by cyanophage addition (decreased from 0.02 h–1 to 0.002 h–1), there were no significant differences in nitrogen fixation rates (control: 22.7 × 10–7 nmol N heterocyte–1; infected: 23.9 × 10–7 nmol N heterocyte–1) and nifH expression level (control: 0.6–1.6 transcripts heterocyte–1; infected: 0.7–1.1 transcripts heterocyte–1) between the infected and control A. flos-aquae cultures. This implies that cyanophage genome replication and progeny production within the vegetative cells does not interfere with the N2 fixation reactions in the heterocytes of these cyanobacteria. However, higher 15N enrichment at the poles of heterocytes of the infected A. flos-aquae , revealed by NanoSIMS analysis indicates the accumulation of fixed nitrogen in response to cyanophage addition. This suggests reduced nitrogen transport to vegetative cells and the alterations in the flow of fixed nitrogen within the filaments. In addition, we found that cyanophage lysis resulted in a substantial release of ammonium into culture medium. Cyanophage infection seems to substantially redirect N flow from cyanobacterial biomass to the production of N storage compounds and N release. [ABSTRACT FROM AUTHOR]

This study describes the first report on saxitoxins (STXs) and anatoxin-a (ANTX-a) production by cyanobacteria in Lithuanian lakes. Seasonal fluctuation patterns for neurotoxins were determined in samples collected from eutrophic lakes during July–September. Strains of Aphanizomenon gracile, A. flos-aquae, Cuspidothrix issatschenkoi, Sphaerospermopsis aphanizomenoides and Anabaenopsis cf. elenkinii were also isolated from the lakes and screened for the occurrence of neurotoxic STXs, ANTX-a and for the cytotoxin cylindrospermopsin (CYN). The highest concentration of STX (up to 1.06 µg l–1 in Lake Jieznas) was detected during July‒August and coincided with a predominance of A. gracile in the phytoplankton. Of the isolated strains, only A. gracile was confirmed to be a producer of STXs by chemical (LC-MS/MS) and genetic (sxtA) methods. Sequencing of the phycocyanin intergenic spacer and flanking regions (cpcBA) revealed that A. gracile formed a genetically homogenous group. Only trace amounts of ANTX-a were detected in field samples (up to 0.31 µg l–1 in Lake Širvys). CYN was detected in neither the bloom samples nor in the isolated strains. [ABSTRACT FROM AUTHOR]

Copyright of Egyptian Journal of Experimental Biology (Botany) is the property of Egyptian Society of Experimental Biology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: The N2-fixing cyanobacterium, Aphanizomenon flos-aquae is a globally distributed bloom causing species that degrades water quality of fresh and marine water bodies. Overcoming phosphorus (P) deficiency is one of the ecological advantages for bloom-forming cyanobacteria. It remains unclear to what extent can A. flos-aquae alleviate P deficiency by regulating P using strategies. Results: Based on in situ observations of extracellular alkaline phosphatase (APase) in A. flos-aquae via enzyme-labeled fluorescence in freshwater bodies in China, Poland and Czechia, we further investigated responses of isolated A. flos-aquae to different P supplies (dissolved inorganic P (Pi) as +DIP, dissolved organic α-glycerophosphate and β-glycerophosphate as +DOPα and +DOPβ, P-free condition as P-depleted). The significantly negative relationships between percentage of APase producing cells and soluble reactive P concentration in both fields and cultures suggested that the excretion of APase in cyanobacterium was regulated by ambient Pi supply. Suffering from P deficiency in the P-depleted treatments, A. flos-aquae showed the highest APase activity but a vigorous growth at the early culture stage, which might also benefit from the formation of polyphosphate body (PPB) and the decrease of cell P quota. In the +DOP treatments, the coordination of dissolved DOP mineralization and continuous prompt utilization of PPB might contribute to a maintenance but not reproduction of A. flos-aquae when relying on DOP, since the specific growth rate kept around 0 cells L−1 day−1 at the second half culture period and the highest cell density reached only 13.38% of that in +DIP treatments while photochemical efficiency was comparable during the whole experiment. Luxury uptake of phosphate as PPB in the +DIP treatments was consistent to the canonical view of polyphosphate as P storage. Conclusion: Aphanizomenon flos-aquae could achieve an instantaneous growth in response to P deficiency with the coordination of P utilization strategies, while it maintained a long-term sustainable growth but not reproduction under sole DOP supply. Persistent and active reproduction could only be achieved in high Pi supply, which implying that an effective consequence can be expected for combating the bloom of A. flos-aquae when controlling P supply. [ABSTRACT FROM AUTHOR]

Eldridge SLC, Wood TM. 2019. Annual variation in microcystin occurrence in Upper Klamath Lake, Oregon, based on high-throughput DNA sequencing, qPCR, and environmental parameters. Lake Reserv Manage. 36:31–44. Cyanobacteria-dominated blooms in Upper Klamath Lake, Oregon, create poor water quality and produce microcystins that may be detrimental to local wildlife and human health. Genetic tools, including high-throughput DNA sequencing and quantitative polymerase chain reaction (qPCR), have been shown to improve the identification and quantification of key groups associated with these blooms over more traditional techniques. We examined the seasonal and interannual variations in nutrient (nitrogen and phosphorus) concentrations between 2013 and 2014 to describe the relations between these factors and the growth dynamics of Aphanizomenon and toxigenic Microcystis as described by DNA sequencing and qPCR. Although total nutrients and chlorophyll a concentrations were similar between years, qPCR results showed the cyanobacterial populations to be 40 times larger in 2014 and indicated a large shift from an Aphanizomenon-dominant, low microcystin-level regime in 2013 to one dominated later in the season by microcystin-producing Microcystis in 2014. In both years, the transition from Aphanizomenon to Microcystis was coincident with a late-season increase in nitrite-plus-nitrate concentrations and in dissolved inorganic nitrogen to dissolved inorganic phosphorus (DIN:DIP) ratios. However, these increases did not explain the large interannual differences in total cyanobacteria abundance. Rather, we hypothesized that year-to-year differences in bioavailable phosphorus, which also manifested as lower total nitrogen to total phosphorus (TN:TP) ratios, were responsible. [ABSTRACT FROM AUTHOR]

Photoreduction characteristics of divalent inorganic mercury (Hg2+) in the presence of specific algae species are still not well known. Laboratory experiments were conducted in the present study to identify the effects of different concentrations of living/dead algae species, including Aphanizomenon flosaquae (AF) and Microcystis aeruginosa (MA), on the photoreduction rate of Hg2+ under various light conditions. The experimental results showed that percentage reduction of Hg2+ was significantly influenced by radiation wavelengths, and dramatically decreased with the presence of algae. The highest percentage reduction of Hg2+ was induced by UV-A, followed by UV-B, visible light and dark for both living and dead AF , and the order was dark > UV-A > UV-B > visible light for both living and dead MA. There were two aspects, i.e., energy and attenuation rate of light radiation and excrementitious generated from algae metabolisms, were involved in the processes of Hg2+ photoreduction with the presence of algae under different light conditions. The percentage reduction of Hg2+ decreased from 15% to 11% when living and dead AF concentrations increased by 10 times (from 106 to 105 cells/mL), and decreased from 11% to ~ 9% in the case of living and dead MA increased. Algae can adsorb Hg2+ and decrease the concentration of free Hg2+, thus inhibiting Hg2+ photoreduction, especially under the conditions with high concentrations of algae. No significant differences were found in percentage reduction of Hg2+ between living and dead treatments of algae species. The results are of great importance for understanding the role of algae in Hg2+ photoreduction. Unlabelled Image [ABSTRACT FROM AUTHOR]

Coagulation-filtration hybrid process has been widely used in algae removal treatment to improve the water quality and alleviate the membrane fouling. However, the intricate interplay of how floc structure induced by coagulation hydraulic shear influences the cake layer and filtration performance in coagulation macro-filtration of microalgae remains unexplored. In this study, a novel coagulation filtration with macro-pore of 75 μm was first adopted for the rapid removal of Aphanizomenon flos-aquae , and the floc structure was artificially manipulated through various velocity gradients to explore the effect mechanism of the coagulation hydrodynamic shear on the macro-filtration performance from the perspectives of floc characteristics (size and fractal dimension) and cake layer structure (thickness and roughness). The results showed that an optimal average flux of 31257.64 ± 2776.28 L·m−2·h−1 can be achieved at a manipulated appropriate velocity gradient (19 s−1), which is 1.1–2.3 times the flux achieved at higher or non-velocity gradients. The flocs formed at low velocity gradient were large and loose, while those formed at high velocity gradient were small and compact. Subsequently, the cake layer stacked by loose flocs was thicker and coarser than that by compact flocs, and exhibited a lower specific cake resistance, yielding a higher average flux. Moreover, a theoretical model for average flux was developed by introducing the velocity gradient, which directly elucidates how hydrodynamic shear affects floc characteristic, cake structure and filtration flux for the coagulation macro-filtration of Aphanizomenon flos-aquae. This study lays a theoretical foundation for the optimization of coagulation macro-filtration performance of microalgae and provides a new solution for the large flux removal of cyanobacteria by artificially regulating the coagulation hydrodynamic shear. [Display omitted] [ABSTRACT FROM AUTHOR]

• An algal species identification algorithm based on R rs was developed. • The spatio-temporal distribution of the dominant algae in Lake Taihu was obtained. • The relationship between dominant algae and environmental factors were discussed. The proliferation of algal blooms can lead to environmental issues. The phytoplankton responsible for these blooms are diverse. Different species of bloom-forming algae have distinct characteristics and hazards, and therefore need different treatment methods. An accurate and quick determination of the spatial and temporal distribution characteristics of different algal species is crucial for lake ecological restoration. Based on the differences in remote sensing reflectance (R rs) of various typical algae species in eutrophic lakes (including Microcystis aeruginosa , Aphanizomenon sp., and Pseudanabaena sp. in Cyanobacteria and Chlorella sp. and Scenedesmus quadricauda in Chlorophytes), difference index and algae distinguishing index were developed to differentiate algae species. A validation, using an independent dataset from an indoor experiment and in-situ-measured and satellite-image-derived R rs , showed that the algorithm can provide reliable results (overall accuracies of 81.97%, 81.25%, and 60.42%, respectively). According to Ocean and Land Color Instrument images of Lake Taihu in the period of 2016 to 2020, Microcystis was the dominant algae, followed by Pseudanabaena and Aphanizomenon. The dominance of the two types of Chlorophytes was less pronounced. The proportion of Microcystis as the dominant algae was highest in summer, while the proportion of Pseudanabaena peaked in winter. The proportion of Aphanizomenon varied slightly throughout the year, while the proportion of the two Chlorophytes peaked in winter. In terms of spatial distribution, the patterns in spring and autumn were relatively similar. In summer, approximately 80% of the lake was dominated by Microcystis. In winter, Chlorella and Scenedesmus were more prevalent along the southeastern shore of Lake Taihu. The construction and application of this model can provide a technical support for prediction and prevention of blooms in inland lakes. [ABSTRACT FROM AUTHOR]

Sedimentary ancient DNA-based studies have been used to probe centuries of climate and environmental changes and how they affected cyanobacterial assemblages in temperate lakes. Due to cyanobacteria containing potential bloom-forming and toxin-producing taxa, their approximate reconstruction from sediments is crucial, especially in lakes lacking long-term monitoring data. To extend the resolution of sediment record interpretation, we used high-throughput sequencing, amplicon sequence variant (ASV) analysis, and quantitative PCR to compare pelagic cyanobacterial composition to that in sediment traps (collected monthly) and surface sediments in Lake Tiefer See. Cyanobacterial composition, species richness, and evenness was not significantly different among the pelagic depths, sediment traps and surface sediments (p > 0.05), indicating that the cyanobacteria in the sediments reflected the cyanobacterial assemblage in the water column. However, total cyanobacterial abundances (qPCR) decreased from the metalimnion down the water column. The aggregate-forming (Aphanizomenon) and colony-forming taxa (Snowella) showed pronounced sedimentation. In contrast, Planktothrix was only very poorly represented in sediment traps (meta- and hypolimnion) and surface sediments, despite its highest relative abundance at the thermocline (10 m water depth) during periods of lake stratification (May–October). We conclude that this skewed representation in taxonomic abundances reflects taphonomic processes, which should be considered in future DNA-based paleolimnological investigations.

This work aims to determine the profiles of cyanopeptides and anatoxin synthetized by cyanobacteria in the Lithuanian part of the Curonian Lagoon (SE Baltic Sea) and to characterize their spatial and temporal patterns in this ecosystem. Cyanometabolites were analysed by a LC-MS/MS system and were coupled to a hybrid triple quadrupole/linear ion trap mass spectrometer. During the investigation period (2013–2017), 10 microcystins, nodularin, anatoxin-a, 16 anabaenopeptins, including 1 oscillamide, 12 aeruginosins, 1 aeruginosamide, 3 cyanopeptolins and 4 microginins were detected. The most frequently detected metabolites were found at all investigated sites. Demethylated microcystin variants and anabaenopeptins had the strongest relationship with Planktothrix agardhii, while non-demethylated microcystin variants and anatoxin had the strongest relationship with Microcystis spp. Low concentrations of some microcystins: [Asp3]MC-RR, MC-RR, MC-LR, as well as a few other cyanopeptides: AP-A and AEG-A were found during the cold period (December–March). Over the study period, Aphanizomenon, Planktothrix and Microcystis were the main dominant cyanobacteria species, while Planktothrix, Microcystis, and Dolichospermum were potentially producers of cyanopeptides and anatoxin detected in samples from the Curonian Lagoon.

Aphanizomenon sp. ULC602, recently isolated in a Belgian lake, is a filamentous, nitrogen-fixing, freshwater cyanobacterium that is one of the primary producers of cyanotoxins following its bloom formation, causing water contamination. This study aims to evaluate the effects of growing conditions and essential nutrients on the growth of Aphanizomenon sp. ULC602 via its production of chlorophyll-a (Chlo-a). Our results indicated that this bacterium could grow well at temperatures ranging from 18 to 25°C with an optimal pH of 6.0-7.5 under continuous lighting. It grew slowly in the absence of a carbon source or at lower carbon concentrations. The addition of nitrogen from nitrate and urea led to a less than 50% reduction of Chlo-a content compared to the medium lacking nitrogen. The iron bioavailability significantly stimulated the Chlo-a production, but it was saturated by an iron concentration of 0.115 mM. Moreover, a decrease in Chlo-a biomass was observed under sulfur deficiency. The bacterium could not grow well in media containing various phosphorus sources. In conclusion, as the growth and consequent forming bloom of cyanobacteria can be stimulated or inhibited by environmental conditions and eutrophication, our investigation could contribute to further studies to control the blooming of the target bacterium in freshwater., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Pham, Askarzadmohassel and Brandl.)