Sphingobium cyanobacteriorum sp. nov., isolated from fresh water.

A novel Gram-stain-negative, yellow-pigmented, short rod-shaped bacterial strain, HBC34T, was isolated from a freshwater sample collected from Daechung Reservoir, Republic of Korea. The results of 16S rRNA gene sequence analysis indicated that HBC34T was affiliated with the genus Sphingobium and shared the highest sequence similarity to the type strains of Sphingobium vermicomposti (98.01 %), Sphingobium psychrophilum (97.87 %) and Sphingobium rhizovicinum (97.59 %). The average nucleotide identity (ANI) and digital DNA-DNA hybridisation (dDDH) values between HBC34T and species of the genus Sphingobium with validly published names were below 84.01 and 28.1 %, respectively. These values were lower than the accepted species-delineation thresholds, supporting its recognition as representing a novel species of the genus Sphingobium. The major fatty acids (>10 % of the total fatty acids) were identified as summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The main polar lipids were phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, two phospholipids and two unidentified polar lipids. The respiratory quinone was Q-10. The genomic DNA G+C content of HBC34T was 64.04 %. The polyphasic evidence supports the classification of HBC34T as the type strain of a novel species of the genus Sphingobium, for which the name Sphingobium cyanobacteriorum sp. nov is proposed. The type strain is HBC34T (= KCTC 8002T= LMG 33140T).

Beyond the Bloom: Unraveling the Diversity, Overlap, and Stability of Free-Living and Particle-Attached Bacterial Communities in a Cyanobacteria-Dominated Hypereutrophic Lake.

In aquatic ecosystems with low nutrient levels, organic aggregates (OAs) act as nutrient hotspots, hosting a diverse range of microbial species compared to those in the water column. Lake eutrophication, marked by intensified and prolonged cyanobacterial blooms, significantly impacts material and energy cycling processes, potentially altering the ecological traits of both free-living (FL) and particle-attached (PA) bacteria. However, the extent to which observed patterns of FL and PA bacterial diversity, community assembly, and stability extend to hypereutrophic lakes remains understudied. To address this gap, we investigated bacterial diversity, composition, assembly processes, and stability within hypereutrophic Lake Xingyun. Our results revealed that FL bacterial communities exhibited higher α-diversity than PA counterparts, coupled with discernible taxonomic compositions. Both bacterial communities showed distinct seasonality, influenced by cyanobacterial bloom intensity. Environmental factors accounted for 71.1% and 54.2% of the variation among FL and PA bacteria, respectively. The assembly of the PA bacterial community was predominantly stochastic, while FL assembly was more deterministic. The FL network demonstrated greater stability, complexity, and negative interactions, indicative of competitive relationships, while the PA network showed a prevalence of positive correlations, suggesting mutualistic interactions. Importantly, these findings differ from observations in oligotrophic, mesotrophic, and eutrophic lakes. Overall, this research provides valuable insights into the interplay among bacterial fractions, enhancing our understanding of nutrient status and cyanobacterial blooms in shaping bacterial communities.

Satellite Tracking Reveals the Speed Up of the Lacustrine Algal Bloom Drift in Response to Climate Change.

Satellite evidence indicates a global increase in lacustrine algal blooms. These blooms can drift with winds, resulting in significant changes of the algal biomass spatial distribution, which is crucial in bloom formation. However, the lack of long-term, large-scale observational data has limited our understanding of bloom drift. Here, we have developed a novel method to track the drift using multi-source remote sensing satellites and presented a comprehensive bloom drift data set for four typical lakes: Lake Taihu (China, 2011-2021), Lake Chaohu (China, 2011-2020), Lake Dianchi (China, 2003-2021), and Lake Erie (North America, 2003-2021). We found that blooms closer to the water surface tend to drift faster. Higher temperatures and lower wind speeds bring blooms closer to the water surface, therefore accelerating drift and increasing biomass transportation. Under ongoing climate change, algal blooms are increasingly likely to spread over larger areas and accumulate in downwind waters, thereby posing a heightened risk to water resources. Our research greatly improves the understanding of algal bloom dynamics and provides new insights into the driving factors behind the global expansion of algal blooms. Our bloom-drift-tracking methodology also paves the way for the development of high-precision algal bloom prediction models.

Biotechnological approaches for suppressing Microcystis blooms: insights and challenges.

Cyanobacterial harmful algal blooms, particularly those dominated by Microcystis, pose significant ecological and health risks worldwide. This review provides an overview of the latest advances in biotechnological approaches for mitigating Microcystis blooms, focusing on cyanobactericidal bacteria, fungi, eukaryotic microalgae, zooplankton, aquatic plants, and cyanophages. Recently, promising results have been obtained using cyanobactericidal bacteria: not through the inoculation of cultured bacteria, but rather by nurturing those already present in the periphyton or biofilms of aquatic plants. Fungi and eukaryotic microalgae also exhibit algicidal properties; however, their practical applications still face challenges. Zooplankton grazing on Microcystis can improve water quality, but hurdles exist because of the colonial form and toxin production of Microcystis. Aquatic plants control blooms through allelopathy and nutrient absorption. Although cyanophages hold promise for Microcystis control, their strain-specificity hinders widespread use. Despite successful laboratory validation, field applications of biological methods are limited. Future research should leverage advanced molecular and bioinformatic techniques to understand microbial interactions during blooms and offer insights into innovative control strategies. Despite progress, the efficacy of biological methods under field conditions requires further verification, emphasizing the importance of integrating advanced multi-meta-omics techniques with practical applications to address the challenges posed by Microcystis blooms. KEY POINTS: • A diverse range of biotechnological methods is presented for suppressing Microcystis blooms. • Efficacy in laboratory experiments needs to be proved further in field applications. • Multi-meta-omics techniques offer novel insights into Microcystis dynamics and interactions.

Undibacterium cyanobacteriorum sp. nov., an auxin-producing bacterium isolated from fresh water during cyanobacterial bloom period.

A novel Gram-negative, white-pigmented, and auxin-producing strain, 20NA77.5T, was isolated from fresh water during cyanobacterial bloom period. Pairwise comparison of the 16S rRNA gene sequences showed that strain 20NA77.5T belonged to the genus Undibacterium and exhibited the highest sequence similarity to the type strains of Undibacterium danionis (98.00%), Undibacterium baiyunense (97.93%), Undibacterium macrobrachii (97.92%), and Undibacterium fentianense (97.71%). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain 20NA77.5T and its related type strains were below 79.93 and 23.80%, respectively. The predominant fatty acids (> 10% of the total fatty acids) were C16:0 and summed feature 3 (C16:1ω7c and/or C16:1ω6c). The genomic DNA G + C content of strain 20NA77.5T was found to be 48.61%. Based on the phylogenetic distinctness, chemotaxonomic features, and phenotypic features, strain 20NA77.5T is considered to represent a novel species of the genus Undibacterium, for which the name Undibacterium cyanobacteriorum sp. nov is proposed. The type strain is 20NA77.5T (= KCTC 8005T = LMG 33136T).

Sustainable control of Microcystis aeruginosa, a harmful cyanobacterium, using Selaginella tamariscina extracts.

Eco-friendly reagents derived from plants represent a promising strategy to mitigate the occurrence of toxic cyanobacterial blooms. The use of an amentoflavone-containing Selaginella tamariscina extract (STE) markedly decreased the number of Microcystis aeruginosa cells, thus demonstrating significant anti-cyanobacterial activity. In particular, the Microcystis-killing fraction obtained from pulverized S. tamariscina using hot-water-based extraction at temperatures of 40 °C induced cell disruption in both axenic and xenic M. aeruginosa. Liquid chromatographic analysis was also conducted to measure the concentration of amentoflavone in the STE, thus supporting the potential M. aeruginosa-specific killing effects of STE. Bacterial community analysis revealed that STE treatment led to a reduction in the relative abundance of Microcystis species while also increasing the 16S rRNA gene copy number in both xenic M. aeruginosa NIBR18 and cyanobacterial bloom samples isolated from a freshwater environment. Subsequent testing on bacteria, cyanobacteria, and algae isolated from freshwater revealed that STE was not toxic for other taxa. Furthermore, ecotoxicology assessment involving Aliivibrio fischeri, Daphnia magna, and Danio rerio found that high STE doses immobilized D. magna but did not impact the other organisms, while there was no change in the water quality. Overall, due to its effective Microcystis-killing capability and low ecotoxicity, aqueous STE represents a promising practical alternative for the management of Microcystis blooms.

Ecological Dynamics of Broad- and Narrow-Host-Range Viruses Infecting the Bloom-Forming Toxic Cyanobacterium Microcystis aeruginosa.

Microcystis aeruginosa is predicted to interact and coexist with diverse broad- and narrow-host-range viruses within a bloom; however, little is known about their affects on Microcystis population dynamics. Here, we developed a real-time PCR assay for the quantification of these viruses that have different host ranges. During the sampling period, total Microcystis abundance showed two peaks in May and August with a temporary decrease in June. The Microcystis population is largely divided into three phylotypes based on internal transcribed sequences (ITS; ITS types I to III). ITS I was the dominant phylotype (66% to 88%) except in June. Although the ITS II and III phylotypes were mostly less abundant, these phylotypes temporarily increased to approximately equivalent abundances of the ITS I population in June. During the same sampling period, the abundances of the broad-host-range virus MVGF_NODE331 increased from April to May and from July to October with a temporary decrease in June, in which its dynamics were in proportion to the increase of total Microcystis abundances regardless of changes in host ITS population composition. In contrast, the narrow-host-range viruses MVG_NODE620 and Ma-LMM01 were considerably less abundant than the broad-host-range virus and generally did not fluctuate in the environment. Considering that M. aeruginosa could increase the abundance and sustain the bloom under the prevalence of the broad-host-range virus, host abundant and diverse antiviral mechanisms might contribute to coexistence with its viruses. IMPORTANCE The bloom-forming toxic cyanobacterium Microcystis aeruginosa interacts with diverse broad- and narrow-host-range viruses. However, the dynamics of the Microcystis population (at the intraspecies level) and viruses with different host ranges remain unknown. Our real-time PCR assays unveiled that the broad-host-range virus gradually increased in abundance over the sampling period, in proportion to the increase in total Microcystis abundance regardless of changes in genotypic composition. The narrow-host-range viruses were considerably less abundant than the broad-host-range virus and did not generally fluctuate in the environment. The expansion and maintenance of the Microcystis bloom even under the increased infection by the broad-host-range virus suggested that highly abundant and diverse antiviral mechanisms allowed them to coexist with viruses under selective pressure. This paper expands our knowledge about the ecological dynamics of Microcystis viruses and provides potential insights into their coexistence with their host.

Vibrio floridensis sp. nov., a novel species closely related to the human pathogen Vibrio vulnificus isolated from a cyanobacterial bloom.

A Gram-stain-negative, rod-shaped bacterial strain, designated Vibrio floridensis IRLE0018 (=NRRL B-65642=NCTC 14661), was isolated from a cyanobacterial bloom along the Indian River Lagoon (IRL), a large and highly biodiverse estuary in eastern Florida (USA). The results of phylogenetic, biochemical, and phenotypic analyses indicate that this isolate is distinct from species of the genus Vibrio with validly published names and is the closest relative to the emergent human pathogen, Vibrio vulnificus. Here, we present the complete genome sequence of V. floridensis strain IRLE0018 (4 535 135 bp). On the basis of the established average nucleotide identity (ANI) values for the determination of different species (ANI <95 %), strain IRLE0018, with an ANI of approximately 92 % compared with its closest relative, V. vulnificus, represents a novel species within the genus Vibrio. To our knowledge, this represents the first time this species has been described. The results of genomic analyses of V. floridensis IRLE0018 indicate the presence of antibiotic resistance genes and several known virulence factors, however, its pathogenicity profile (e.g. survival in serum, phagocytosis avoidance) reveals limited virulence potential of this species in contrast to V. vulnificus.

Cyanosphere Dynamic During Dolichospermum Bloom: Potential Roles in Cyanobacterial Proliferation.

Under the effect of global change, management of cyanobacterial proliferation becomes increasingly pressing. Given the importance of interactions within microbial communities in aquatic ecosystems, a handful of studies explored the potential relations between cyanobacteria and their associated bacterial community (i.e., cyanosphere). Yet, most of them specifically focused on the ubiquitous cyanobacteria Microcystis, overlooking other genera. Here, based on 16s rDNA metabarcoding analysis, we confirmed the presence of cyanosphere representing up to 30% of the total bacterial community diversity, during bloom episode of another preponderant cyanobacterial genus, Dolichospermum. Moreover, we highlighted a temporal dynamic of this cyanosphere. A sPLS-DA model permits to discriminate three important dates and 220 OTUs. With their affiliations, we were able to show how these variations potentially imply a turnover in ecological functions depending on bloom phases. Although more studies are necessary to quantify the impacts of these variations, we argue that cyanosphere can have an important, yet underestimated, role in the modulation of cyanobacterial blooms.

From natural to artificial cyanophages: Current progress and application prospects.

The over proliferation of harmful cyanobacteria and their cyanotoxins resulted in damaged aquatic ecosystem, polluted drinking water and threatened human health. Cyanophages are a kind of viruses that exclusively infect cyanobacteria, which is considered as a potential strategy to deal with cyanobacterial blooms. Nevertheless, the infecting host range and/or lysis efficiency of natural cyanophages is limited, rising the necessity of constructing non-natural cyanophages via artificial modification, design and synthesis to expand their host range and/or efficiency. The paper firstly reviewed representative cyanophages such as P60 with a short latent period of 1.5 h and S-CBS1 having a burst size up to 200 PFU/cell. To explore the in-silico design principles, we critically summarized the interactions between cyanophages and the hosts, indicating modifying the recognized receptors, enhancing the adsorption ability, changing the lysogeny and excluding the defense of hosts are important for artificial cyanophages. The research progress of synthesizing artificial cyanophages were summarized subsequently, raising the importance of developing genetic manipulation technologies and their rescue strategies in the future. Meanwhile, Large-scale preparation of cyanophages for bloom control is a big challenge. The application prospects of artificial cyanophages besides cyanobacteria bloom control like adaptive evolution and phage therapy were discussed at last. The review will promote the design, synthesis and application of cyanophages for cyanobacteria blooms, which may provide new insights for the related water pollution control and ensuring hydrosphere security.

Patterns of free-living and particle-attached bacteria along environmental gradients in Lake Taihu.

To elucidate the effects of environmental heterogeneity on diversity, composition, and degree of overlap between free-living (FL) and particle-attached (PA) bacteria, we sampled large, shallow, eutrophic Lake Taihu, China across gradients spanning riverine inflow, cyanobacterial blooms, and the open limnetic area. Using high-throughput sequencing of the 16S rRNA gene, we show that (i) bacterial communities near riverine inflow had high α-diversity and a high degree of overlap between FL and PA lifestyles, (ii) communities in cyanobacterial blooms have reduced α-diversity within the PA lifestyle, and (iii) communities from the limnetic area had the lowest bacterial α-diversity within the FL lifestyle and a medium degree of overlap between the FL and PA lifestyles. Redundancy analysis showed that the variation of the FL bacterial community was shaped by suspended solids and total phosphorous, while the variation of the PA bacterial community was shaped by suspended solids, dissolved oxygen, and the percentage of organic matter in suspended solids. This study highlights the importance of environmental heterogeneity, riverine input, cyanobacterial blooms, and nutrient status on the spatial distribution patterns of FL and PA bacterial communities in freshwater lakes.

Damage mechanism of calcium peroxide on Microcystis aeruginosa PCC7806 and its potential application.

Calcium peroxide (CP) is an oxidizing agent that can gradually release hydrogen peroxide (HP) to achieve selective killing of cyanobacteria in water blooms, and reduce the phosphorus content in the water column. Despite the potential of CP for use in cyanobacterial water bloom disposal, there is a lack of research on the mechanism of oxidative damage on cyanobacterial cells by calcium peroxide. Further studies are required to comprehend the underlying scientific principles and potential risks and benefits of applying this approach to cyanobacteria disposal. In this investigation, we employed varying doses of CP for the treatment of Microcystis aeruginosa (M. aeruginosa), which resulted in the following findings: (1) the HP released from CP can damage the photosystem II of M. aeruginosa, reduce cell photosynthetic pigment content, intensify the degree of membrane lipid peroxidation, and increase the extracellular protein content; (2) CP significantly increased the soluble extracellular polysaccharide (sEPS) and bound extracellular polysaccharide (bEPS) content of cells (p < 0.05), causing the cells to exist as agglomerates and effectively allowing them to flocculate and precipitate, reducing the turbidity of the water body; (3) The increased dose elevated the pH and calcium ions significantly decreased the orthophosphate content, resulting in an increase in extracellular alkaline phosphatase activity, but possibly increasing the total extracellular nitrogen content. These results suggested that CP is an effective chemical algaecide for cyanobacteria, and has the potential to be applied to dispose of cyanobacterial blooms while reducing the phosphorus content of the water column and further inhibiting the growth and proliferation of cells.

Hymenobacter cyanobacteriorum sp. nov., isolated from a freshwater reservoir during the cyanobacterial bloom period.

A Gram-negative, red-colored, and rod-shaped bacterial strain, DH14T, was isolated from a eutrophic reservoir. The 16S rRNA gene sequence analysis showed that strain DH14T was most closely related to Hymenobacter terrigena (98.3% similarity) and Hymenobacter terrae (98.1%). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain DH14T and its related type strains were below 82.9% and 27.2%, respectively. Strain DH14T contained iso-C15:0 (32.6%), anteiso-C15:0 (14.0%), and summed feature 3 (C16:1 ω6c and/or C16:1 ω7c) (25.8%) as major cellular fatty acids. The main polar lipids were phosphatidylethanolamine, two unidentified aminophospholipids, and one unidentified lipid. The respiratory quinone was menaquinone 7 (MK-7). The genomic DNA G + C content was 62.1%. These evidences support the classification of strain DH14T as a novel species in the genus Hymenobacter, for which the name Hymenobacter cyanobacteriorum sp. nov. is proposed. The type strain is DH14T (= KCTC 92040T = LMG 32425T).

Black blooms-induced adaptive responses of sulfate reduction bacteria in a shallow freshwater lake.

Decomposing cyanobacterial bloom-induced black blooms been seen as an issue in the management of freshwater ecosystems, but its effect on sulfate-reducing bacteria (SRB) in shallow freshwater lakes is not clear. The objective of this study is to present an in-depth investigation of black bloom effects on the activities and composition of SRB, as well as the interactions between SRB and other bacteria. Water and surface sediments samples were collected from a shallow freshwater lake during black and non-black blooms. Sulfate reduction rates (SRRs) in the water column were determined from the linear regression of sulfate depletion with time. Quantitative real-time polymerase chain reactions (qPCRs), targeting the dsrA gene and Illumina sequencing of 16S rDNA, were used to estimate the SRB population and SRB community structures, respectively. Our data indicate that although a higher abundance of SRB was responsible for the higher SRR in the bottom water (34.09 ±â€¯2.37 nmol mL-1 day-1) than in the surface water (14.57 ±â€¯2.91 nmol mL-1 day-1) during black blooms, cell-specific sulfate reduction rates (csSRRs) in the distinct water layers were not significantly different (P = 0.95), with the value of approximately 0.017 fmol cell-1 day-1. Additionally, Desulfomicrobium and Desulfovibrio were the two main genera of SRB in the water column during black bloom season, while Desulfobulbus, Desulfobacca and Desulfatiglans genera were identified in the sediments of both the black and non-black blooms in genera pools. Each SRB genus preferentially associated with bacteria for specific functions in the bacterial co-occurrence network, regardless of whether black booms occurred or not. These results extend our knowledge on the importance of SRB during black blooms and the adaptation of SRB to environmental changes in freshwater lakes.

Community succession during the preventive control of cyanobacterial bloom by hydrogen peroxide in an aquatic microcosm.

Hydrogen peroxide (H2O2) is an environmentally friendly algaecide with good prospects for cyanobacterial bloom control. In this study, 0.2-1.5 mg L-1 of H2O2 was applied to an aquatic microcosm containing cyanobacteria, bacteria, and eukaryotic phytoplankton at the early cyanobacterial growth stage·H2O2 generated hormesis in cyanobacteria at 0.2 mg L-1; significantly (p < 0.05) inhibited cyanobacterial growth, cyanobacterial photosynthesis, and microcystin production at 0.5-1.5 mg L-1; and effectively prevented the formation of cyanobacterial bloom without generating adverse effects on eukaryotic phytoplankton at 1.0 and 1.5 mg L-1. Application of 0.5-1.5 mg L-1 H2O2 directly inhibited the abundance of five typical bloom-forming cyanobacterial genera (Microcystis, Anabeana, Synechococcus, Nostoc, and Oscillatoria), which were negatively correlated with four bacterial genera (Actinotalea, Flavobacterium, Fluviicola, and Exiguobacterium) and five eukaryotic phytoplankton genera (Cyclotella, Desmodesmus, Dinobryon, Fragilaria, and Mychonastes) and positively correlated with six proteobacterial genera (Brevundimonas, Devosia, Limnohabitans, Porphyrobacter, Pseudomonas, and Rhodobacter). After application of 1.0 and 1.5 mg L-1 H2O2 for 15 days, H2O2-treated groups showed significantly (p < 0.05) different prokaryotic community structures from that of the control group at the bloom stage (15th day), while eukaryotic community structures in H2O2-treated groups remained stable and showed high similarity with that of the control group at a non-bloom stage (5th day). Application of low-dose H2O2 during the early cyanobacterial growth stage could effectively prevent the formation of cyanobacterial blooms without disrupting non-target organisms.

Utilization of GOCI data to evaluate the diurnal vertical migration of Microcystis aeruginosa and the underlying driving factors.

Cyanobacterial blooms are one of the most severe ecological problems affecting lakes. The vertical migration of cyanobacteria in the water column increases the uncertainty in the formation and disappearance of blooms, which may be closely associated with light, temperature, and wind speed. However, it is difficult to quantitatively evaluate the influencing factors of cyanobacteria vertical movement in natural environment compared to the laboratory experimental environment. Besides, both field survey and laboratory experiment method have the difficulties in determining the diurnal vertical migration of cyanobacteria at the synoptic lake scale. In this study, based on the diurnal dynamics of cyanobacterial bloom intensity (CBI) observed by the Geostationary Ocean Color Imager (GOCI) from 2011 to 2019, the daily variations, floating rate, and sinking rate of Microcystis aeruginosa were calculated in the natural environment. Then, the effects of light, temperature, and wind speed on the vertical migration of M. aeruginosa were analysed from the perspectives of day, night, and season. The results are as follows: the records of three typical patterns of diurnal CBI exhibited strong seasonal variability from the 9-year statistics; at night, the buoyancy recovery rate of cyanobacterial colonies increased with temperature, so that at temperature >15 °C and wind speed <3 m s-1, CBI reached the maximum of the whole day at 08:16; the sinking rate of M. aeruginosa was positively correlated with the cumulated light energy at both synoptic and pixel scale; the upward migration speed of M. aeruginosa was positively correlated with the maximum wind speed of the day before cyanobacterial bloom. Therefore, the severer cyanobacterial blooms were often observed by satellite images after strong winds. The analysis of diurnal variation, floating rate, and sinking rate of M. aeruginosa will expand our knowledge for further understanding the formation mechanism of cyanobacterial blooms and for improving the accuracy of model simulation to predict the hourly changes in cyanobacterial blooms in Lake Taihu.

Niveibacterium microcysteis sp. nov., isolated from a cyanobacterial bloom sample.

A novel bacterial strain, named HC41T, was isolated from a cyanobacterial bloom sample and was characterized as Gram-stain-negative, rod-shaped and non-motile. According to 16S rRNA phylogenetic analyses, this strain HC41T belongs to the family Rhodocyclaceae and is most closely related to Niveibacterium umoris KACC 17062T (=MIC 2059T; 98.63 %) and Uliginosibacterium gangwonense 5YN10-9 T (=KACC 11603T; 93.64 %). The genome size and DNA G+C content of strain HC41T were 4.8 Mbp and 64.17 mol%, respectively. Moreover, the average nucleotide identity, digital DNA-DNA hybridization and amino acid identity values between strain HC41T and N. umoris KACC 17062T were 81.8, 43.1 and 90.89 %, respectively. Additionally, strain HC41T exhibited weak catalase and oxidase activities and had no motility (swimming and swarming motilities). The cells grew at 11-40 °C (optimum, 30 °C), pH 5.5-8.0 (optimum, pH 7) and with 0-1.0 % (w/v) NaCl (optimum, 0 % NaCl) in Reasoner's 2A medium. Its major respiratory quinone was ubiquinone-8 and its major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. Furthermore, C16 : 0 and summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c; C16 : 1 ω6c and/or C16 : 1 ω7c) were the predominant cellular fatty acids in strain HC41T according to fatty acid methyl ester analysis. Based on its genotypic and phenotypic characteristics, strain HC41T was identified as representing a novel Niveibacterium species, for which the name Niveibacterium microcysteis sp. nov. is proposed (=KACC 22091T=DSM 111425T).

Dynamics of the prokaryotic and eukaryotic microbial community during a cyanobacterial bloom.

Toxic cyanobacterial blooms frequently develop in eutrophic freshwater bodies worldwide. Microcystis species produce microcystins (MCs) as a cyanotoxin. Certain bacteria that harbor the mlr gene cluster, especially mlrA, are capable of degrading MCs. However, MC-degrading bacteria may possess or lack mlr genes (mlr+ and mlr- genotypes, respectively). In this study, we investigated the genotype that predominantly contributes to biodegradation and cyanobacterial predator community structure with change in total MC concentration in an aquatic environment. The 2 genotypes coexisted but mlr+ predominated, as indicated by the negative correlation between mlrA gene copy abundance and total MC concentration. At the highest MC concentrations, predation pressure by Phyllopoda, Copepoda, and Monogononta (rotifers) was reduced; thus, MCs may be toxic to cyanobacterial predators. The results suggest that cooperation between MC-degrading bacteria and predators may reduce Microcystis abundance and MC concentration.

DNA damage induced by cylindrospermopsin on different tissues of the biomonitor fish Poecilia reticulata.

The cyanotoxin cylindrospermopsin (CYN) is the second biggest cause of poisoning worldwide, both in humans and animals. Although CYN primarily affects the aquatic environments and can be absorbed in fishes by multiple routes, data reporting its toxicity and mechanism of action are still scarce in this group. Using P. reticulata as model species, it was evaluated whether CYN promotes mutagenic and genotoxic effects in different fish target tissues. Adult females were exposed in a static way to 0 (control), 0.5, 1.0, and 1.5 µg L-1 of pure CYN for 24 and 96 hours. For the first time, DNA damage was detected in fish brain after CYN exposition. In brain cells, a concentration-response DNA damage was observed for both exposure times, suggesting a direct or indirect action of CYN in neurotoxicity. For the liver cells, 96 hours caused an increase in DNA damage, as well the highest percentage of DNA in the tail was reached when used 1.5 µg L-1 of CYN. In peripheral blood cells, an increase in DNA damage was observed for all tested concentrations after 96 hours. In erythrocytes, micronuclei frequency was higher at 1.5 µg L-1 treatment while the erythrocyte nuclear abnormalities (ENA) frequency was significantly higher even at the lowest CYN concentration. Such data demonstrated that acute exposition to CYN promotes genotoxicity in the brain, liver, and blood cells of P. reticulata, as well mutagenicity in erythrocytes. It rises an alert regarding to the toxic effects of CYN for aquatic organisms as well as for human health.

Predicting Cyanobacterial Blooms Using Hyperspectral Images in a Regulated River.

Process-based modeling for predicting harmful cyanobacteria is affected by a variety of factors, including the initial conditions, boundary conditions (tributary inflows and atmosphere), and mechanisms related to cyanobacteria growth and death. While the initial conditions do not significantly affect long-term predictions, the initial cyanobacterial distribution in water is particularly important for short-term predictions. Point-based observation data have typically been used for cyanobacteria prediction of initial conditions. These initial conditions are determined through the linear interpolation of point-based observation data and may differ from the actual cyanobacteria distribution. This study presents an optimal method of applying hyperspectral images to establish the Environmental Fluid Dynamics Code-National Institute of Environment Research (EFDC-NIER) model initial conditions. Utilizing hyperspectral images to determine the EFDC-NIER model initial conditions involves four steps that are performed sequentially and automated in MATLAB. The EFDC-NIER model is established using three grid resolution cases for the Changnyeong-Haman weir section of the Nakdong River Basin, where Microcystis dominates during the summer (July to September). The effects of grid resolution on (1) water quality modeling and (2) initial conditions determined using cumulative distribution functions are evaluated. Additionally, the differences in Microcystis values are compared when applying initial conditions using hyperspectral images and point-based evaluation data. Hyperspectral images allow detailed initial conditions to be applied in the EFDC-NIER model based on the plane-unit cyanobacterial information observed in grids, which can reduce uncertainties in water quality (cyanobacteria) modeling.