The population genetic structure and phylogeographic dispersal of Nodularia breviconcha in the Korean Peninsula based on COI and 16S rRNA genes.

A freshwater mussel, Nodularia breviconcha (Mollusca: Bivalvia: Unionida) is endemic to Korean Peninsula. It has recently been taxonomically reexamined and elevated from a subspecies of N. douglasiae to an independent species. But population genetic studies for the species have rarely been conducted. To explore the population genetic structure of N. breviconcha, the nucleotide sequences of cytochrome oxidase subunit I(COI) and 16S rRNA genes from 135 N. breviconcha individuals, including 52 from this study and 83 from Choi et al. (2020). We found 23 COI and 11 16S rRNA genes haplotypes. Phylogeny, TCS network, Principal coordinates analysis, and spatial analysis of molecular variance performed with COI gene indicated that there are exist three different genetic lineages in the N. breviconcha populations: West lineage, Southwest lineage, and Southeast lineage. According to the time calibrated phylogeny, they are likely to be diverged during the late Miocene (8-6 Ma). Geographical distribution patterns of the three genetic lineages may be related to the formation of Taebaek and Sobaek-Noryeong mountain ranges in the Korean Peninsula occurred during the Miocene (30-10 Ma). The present results of this study will be helpful not only for the conservation, but also for the exploration of the population genetic structure of endemic freshwater mussels in the Korean Peninsula.

Detection and Characterization of Nodularin by Using Label-Free Surface-Enhanced Spectroscopic Techniques.

Nodularin (NOD) is a potent toxin produced by Nodularia spumigena cyanobacteria. Usually, NOD co-exists with other microcystins in environmental waters, a class of cyanotoxins secreted by certain cyanobacteria species, which makes identification difficult in the case of mixed toxins. Herein we report a complete theoretical DFT-vibrational Raman characterization of NOD along with the experimental drop-coating deposition Raman (DCDR) technique. In addition, we used the vibrational characterization to probe SERS analysis of NOD using colloidal silver nanoparticles (AgNPs), commercial nanopatterned substrates with periodic inverted pyramids (KlariteTM substrate), hydrophobic Tienta® SpecTrimTM slides, and in-house fabricated periodic nanotrenches by nanoimprint lithography (NIL). The 532 nm excitation source provided more well-defined bands even at LOD levels, as well as the best performance in terms of SERS intensity. This was reflected by the results obtained with the KlariteTM substrate and the silver-based colloidal system, which were the most promising detection approaches, providing the lowest limits of detection. A detection limit of 8.4 × 10-8 M was achieved for NOD in solution by using AgNPs. Theoretical computation of the complex vibrational modes of NOD was used for the first time to unambiguously assign all the specific vibrational Raman bands.

Interspecific Interactions Drive Nonribosomal Peptide Production in Nodularia spumigena.

Nodularia spumigena is a bloom-forming cyanobacterium that produces several classes of nonribosomal peptides (NRPs) that are biologically active; however, the ecological roles of specific NRPs remain largely unknown. Here, we explored the involvement of NRPs produced by N. spumigena in interspecific interactions by coculturing the cyanobacterium and its algal competitors, the diatom Phaeodactylum tricornutum and the cryptomonad Rhodomonas salina, and measuring NRP levels and growth responses in all three species. Contrary to the expected growth suppression in the algae, it was N. spumigena that was adversely affected by the diatom, while the cryptomonad had no effect. Reciprocal effects of N. spumigena on the algae were manifested as the prolonged lag phase in R. salina and growth stimulation in P. tricornutum; however, these responses were largely attributed to elevated pH and not to specific NRPs. Nevertheless, the NRP levels in the cocultures were significantly higher than in the monocultures, with an up to 5-fold upregulation of cell-bound nodularins and exudation of nodularin and anabaenopeptin. Thus, chemically mediated interspecific interactions can promote NRP production and release by cyanobacteria, resulting in increased input of these compounds into the water. IMPORTANCE NRPs were involved in growth responses of both cyanobacteria and algae; however, the primary driver of the growth trajectories was high pH induced by N. spumigena. Thus, the pH-mediated inhibition of eukaryotic phytoplankton may be involved in the bloom formation of N. spumigena. We also report, for the first time, the reciprocal growth inhibition of N. spumigena by diatoms resistant to alkaline conditions. As all species in this study can co-occur in the Baltic Sea during summer, these findings are highly relevant for understanding ecological interactions in planktonic communities in this and other systems experiencing regular cyanobacteria blooms.

Potent Inhibitor of Human Trypsins from the Aeruginosin Family of Natural Products.

Serine proteases regulate many physiological processes and play a key role in a variety of cancers. Aeruginosins are a family of natural products produced by cyanobacteria that exhibit pronounced structural diversity and potent serine protease inhibition. Here, we sequenced the complete genome of Nodularia sphaerocarpa UHCC 0038 and identified the 43.7 kb suomilide biosynthetic gene cluster. Bioinformatic analysis demonstrated that suomilide belongs to the aeruginosin family of natural products. We identified 103 complete aeruginosin biosynthetic gene clusters from 12 cyanobacterial genera and showed that they encode an unexpected chemical diversity. Surprisingly, purified suomilide inhibited human trypsin-2 and -3, with IC50 values of 4.7 and 11.5 nM, respectively, while trypsin-1 was inhibited with an IC50 of 104 nM. Molecular dynamics simulations suggested that suomilide has a long residence time when bound to trypsins. This was confirmed experimentally for trypsin-1 and -3 (residence times of 1.5 and 57 min, respectively). Suomilide also inhibited the invasion of aggressive and metastatic PC-3M prostate cancer cells without affecting cell proliferation. The potent inhibition of trypsin-3, together with a long residence time and the ability to inhibit prostate cancer cell invasion, makes suomilide an attractive drug lead for targeting cancers that overexpress trypsin-3. These results substantially broaden the genetic and chemical diversity of the aeruginosin family and suggest that aeruginosins may be a source of selective inhibitors of human serine proteases.

Changes in Growth, Photosynthesis Performance, Pigments, and Toxin Contents of Bloom-Forming Cyanobacteria after Exposure to Macroalgal Allelochemicals.

Macroalgae can directly restrict the growth of various phytoplankton species by releasing allelopathic compounds; therefore, considerable attention should be paid to the allelopathic potential of these organisms against harmful and bloom-forming cyanobacteria. The main aim of this study was to demonstrate for the first time the allelopathic activity of Ulva intestinalis on the growth, the fluorescence parameters: the maximum PSII quantum efficiency (Fv/Fm) and the effective quantum yield of PSII photochemistry (ΦPSII), the chlorophyll a (Chl a) and carotenoid (Car) content, and the microcystin-LR (MC-LR) and phenol content of three bloom-forming cyanobacteria, Aphanizomenon sp., Nodularia spumigena, and Nostoc sp. We found both negative and positive allelopathic effects of U. intestinalis on tested cyanobacteria. The study clearly showed that the addition of the filtrate of U. intestinalis significantly inhibited growth, decreased pigment content and Fv/Fm and ΦPSII values of N. spumigena and Nostoc sp., and stimulated Aphanizomenon sp. The addition of different concentrations of aqueous extract also stimulated the cyanobacterial growth. It was also shown that the addition of extract obtained from U. intestinalis caused a significant decrease in the MC-LR content in Nostoc sp. cells. Moreover, it the phenol content in N. spumigena cells was increased. On the other hand, the cell-specific phenol content for Aphanizomenon sp. decreased due to the addition of the filtrate. In this work, we demonstrated that the allelopathic effect of U. intestinalis depends on the target species' identity as well as the type of allelopathic method used. The study of the allelopathic Baltic macroalgae may help to identify their possible role as a significant biological factor influencing harmful cyanobacterial blooms in brackish ecosystems.

Competitive interactions as a mechanism for chemical diversity maintenance in Nodularia spumigena.

Nodularia spumigena is a bloom-forming diazotrophic cyanobacterium inhabiting brackish waters worldwide. This species produces non-ribosomal peptides (NRPs), including the hepatotoxin nodularin, often referred to as cyanotoxin. Several known classes of NRPs have various biological activities, although their modes of action are poorly understood. In the Baltic N. spumigena, there is a high NRP chemodiversity among strains, allowing their grouping in specific chemotypes and subgroups. Therefore, it is relevant to ask whether the NRP production is affected by intraspecific interactions between the co-existing strains. Using a novel approach that combines culture technique and liquid chromatography-tandem mass spectrometry for the NRP analysis, we examined N. spumigena strains under mono- and co-culture conditions. The test strains were selected to represent N. spumigena belonging to the same or different chemotype subgroups. In this setup, we observed physiological and metabolic responses in the test strains grown without cell contact. The changes in NRP levels to co-culture conditions were conserved within a chemotype subgroup but different between the subgroups. Our results suggest that intraspecific interactions may promote a chemical diversity in N. spumigena population, with higher NRP production compared to a single-strain population. Studying allelochemical signalling in this cyanobacterium is crucial for understanding toxicity mechanisms and plankton community interactions in the Baltic Sea and other aquatic systems experiencing regular blooms.

Harmful algal blooms and their effects in coastal seas of Northern Europe.

Harmful algal blooms (HAB) are recurrent phenomena in northern Europe along the coasts of the Baltic Sea, Kattegat-Skagerrak, eastern North Sea, Norwegian Sea and the Barents Sea. These HABs have caused occasional massive losses for the aquaculture industry and have chronically affected socioeconomic interests in several ways. This status review gives an overview of historical HAB events and summarises reports to the Harmful Algae Event Database from 1986 to the end of year 2019 and observations made in long term monitoring programmes of potentially harmful phytoplankton and of phycotoxins in bivalve shellfish. Major HAB taxa causing fish mortalities in the region include blooms of the prymnesiophyte Chrysochromulina leadbeateri in northern Norway in 1991 and 2019, resulting in huge economic losses for fish farmers. A bloom of the prymesiophyte Prymnesium polylepis (syn. Chrysochromulina polylepis) in the Kattegat-Skagerrak in 1988 was ecosystem disruptive. Blooms of the prymnesiophyte Phaeocystis spp. have caused accumulations of foam on beaches in the southwestern North Sea and Wadden Sea coasts and shellfish mortality has been linked to their occurrence. Mortality of shellfish linked to HAB events has been observed in estuarine waters associated with influx of water from the southern North Sea. The first bloom of the dictyochophyte genus Pseudochattonella was observed in 1998, and since then such blooms have been observed in high cell densities in spring causing fish mortalities some years. Dinoflagellates, primarily Dinophysis spp., intermittently yield concentrations of Diarrhetic Shellfish Toxins (DST) in blue mussels, Mytilus edulis, above regulatory limits along the coasts of Norway, Denmark and the Swedish west coast. On average, DST levels in shellfish have decreased along the Swedish and Norwegian Skagerrak coasts since approximately 2006, coinciding with a decrease in the cell abundance of D. acuta. Among dinoflagellates, Alexandrium species are the major source of Paralytic Shellfish Toxins (PST) in the region. PST concentrations above regulatory levels were rare in the Skagerrak-Kattegat during the three decadal review period, but frequent and often abundant findings of Alexandrium resting cysts in surface sediments indicate a high potential risk for blooms. PST levels often above regulatory limits along the west coast of Norway are associated with A. catenella (ribotype Group 1) as the main toxin producer. Other Alexandrium species, such as A. ostenfeldii and A. minutum, are capable of producing PST among some populations but are usually not associated with PSP events in the region. The cell abundance of A. pseudogonyaulax, a producer of the ichthyotoxin goniodomin (GD), has increased in the Skagerrak-Kattegat since 2010, and may constitute an emerging threat. The dinoflagellate Azadinium spp. have been unequivocally linked to the presence of azaspiracid toxins (AZT) responsible for Azaspiracid Shellfish Poisoning (AZP) in northern Europe. These toxins were detected in bivalve shellfish at concentrations above regulatory limits for the first time in Norway in blue mussels in 2005 and in Sweden in blue mussels and oysters (Ostrea edulis and Crassostrea gigas) in 2018. Certain members of the diatom genus Pseudo-nitzschia produce the neurotoxin domoic acid and analogs known as Amnesic Shellfish Toxins (AST). Blooms of Pseudo-nitzschia were common in the North Sea and the Skagerrak-Kattegat, but levels of AST in bivalve shellfish were rarely above regulatory limits during the review period. Summer cyanobacteria blooms in the Baltic Sea are a concern mainly for tourism by causing massive fouling of bathing water and beaches. Some of the cyanobacteria produce toxins, e.g. Nodularia spumigena, producer of nodularin, which may be a human health problem and cause occasional dog mortalities. Coastal and shelf sea regions in northern Europe provide a key supply of seafood, socioeconomic well-being and ecosystem services. Increasing anthropogenic influence and climate change create environmental stressors causing shifts in the biogeography and intensity of HABs. Continued monitoring of HAB and phycotoxins and the operation of historical databases such as HAEDAT provide not only an ongoing status report but also provide a way to interpret causes and mechanisms of HABs.

Cytotoxic and immunological responses of fish leukocytes to nodularin exposure in vitro.

Nodularin (NOD) is a cyclic peptide released by bloom-forming toxic cyanobacteria Nodularia spumigena commonly occurring in brackish waters throughout the world. Although its hepatotoxic effects are well known, other negative effects of NOD have not yet been completely elucidated. The present study aims were to evaluate and compare the cytotoxic and immunotoxic effects of the toxin on primary leukocytes (from head kidney [HK]) and stable fish leukocytes (carp leucocyte cell line [CLC] cells). The cells were incubated with the cyanotoxin at concentrations of 0.001, 0.01, 0.05, or 0.1 µg/ml. After 24 h of exposure, the concentrations ≥0.05 µg/ml of toxin resulted in cytotoxicity in the primary cells, while in CLC cells, the toxic effect was obtained only with the highest concentration. Similarly, depending on the concentration, exposure to NOD causes a significant inhibition of chemotaxis of the phagocytic abilities of primary leukocytes and a significant reduction in the proliferation of lymphocytes isolated from the HKs. Moreover, CLC cells and HK leukocytes incubated with this toxin at all the mentioned concentrations showed an increased production of reactive oxygen and nitrogen species. NOD also evidently influenced the expression of genes of cytokine TNF-α and IL-10 and, to a minor extent, IL-1ß and TGF-ß. Notably, the observed changes in the mRNA levels of cytokines in NOD-exposed cells were evident, but not clearly dose-dependent. Interestingly, NOD did not affect the production and release of IL-1ß of the CLC cells. This study provides evidence that NOD may exert cytotoxicity and immune-toxicity effects depending on cell type and toxin concentration.

Rapid uptake and slow depuration: Health risks following cyanotoxin accumulation in mussels?

Freshwater cyanobacteria produce highly toxic secondary metabolites, which can be transported downstream by rivers and waterways into the sea. Estuarine and coastal aquaculture sites exposed to toxic cyanobacteria raise concerns that shellfish may accumulate and transfer cyanotoxins in the food web. This study aims to describe the competitive pattern of uptake and depuration of a wide range of microcystins (MC-LR, MC-LF, MC-LW, MC-LY, [Asp3]-MC-LR/[Dha7]-MC-LR, MC-HilR) and nodularins (NOD cyclic and linear) within the common blue mussel Mytilus edulis exposed to a combined culture of Microcystis aeruginosa and Nodularia spumigena into the coastal environment. Different distribution profiles of MCs/NODs in the experimental system were observed. The majority of MCs/NODs were present intracellularly which is representative of healthy cyanobacterial cultures, with MC-LR and NOD the most abundant analogues. Higher removal rate was observed for NOD (≈96%) compared to MCs (≈50%) from the water phase. Accumulation of toxins in M. edulis was fast, reaching up to 3.4 µg/g shellfish tissue four days after the end of the 3-days exposure period, with NOD (1.72 µg/g) and MC-LR (0.74 µg/g) as the dominant toxins, followed by MC-LF (0.35 µg/g) and MC-LW (0.31 µg/g). Following the end of the exposure period depuration was incomplete after 27 days (0.49 µg/g of MCs/NODs). MCs/NODs were also present in faecal material and extrapallial fluid after 24 h of exposure with MCs the main contributors to the total cyanotoxin load in faecal material and NOD in the extrapallial fluid. Maximum concentration of MCs/NODs accumulated in a typical portion of mussels (20 mussels, ≈4 g each) was beyond greater the acute, seasonal and lifetime tolerable daily intake. Even after 27 days of depuration, consuming mussels harvested during even short term harmful algae blooms in close proximity to shellfish beds might carry a high health risk, highlighting the need for testing.

Anti-inflammatory activity of glycolipids isolated from cyanobacterium Nodularia harveyana.

Activity-guided fractionations from the freshwater cyanobacterium Nodularia harveyana led to the isolation of two monogalactosyldiacylglycerols (MGDG), two digalactosyldiacylglycerols (DGDG), two monoglucosyldiacylglycerols (MGlcDG) and 1-(O-hexose)-3,25-hexacosanediol (HG). Structures were elucidated by a combination of 1D and 2D NMR analysis, HRMS and GC-MS. The potential for inhibition against TNF-α and NF-κB production of these seven compounds was tested in THP-1 cells. All compounds showed activity, but compound 7 showed higher inhibitory activity of TNF-α and NF-κB, with IC50 of 4.88 ± 0.13 and 3.64 ± 0.45 µM, respectively.

Comprehensive insights into the occurrence and toxicological issues of nodularins.

The occurrence of cyanobacterial toxins is being increasingly reported. Nodularins (NODs) are one of the cyanotoxins group mainly produced by Nodularia spumigena throughout the world. NODs may exert adverse effects on animal and human health, and NOD-R variant is the most widely investigated. However, research focused on them is still limited. In order to understand the realistic risk well, the aim of this review is to compile the available information in the scientific literature regarding NODs, including their sources, distribution, structural characteristics, physicochemical properties, biosynthesis and degradation, adverse effects in vitro and vivo, and toxicokinetics. More data is urgently needed to integrate the cumulative or synergistic effects of NODs on different species and various cells to better understand, anticipate and aggressively manage their potential toxicity after both short- and long-term exposure in ecosystem, and to minimize or prevent the adverse effects on human health, environment and the economy.

Screening and characterization of polyhydroxyalkanoate granules, and phylogenetic analysis of polyhydroxyalkanoate synthase gene PhaC in cyanobacteria.

Using Nile Red and BODIPY 493/503 dye-staining and fluorescence microscopy, twenty cyanobacterial strains, including ten commercially available strains and ten environmental isolates from estuaries, freshwater ponds, and lagoons, were screened for the accumulation of ecologically important and potentially biotechnologically significant carbon storage granules such as polyhydroxyalkanoates (PHA). Dye-staining granules were observed in six strains. Three Synechocystis, spp. strains WHSYN, LSNM, and CGF-1, and a Phormidium-like sp. CGFILA were isolated from environmental sources and found to produce granules of polyhydroxyalkanoate (PHA) according to PHA synthase gene (phaC) PCR screening and 1 H NMR analyses. The environmental isolate, Nodularia sp. Las Olas and commercially available Phormidium cf. iriguum CCALA 759 displayed granules but screened negative for PHA according to phaC PCR and 1 H NMR analyses. Partial polyhydroxyalkanoate synthase subunit C (phaC) and 16S rRNA gene sequences obtained from the PHA-accumulating strains and analyzed alongside publicly available phaC, phaE, 16S rRNA, and 23S rRNA data help in understanding the distribution and evolutionary history of PHA biosynthesis within the phylum Cyanobacteria. The data show that the presence of phaC is highly conserved within the genus Synechocystis, and present in at least one isolate of Phormidium. Maximum likelihood analyses and cophylogenetic modeling of PHA synthase gene sequences provide evidence of a recent horizontal gene transfer event between distant genera of cyanobacteria related to Pleurocapsa sp. PCC 7327 and Phormidium-like sp. CGFILA. These findings will help guide additional screening for PHA producers, and may explain why some Phormidium species produce PHAs, while others do not.

Molecular phylogenetic, population genetic and demographic studies of Nodularia douglasiae and Nodularia breviconcha based on CO1 and 16S rRNA.

Freshwater mussels belonging to the genus Nodularia (Family Unionidae) are known to be widely distributed in East Asia. Although phylogenetic and population genetic studies have been performed for these species, there still remain unresolved questions in their taxonomic status and biogeographic distribution pathways. Here, the nucleotide sequences of CO1 and 16S rRNA were newly determined from 86 N. douglasiae and 83 N. breviconcha individuals collected on the Korean Peninsula. Based on these data, we revealed the following results: (1) N. douglasiae can be divided into the three genetic clades of A (only found in Korean Peninsula), B (widely distributed in East Asia), and C (only found in the west of China and Russia), (2) the clade A is not an independent species but a concrete member of N. douglasiae given the lack of genetic differences between the clades A and B, and (3) N. breviconcha is not a subspecies of N. douglasiae but an independent species apart from N. douglasiae. In addition, we suggested the plausible scenarios of biogeographic distribution events and demographic history of Nodularia species.

Modulation of nodularin toxicity in shrimp Litopenaeus vannamei (BOONE, 1931) fed with dietary açai (Euterpe oleracea) inclusion.

This study evaluated the effect of dietary inclusion of lyophilized açaí Euterpe oleracea (LEO) on redox status of shrimp Litopenaeus vannamei (initial weight 1.5 ± 0.39 g) upon exposure to cyanotoxin nodularin (NOD) in bioflocs system. Three hundred juvenile shrimps were randomly divided into two groups and fed twice a day with two diets: one containing 0.00 (control diet) and the other 10.0% LEO (w/w) for 30-days. After the feeding period, both shrimp groups were submitted to three treatments (14 L; 7 shrimp/tank) with different concentrations of cyanotoxin NOD (0.00; 0.25; and 1.00 µg/L) dissolved in water with 96 h of exposure. Then, the shrimps were sampled (n = 15/treatment) for the determination of reduced glutathione (GSH), the activity of glutathione-S-transferase (GST), sulfhydryl groups associated to proteins (P-SH), and lipid peroxidation (TBARS) in the hepatopancreas, gills and muscle. The NOD accumulation was measured in the muscle. The results revealed that dietary LEO significantly increased GSH levels in the hepatopancreas and gills of the shrimps exposed to NOD. Toxin exposure did not modify GST activity in all organs. Muscle TBARS levels were lower in the shrimp fed with the LEO diet and exposed to NOD. The NOD toxin did not accumulate in the muscle but notably was detected in the control groups fed or not with dietary LEO. Açaí was able to induce the antioxidant system of L. vannamei, as well as lowered the oxidative damage in shrimps exposed to NOD, suggesting its use as a chemoprotectant against cyanotoxins.

Blooms of Toxic Cyanobacterium Nodularia spumigena in Norwegian Fjords During Holocene Warm Periods.

In paleoecological studies, molecular markers are being used increasingly often to reconstruct community structures, environmental conditions and ecosystem changes. In this work, nodularin, anabaenopeptins and selected DNA sequences were applied as Nodularia spumigena markers to reconstruct the history of the cyanobacterium in the Norwegian fjords. For the purpose of this study, three sediment cores collected in Oslofjorden, Trondheimsfjorden and Balsfjorden were analyzed. The lack of nodularin in most recent sediments is consistent with the fact that only one report on the sporadic occurrence and low amounts of the cyanobacterium in Norwegian Fjords in 1976 has been published. However, analyses of species-specific chemical markers in deep sediments showed that thousands of years ago, N. spumigena constituted an important component of the phytoplankton community. The content of the markers in the cores indicated that the biomass of the cyanobacterium increased during the warmer Holocene periods. The analyses of genetic markers were less conclusive; they showed the occurrence of microcystin/nodularin producing cyanobacteria of Nostocales order, but they did not allow for the identification of the organisms at a species level.

Genomic and Metabolomic Analyses of Natural Products in Nodularia spumigena Isolated from a Shrimp Culture Pond.

The bloom-forming cyanobacterium Nodularia spumigena CENA596 encodes the biosynthetic gene clusters (BGCs) of the known natural products nodularins, spumigins, anabaenopeptins/namalides, aeruginosins, mycosporin-like amino acids, and scytonemin, along with the terpenoid geosmin. Targeted metabolomics confirmed the production of these metabolic compounds, except for the alkaloid scytonemin. Genome mining of N. spumigena CENA596 and its three closely related Nodularia strains-two planktonic strains from the Baltic Sea and one benthic strain from Japanese marine sediment-revealed that the number of BGCs in planktonic strains was higher than in benthic one. Geosmin-a volatile compound with unpleasant taste and odor-was unique to the Brazilian strain CENA596. Automatic annotation of the genomes using subsystems technology revealed a related number of coding sequences and functional roles. Orthologs from the Nodularia genomes are involved in the primary and secondary metabolisms. Phylogenomic analysis of N. spumigena CENA596 based on 120 conserved protein sequences positioned this strain close to the Baltic Nodularia. Phylogeny of the 16S rRNA genes separated the Brazilian CENA596 strain from those of the Baltic Sea, despite their high sequence identities (99% identity, 100% coverage). The comparative analysis among planktic Nodularia strains showed that their genomes were considerably similar despite their geographically distant origin.

Basin-specific changes in filamentous cyanobacteria community composition across four decades in the Baltic Sea.

Almost every summer, dense blooms of filamentous cyanobacteria are formed in the Baltic Sea. These blooms may cause problems for tourism and ecosystem services, where surface accumulations and beach fouling are commonly occurring. Future changes in environmental drivers, including climate change and other anthropogenic disturbances, may further enhance these problems. By compiling monitoring data from countries adjacent to the Baltic Sea, we present spatial and temporal genus-specific distribution of diazotrophic filamentous cyanobacteria (Nostocales) during four decades (1979-2017). While the summer surface salinity decreased with a half up to one unit, the surface temperature in July-August increased with 2-3 °C in most sub-basins of the Baltic Sea, during the time period. The biovolumes of the toxic Nodularia spumigena did not change in any of the sub-basins during the period. On the other hand, the biovolume of the non-toxic Aphanizomenon sp. and the potentially toxic Dolichospermum spp. increased in the northern parts of the Baltic Sea, along with the decreased salinity and elevated temperatures, but Aphanizomenon sp. decreased in the southern parts despite decreased salinity and increased temperatures. These contradictory changes in biovolume of Aphanizomenon sp. between the northern and southern parts of the Baltic Sea may be due to basin-specific effects of the changed environmental conditions, or can be related to local adaptation by sub-populations of the genera. Overall, this comprehensive dataset presents insights to genus-specific bloom dynamics by potentially harmful diazotrophic filamentous cyanobacteria in the Baltic Sea.

Cell membrane fatty acid and pigment composition of the psychrotolerant cyanobacterium Nodularia spumigena CHS1 isolated from Hopar glacier, Pakistan.

In the present study, cyanobacterium isolate CHS1 isolated from Hopar glacier, Pakistan, was analyzed for the first time for cell membrane fatty acids and production of pigments. Sequencing of the 16-23S intergenetic region confirmed identification of the isolate CHS1 as Nodularia spumigena. All chlorophyll and carotenoid pigments were quantified using high-performance liquid chromatography and experiments to test tolerance against a range of physico-chemical conditions were conducted. Likewise, the fatty acid profile of the cell membrane CHS1 was analyzed using gas chromatography and mass spectroscopy. The cyanobacterium isolate CHS1 demonstrated tolerance to 8 g/L% NaCl, 35°C and pH 5-9. The characteristic polyunsaturated fatty acid (PUFA) of isolate CHS1, C18:4, was observed in fatty acid methyl esters (FAMEs) extracted from the cell membrane. CHS1 was capable of producing saturated fatty acids (SFA) (e.g., C16:0), monounsaturated fatty acids (MUFA) (e.g., C18:1) and polyunsaturated fatty acids (e.g., C20:5) in the cell membrane. In this study, we hypothesize that one mechanism of cold adaptation displayed by isolate CHS1 is the accumulation of high amounts of PUFA in the cell membrane.

Physiological Effects on Coexisting Microalgae of the Allelochemicals Produced by the Bloom-Forming Cyanobacteria Synechococcus sp. and Nodularia Spumigena.

Only a few studies have documented the physiological effects of allelopathy from cyanobacteria against coexisting microalgae. We investigated the allelopathic ability of the bloom-forming cyanobacteria Synechococcus sp. and Nodularia spumigena filtrates on several aspects related to the physiology of the target species: population growth, cell morphology, and several indexes of photosynthesis rate and respiration. The target species were the following: two species of green algae (Oocystis submarina, Chlorella vulgaris) and two species of diatoms (Bacillaria paxillifer, Skeletonema marinoi). These four species coexist in the natural environment with the employed strains of Synechococcus sp. and N. spumigena employed. The tests were performed with single and repeated addition of cyanobacterial cell-free filtrate. We also tested the importance of the growth phase in the strength of the allelopathic effect. The negative effects of both cyanobacteria were the strongest with repeated exudates addition, and generally, Synechococcus sp. and N. spumigena were allelopathic only in the exponential growth phase. O. submarina was not negatively affected by Synechococcus filtrates in any of the parameters studied, while C. vulgaris, B. paxillifer, and S. marinoi were affected in several ways. N. spumigena was characterized by a stronger allelopathic activity than Synechococcus sp., showing a negative effect on all target species. The highest decline in growth, as well as the most apparent cell physical damage, was observed for the diatom S. marinoi. Our findings suggest that cyanobacterial allelochemicals are associated with the cell physical damage, as well as a reduced performance in respiration and photosynthesis system in the studied microalgae which cause the inhibition of the population growth. Moreover, our study has shown that some biotic factors that increase the intensity of allelopathic effects may also alter the ratio between bloom-forming cyanobacteria and some phytoplankton species that occur in the same aquatic ecosystem.

Effects of scrubber washwater discharge on microplankton in the Baltic Sea.

In 2020, the global cap of maximum allowable sulphur content in marine fuel will be reduced from the current 3.5% to 0.5%. Another way to reduce the sulphur emissions is to install a seawater scrubber that cleans exhausts but instead release acidic water containing nutrients and contaminants back to the marine environment. In the current study, scrubber washwater was tested on a Baltic Sea microplankton community. A significant increase in chlorophyll a, particulate organic phosphorus (POP), carbon (POC) and nitrogen (PON) were observed when the community was exposed to 10% scrubber washwater for 13 days as compared to the control. A laboratory experiment with the filamentous cyanobacteria Nodularia spumigena and the chain-forming diatom Melosira cf. arctica showed negative responses in photosynthetic activity (EC10 = 8.6% for N. spumigena) and increased primary productivity (EC10 = 5.5% for M. cf. arctica), implying species-specific responses to scrubber washwater discharge.