Nodularia Spumigena Research Articles

How Copepods Can Eat Toxins Without Getting Sick: Gut Bacteria Help Zooplankton to Feed in Cyanobacteria Blooms.

Toxin-producing cyanobacteria can be harmful to aquatic biota, although some grazers utilize them with often beneficial effects on their growth and reproduction. It is commonly assumed that gut microbiota facilitates host adaptation to the diet; however, the evidence for adaptation mechanisms is scarce. Here, we investigated the abundance of mlrA genes in the gut of the Baltic copepods Acartia bifilosa and Eurytemora affinis during cyanobacteria bloom season (August) and outside it (February). The mlrA genes are unique to microcystin and nodularin degraders, thus indicating the capacity to break down these toxins by the microbiota. The mlrA genes were expressed in the copepod gut year-round, being >10-fold higher in the summer than in the winter populations. Moreover, they were significantly more abundant in Eurytemora than Acartia. To understand the ecological implications of this variability, we conducted feeding experiments using summer- and winter-collected copepods to examine if/how the mlrA abundance in the microbiota affect: (1) uptake of toxic Nodularia spumigena, (2) uptake of a non-toxic algal food offered in mixtures with N. spumigena, and (3) concomitant growth potential in the copepods. The findings provide empirical evidence that the occurrence of mlrA genes in the copepod microbiome facilitates nutrient uptake and growth when feeding on phytoplankton mixtures containing nodularin-producing cyanobacteria; thus, providing an adaptation mechanism to the cyanobacteria blooms.

Effects of changing phytoplankton species composition on carbon and nitrogen uptake in benthic invertebrates

AbstractPelagic primary production is the main input of organic energy for benthic production below the photic zone. In the Baltic Sea, spring phytoplankton blooms are dominated by diatoms that sink out rapidly and export nutritionally favorable matter to benthic secondary production, while the summer blooms have more variable sedimentation rates and nutritional profile. Changes in phytoplankton species composition and bloom dynamics, as a consequence of climate change and eutrophication are reducing high quality diatoms reaching the benthic fauna, while promoting cyanobacteria. Here, we test uptake and assimilation of changing phytoplankton composition for three common benthic invertebrates, a clam, an amphipod and a polychaete under varying degrees of spring‐bloom associated diatoms (Skeletonema costatum) and summer‐bloom associated cyanobacteria (Nodularia spumigena). The phytoplankton were labeled with stable isotopes (15N and 13C, respectively) in order to trace assimilation in consumers' tissues. We found that all three macrofauna species fed on both diatoms and cyanobacteria. A linear pattern was found for all three species in assimilation of carbon and nitrogen from diatoms, with increasing assimilation associated with higher proportion of diatoms. There was no clear pattern found between proportion of cyanobacteria and assimilation of carbon and nitrogen for any of the species. This study shows that the investigated macrofaunal species display a selective feeding behavior with preference for spring‐bloom associated diatoms. Thus, changes in phytoplankton bloom composition are likely affecting benthic species composition and production.

Reconstructing N<sub>2</sub>-fixing cyanobacterial blooms in the Baltic Sea beyond observations using 6- and 7-methylheptadecane in sediments as specific biomarkers

Abstract. Summer cyanobacterial blooms represent a threat to the Baltic Sea ecosystem, causing deoxygenation of the bottom water and the spread of the so-called dead zones. The history of the Baltic Sea cyanobacterial blooms is known from in situ and satellite observations since the early 1980s but is still not well understood. By comparing both weekly resolved sediment trap material and a well-dated sediment core from the eastern Gotland Basin with monitoring and satellite cyanobacterial data of the last ca. 35 years, it is shown here that 6- and 7-methylheptadecane lipids (expressed as 6+7Me-C17 : 0) may be potentially considered semiquantitative biomarkers for diazotrophic cyanobacteria, and more specifically for Nodularia spumigena. Using this organic proxy, it was thus possible to reconstruct the history of cyanobacterial blooms beyond the observational period with a resolution of 2–4 years since 1860. Cyanobacteria were constantly present but in relatively low abundance until 1920, when they started to alternate between periods with high and low abundance. Interestingly, there seems to be no significant increase in cyanobacterial abundance in the 1950s, when eutrophication and deoxygenation of the Baltic Sea increased considerably. While the early increase in cyanobacteria may be related to a small increase in phosphorus loading, decadal to multi-decadal fluctuations are likely related to variability in the Baltic Sea surface temperature and, ultimately, to the Atlantic Multi-decadal Oscillation. A 7000-year 6+7Me-C17 : 0 record from the Bothnian Sea also suggests a relationship with the mean summer temperature in the Baltic Sea region but at a multi-centennial to multi-millennial timescale. The intensity of the cyanobacterial blooms in the Baltic Sea is thus likely mainly related to natural processes such as temperature variability, at least at a multi-decadal to multi-millennial timescale.

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.

Comparative performance and emission studies of the CI engine with Nodularia Spumigena microalgae biodiesel versus different vegetable oil derived biodiesel

Biodiesel is a renewable diesel fuel that can be burned in any unmodified diesel engine at any concentration. Biodiesel from Nodularia Spumigena microalgae produced by transesterification is used in the present study. Methyl esters of algae have been prepared after successful extraction of biomass in an open pond cultivation system. Biodiesel was blended with diesel fuel with the volumetric ratios of 10% (A10) and 20% (A20). The experiments were conducted on a constant speed (1500 rpm), 4-stroke diesel engine fitted with diesel particulate filter (DPF) at a fuel injection pressure of 180 bar. Methyl esters of Karanja oil, Rice Bran oil, and Castor oil were also tested in the same engine for comparison. BSFC values increased with increase in Biodiesel blend percentage in diesel. However, K20 and A20 showed fuel economy by 5.51% and 10.06% in comparison to diesel. The emissions of CO and HC with fuel A20 are decreased by 65.77% and 53.33% respectively. The NOx emission showed an increasing trend with the blending of algae methyl esters in diesel. The presence of DPF is credited for significant reduction of PM emissions. The results predicted that the usage of algae blends could be supported, although there is a slight reduction in engine performance and an increase in NOx emissions.

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.

Computational fluid dynamic analysis of Nodularia Spumigena Microalgae Biodiesel and Karanja biodiesel blends using ANSYS in CI engine

Computational fluid dynamics is a fluid mechanics field that utilizes computational modelling and data structures. CFD simulations are being developed as a useful design tool for evaluating the dynamics of engine fluid flow and optimizing over the decades. This research explores the effect of the blending ratio on combustion properties of the CI engine and variables, such as the numerical model, the composition of fuel for simulation models and emissions in CFD analysis using the software of ANSYS FLUENT. The fuel included in the study is diesel, and, 20% mixing with Nodularia Spumigena Microalgae (A20) and Karanja biodiesel (K20) combines Combustion with Diesel. Thermal NOx emissions are comparatively lower with 13.4% and 27.4% for A20 and the K20 blend while compared to diesel. CO emissions are lower with 13.1% and 7.5% for A20 and the K20 blend when compared to diesel. Maximum temperature in the combustion zone drop about 1.76% and 2.64% is observed for K20 and the A20 blend when compared to diesel.

Phosphate and nitrate supplementations to evaluate the effect on cell biomass, intra and extracellular nodularin and nodulopeptin 901 produced by the cyanobacterium Nodularia spumigena KAC 66

Blooms of the cyanobacterium Nodularia spumigena occur regularly in the Baltic Sea typically producing a wide range of bioactive peptides including the hepatotoxin nodularin (NOD), spumigins, anabaenopeptins and nodulopeptins (molecular weights: 917, 901 and 899 Da). This study reports the production of intracellular and extracellular NOD and nodulopeptin 901 (the major secondary metabolites), at various nitrate and phosphorus concentrations produced by N. spumigena KAC 66 which had been originally isolated from the Baltic Sea. The growth was observed by cell biomass and intracellular and extracellular peptides monitored by high-performance liquid chromatography with photodiode array and mass spectrometry (HPLC-PDA-MS). In the present work, it was found that high concentrations of nitrate and phosphorus have a considerable effect on biomass and toxin levels of N. spumigena. In common with many studies, the maximum amount of NOD was retained within the cells during 5 weeks of growth. In contrast, as much as ~ 40% of nodulopeptin 901 was excreted into the medium throughout the duration of experiments. At 6.5 and 3.5 mg L−1 nitrate, the maximum concentrations of peptide per unit biomass was 1.78 ng NOD (in week 4) and 1.42 ng nodulopeptin 901 μg−1 (in week 3) were detected. However, the high concentrations of both peptides were produced in the absence of nitrate. The phosphate experiment indicated growth, and peptide production was dependent on availability of phosphorus. At 0 mg L−1 of phosphate, an increased amount of intracellular (502.4 ng μg−1 biomass) nodulopeptin 901 was recorded. This report evaluates the effect of nutrients on the production of biomass and toxins, which may predict the formation and control of blooms of N. spumigena in the Baltic Sea. It also provides information to improve the growth conditions to produce high biomass and toxins under suitable conditions, which may be helpful in the research. The results from the current study will also be helpful to predict about possible blooms of N. spumigena in the Baltic Sea with reference to increase or decrease in nitrate and phosphate concentrations.

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.

Stable and labile associations of microorganisms with the cyanobacterium Nodularia spumigena

Stable and labile associations of microorganisms with the cyanobacterium Nodularia spumigena

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 cyanobacteriumisolate 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.

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.

Effects of Salinity and Temperature on the Growth, Toxin Production, and Akinete Germination of the Cyanobacterium Nodularia spumigena

Harmful blooms of the cyanobacterium Nodularia spumigena occur in several parts of the world, and this species is notorious for its ability to produce cyanotoxins, such as nodularin. This species is also able to perform akinete differentiation, thus favoring the success of their populations under adverse conditions. In southern Brazil, N. spumigena has developed large blooms in experimental shrimp production farms. In this study, we implemented an experiment to evaluate the influence of salinity and temperature on several physiological attributes of a Brazilian strain of N. spumigena: cell growth, nodularin production, the ability to form akinetes and germination potential. A factorial experiment (3x4) was conducted to test the effects of temperature (15, 23, and 30 °C) and salinity (1, 7, 15, and 30 ppm) on the growth, production of nodularin and the differentiation of akinetes. The germination potential of the akinetes was tested after incubation for 30, 60, 90, 120, 180 and 360 days at 4 °C in the dark. N. spumigena grew under a wide range of salinity and temperatures, but salinity had a greater influence. The highest cell densities at the temperatures tested were observed at salinity 7 ppm and the lowest at salinity 1 ppm. The toxin nodularin was produced in all treatments, but there was an inverse relationship between the content of nodularin per cell and cell density. The akinetes were also differentiated in all the treatments, with the exception of S1T30. However, the largest proportion of akinetes (65% of the cells) was observed in the treatment with low cell growth at salinity 15 and 15 °C, possibly indicating an effort of the population to survive over the long term. The akinetes germinated in all treatments, but those cultivated at salinity 7 and 15 ppm (except S15T30) showed a higher percentage of germination and, in contrast, the lowest germination rate was observed in the treatments with salinity 1 ppm. Thus, the low salinity (1) at all the temperatures tested has the potential to inhibit N. spumigena blooms, since it hampers cell growth and the formation of akinetes.

Sedimentation of Nodularia spumigena and distribution of nodularin in the food web during transport of a cyanobacterial bloom from the Baltic Sea to the Kattegat

Nodularia spumigena is a toxic cyanobacteria that blooms in the Baltic Sea every year. In the brackish water of the Baltic Sea, its toxin, nodularin, mainly affects the biota in the surface water due to the natural buoyancy of this species. However, the fate of the toxin is unknown, once the cyanobacteria bloom enters the more saline waters of the Kattegat. In order to investigate this knowledge gap, a bloom of N. spumigena was followed during its passage, carried by surface currents, from the Baltic Sea into the Kattegat area, through the Öresund strait. N. spumigena cells showed an increased cell concentration through the water column during the passage of the bloom (up to 130 103 cells ml−1), and cells (4.2 103 cells ml−1) could be found down to 20 m depth, below a pycnocline. Sedimentation trap samples from below the pycnocline (10–12 m depth) also showed an increased sedimentation of N. spumigena filaments during the passage of the bloom. The toxin nodularin was detected both in water samples (0.3–6.0 μg l−1), samples of sedimenting material (a toxin accumulation rate of 20 μg m-2 day−1), zooplankton (up to 0.1 ng ind.−1 in copepods), blue mussels (70–230 μg kg−1 DW), pelagic and benthic fish (herring (1.0–3.4 μg kg−1 DW in herring muscle or liver) and flounder (1.3-6.2 μg kg−1 DW in muscle, and 11.7-26.3 μg kg−1 DW in liver). A laboratory experiment showed that N. spumigena filaments developed a decreased buoyancy at increased salinities and that they were even sinking with a rate of up to 1,7 m day−1 at the highest salinity (32 PSU). This has implications for the fate of brackish water cyanobacterial blooms, when these reach more saline waters. It can be speculated that a significant part of the blooms content of nodularin will reach benthic organisms in this situation, compared to blooms decaying in brackish water, where most of the bloom is considered to be decomposed in the surface waters.

Cyanobacterium Nodularia spumigena strain CCY9414 accumulates polyphosphate under long-term P-limiting conditions

Cyanobacterium Nodularia spumigena strain CCY9414 accumulates polyphosphate under long-term P-limiting conditions

Frequency of virus-resistant hosts determines experimental community dynamics.

Parasites, such as bacterial viruses (phages), can have large effects on host populations both at the ecological and evolutionary levels. In the case of cyanobacteria, phages can reduce primary production and infected hosts release intracellular nutrients influencing planktonic food web structure, community dynamics, and biogeochemical cycles. Cyanophages may be of great importance in aquatic food webs during large cyanobacterial blooms unless the host population becomes resistant to phage infection. The consequences on plankton community dynamics of the evolution of phage resistance in bloom forming cyanobacterial populations are still poorly studied. Here, we examined the effect of different frequencies of a phage-resistant genotype within a filamentous nitrogen-fixing Nodularia spumigena population on an experimental plankton community. Three Nodularia populations with different initial frequencies (0%, 5%, and 50%) of phage-resistant genotypes were inoculated in separate treatments with the phage 2AV2, the green alga Chlorella vulgaris, and the rotifer Brachionus plicatilis, which formed the experimental plankton community subjected to either nitrogen-limited or nitrogen-rich conditions. We found that the frequency of the phage-resistant Nodularia genotype determined experimental community dynamics. Cyanobacterial populations with a high frequency (50%) of the phage-resistant genotype dominated the cultures despite the presence of phages, retaining most of theintracellular nitrogen in the plankton community. In contrast, populations with low frequencies (0% and 5%) of the phage-resistant genotype were lysed and reduced to extinction by the phage, transferring the intracellular nitrogen held by Nodularia to Chlorella and rotifers, and allowing Chlorella to dominate the communities and rotifers to survive. This study shows that even though phages represent minuscule biomass, they can have key effects on community composition and eco-evolutionary feedbacks in plankton communities.

Limited response of a spring bloom community inoculated with filamentous cyanobacteria to elevated temperature and pCO2

Abstract Temperature and CO2 levels are projected to increase in the future, with consequences for carbon and nutrient cycling in brackish environments, such as the Baltic Sea. Moreover, filamentous cyanobacteria are predicted to be favored over other phytoplankton groups under these conditions. Under a 12-day outdoor experiment, we examined the effect on a natural phytoplankton spring bloom community of elevated temperature (from 1°C to 4°C) and elevated pCO2 (from 390 to 970 μatm). No effects of elevated pCO2 or temperature were observed on phytoplankton biovolumes, but a significantly higher photosystem II activity was observed at elevated temperature after 9 days. In addition, three species of diazotrophic filamentous cyanobacteria were inoculated to test their competitive capacity under spring bloom conditions. The toxic cyanobacterium Nodularia spumigena exhibited an average specific growth rate of 0.10 d−1 by the end of the experiment, indicating potential prevalence even during wintertime in the Baltic Sea. Generally, none of the inoculated cyanobacteria species were able to outcompete the natural phytoplankton species at temperatures ≤4°C. No direct effects were found on heterotrophic bacteria. This study demonstrates the highly efficient resistance towards short-term (12 days) changes in abiotic factors by the natural Baltic Sea spring bloom community.

Synthesis and Evaluation of Spumigin Analogues Library with Thrombin Inhibitory Activity.

Spumigins are marine natural products derived from cyanobacteria Nodularia spumigena, which mimics the structure of the d-Phe-Pro-Arg sequence and is crucial for binding to the active site of serine proteases thrombin and factor Xa. Biological evaluation of spumigins showed that spumigins with a (2S,4S)-4-methylproline central core represent potential lead compounds for the development of a new structural type of direct thrombin inhibitors. Herein, we represent synthesis and thrombin inhibitory activity of a focused library of spumigins analogues with indoline ring or l-proline as a central core. Novel compounds show additional insight into the structure and biological effects of spumigins. The most active analogue was found to be a derivative containing l-proline central core with low micromolar thrombin inhibitory activity.

Biodegradation of nodularin and other nonribosomal peptides by the Baltic bacteria

Microcystins (MCs) and nodularin (NOD), the hepatotoxic nonribosomal peptides (NRPs) produced by cyanobacteria, are considered as natural pollutants of many aquatic ecosystems. Removal of the toxins proceeds mainly through biodegradation and/or photolysis. In this study, microbial degradation of NOD and other NRPs produced by Nodularia spumigena was investigated. Both, natural bacterial consortia and individual strains from the Southern Baltic Sea were used. Bacterial samples were also screened for the presence of mlrA-D genes, previously proved to be involved in the enzymatic breakdown of hepatotoxic cyanopeptides. The Baltic sediments, with natural bacterial consortia, showed NOD-degrading activity throughout the whole year. These samples were also active against other NRPs: anabaenopeptins and spumigins. The time required for NOD biodegradation ranged from 3 to 41 days and depended on the NOD content in the collected sediments. NOD-degrading activity was also revealed in the presence of ten bacterial strains isolated from sediments and three strains isolated from filaments of N. spumigena CCNP1401. The mlrA-D genes were not found in sediments and only individual genes from the entire mlr cluster were detected in five isolated bacteria. The results suggest that in the case of Baltic bacteria other genes are involved in the biosynthesis of NOD-degrading enzymes.

Baltic Sea diazotrophic cyanobacterium is negatively affected by acidification and warming

Nitrogen fixation is a key source of nitrogen in the Baltic Sea which counteracts nitrogen loss processes in the deep anoxic basins. Laboratory and field studies have indicated that single-strain nitrogen-fixing (diazotrophic) cyanobacteria from the Baltic Sea are sensitive to ocean acidification and warming, two drivers of marked future change in the marine environment. Here, we enclosed a natural plankton community in twelve indoor mesocosms (volume ~1400 L) and manipulated pCO2 to yield six CO2 treatments with two different temperature treatments (16.6°C and 22.4°C, pCO2 range = 360 – 2030 μatm). We followed the filamentous, heterocystous diazotrophic cyanobacteria community (Nostocales, primarily Nodularia spumigena) over four weeks. Our results indicate that heterocystous diazotrophic cyanobacteria may become less competitive in natural plankton communities under ocean acidification. Elevated CO2 had a negative impact on Nodularia sp. biomass, which was exacerbated by warming. Our results imply that Nodularia sp. may contribute less to new nitrogen inputs in the Baltic Sea in future.