Cyanobacteria and Their Metabolites in Mono- and Polidominant Shallow Eutrophic Temperate Lakes

Monodominant (one species dominates) or polidominant (multiple species dominate) cyanobacterial blooms are pronounced in productive freshwater ecosystems and pose a potential threat to the biota due to the synthesis of toxins. Seasonal changes in cyanobacteria species and cyanometabolites composition were studied in two shallow temperate eutrophic lakes. Data on cyanobacteria biomass and diversity of dominant species in the lakes were combined with chemical and molecular analyses of fifteen potentially toxin-producing cyanobacteria species (248 isolates from the lakes). Anatoxin-a, saxitoxin, microcystins and other non-ribosomal peptides formed the diverse profiles in monodominant (Planktothrix agardhii) and polidominant (Aphanizomenon gracile, Limnothrix spp. and Planktolyngbya limnetica) lakes. However, the harmfulness of the blooms depended on the ability of the dominant species to synthesize cyanometabolites. It was confirmed that P. agardhii produced a greater amount and diverse range of MCs and other NRPs. In the polidominant lake, isolates of the co-dominant A. gracile, L. planctonica and P. limnetica synthesized no or only small amounts of cyanometabolites. In general, the profile of cyanometabolites was greater in cyanobacteria isolates than in environmental samples, indicating a high potential for toxic cyanobacteria bloom

The predation paradox: Synergistic and antagonistic interactions between grazing by crustacean predator and infection by cyanophages promotes bloom formation in filamentous cyanobacteria

In this study, we assessed the impact of synergistic/antagonistic interactions between grazing by crustacean predator (Daphnia magna) and infection by cyanophage (Vb-AphaS-CL131) on the population dynamics of the harmful bloom-forming filamentous cyanobacterium Aphanizomenon flos-aquae. We observed synergistic effect of cyanophage infection on D. magna survival and grazing trough the lysis-induced shift in cyanobacteria population structure toward the shorter filaments. However, lysis-mediated- and grazing-enhanced removal of short A. flos-aquae filaments resulted in the dominance of grazing- and infection-resistant A. flos-aquae population. In addition, the presence of D. magna generated a trait-mediated response in the A. flos-aquae population by promoting the aggregation of filaments into colony-like structures. Experiments using temperate A. flos-aquae colony isolates from natural environment demonstrated that colony-embedded A. flos-aquae filaments are insensitive to the addition of both D. magna and cyanophages. Therefore, we propose that interactions between crustacean grazers and cyanophages may promote the emergence of defensive A. flos-aquae genotypes and population traits that eventually lead to bloom formation in aquatic environments

Morphology and distribution of phage-like particles in a eutrophic boreal lagoon* Virus-like particles Electron microscopy Curonian Lagoon

Abstract In this paper we present the results of direct observations of the morphology and size of phage-like particles by means of transmission electron microscopy (TEM) as a function of their spatial distribution in the shallow highly productive Curonian Lagoon of the Baltic Sea. In total, 26 morphologically different forms of phagelike particles were found. Different trends of distribution in terms of abundance, size and shape of virus-like particles were demonstrated. The total abundance of viruses varied from 1.91×10 7 ml −1 to 5.06×10 7 ml −1 . The virus to bacteria ratio (VBR) changed from 15.6 to 49 and was negatively associated with total bacterial numbers (r = −0.60; p < 0.05). The phages of family Myoviridae were the most diverse and were dominant at all stations

Morphology and distribution of phage-like particles in a eutrophic boreal lagoon

In this paper we present the results of direct observations of the morphology and size of phage-like particles by means of transmission electron microscopy (TEM) as a function of their spatial distribution in the shallow highly productive Curonian Lagoon of the Baltic Sea. In total, 26 morphologically different forms of phage-like particles were found. Different trends of distribution in terms of abundance, size and shape of virus-like particles were demonstrated. The total abundance of viruses varied from 1.91×107 ml-1 to 5.06×107 ml-1. The virus to bacteria ratio (VBR) changed from 15.6 to 49 and was negatively associated with total bacterial numbers (r = -0.60; p < 0.05). The phages of family Myoviridae were the most diverse and were dominant at all stations

Biogeochemical alteration of the benthic environment by the zebra mussel Dreissena polymorpha (Pallas)

The aim of this study was to verify whether the biogeochemical features (e.g. concentration of nutrients, oxygen consumption, mineralization rate, Eh) of sediments changed by the zebra mussel or its shell deposits differ from those in the ambient soft bottom, and how these differences are related to the structure of benthic macroinvertebrates. In 2006 three sampling sessions were carried out in the Curonian Lagoon, SE Baltic Sea, at three pre-defined sites, corresponding to different bottom types: zebra mussel bed, zebra mussel shell deposits and bare soft sediments. Similarity analysis of biogeochemical parameters indicated that bottom sediments covered with zebra mussel shell deposits were rather distinct from the other bottom types because of the lowest total organic matter mineralization rate and highest organic carbon, total phosphorus and total nitrogen content. The parameters measured in the zebra mussel bed did not deviate conspicuously from the values observed in bare bottoms, except for the higher rate of oxygen consumption in the upper sediment layer. Unsuitable anoxic conditions on the one hand and the ‘attractive’ shelters provided by zebra mussels on the other hand may promote the epifaunal life style in the habitats formed by dense zebra mussel clumps

Exploring viral diversity in a gypsum karst lake ecosystem using targeted single-cell genomics

Little is known about the diversity and distribution of viruses infecting green sulfur bacteria (GSB) thriving in euxinic (sulfuric and anoxic) habitats, including gypsum karst lake ecosystems. In this study, we used targeted cell sorting combined with single-cell sequencing to gain insights into the gene content and genomic potential of viruses infecting sulfur-oxidizing bacteria Chlorobium clathratiforme, obtained from water samples collected during summer stratification in gypsum karst Lake Kirkilai (Lithuania). In total, 82 viral contigs were bioinformatically identified in 62 single amplified genomes (SAGs) of C. clathratiforme. The majority of viral gene and protein sequences showed little to no similarity with phage sequences in public databases, uncovering the vast diversity of previously undescribed GSB viruses. We observed a high level of lysogenization in the C. clathratiforme population, as 87% SAGs contained intact prophages. Among the thirty identified auxiliary metabolic genes (AMGs), two, thiosulfate sulfurtransferase (TST) and thioredoxin-dependent phosphoadenosine phosphosulfate (PAPS) reductase (cysH), were found to be involved in the oxidation of inorganic sulfur compounds, suggesting that viruses can influence the metabolism and cycling of this essential element. Finally, the analysis of CRISPR spacers retrieved from the consensus C. clathratiforme genome imply persistent and active virus–host interactions for several putative phages prevalent among C. clathratiforme SAGs. Overall, this study provides a glimpse into the diversity of phages associated with naturally occurring and highly abundant sulfur-oxidizing bacteria

Absence of evidence for viral infection in colony-embedded cyanobacterial isolates from the Curonian Lagoon

The aim of the present study was to assess the frequency of viral infections in colony-embedded cells of the cyanobacteria Aphanizomenon flos-aquae and Microcystis aeruginosa collected from the brackish Curonian Lagoon. Natural and mitomycin C-treated A. flos-aquae and M. aeruginosa samples were examined for the presence of viruses and lysis by a combination of light-, epifluorescence and transmission electron microscopy techniques. Here we report a lack of evidence for virus infection, progeny formation and cell lysis in colony-embedded cells. of A. flos-aquae and M. aeruginosa. These results indicated that viruses contribute little to. the mortality of these cyanobacteria when the latter occur in colonies. Consequently, the results supported the hypothesis that colony formation can, at least temporarily, provide an efficient strategy for protection against virus-induced mortality. Finally, assuming that grazing has a negligible effect on colony-embedded cells in the Curonian Lagoon, we propose that most of the cyanobacterial biomass produced is lost from the pelagic food web by sedimentation

Draft genome sequence of the cyanobacterium Aphanizomenon flos-aquae Strain 2012/KM1/D3, isolated from the Curonian Lagoon (Baltic Sea)

We report here the de novo genome assembly of a cyanobacterium, Aphanizomenon flos-aquae strain 2012/KM1/D3, a harmful bloom-forming species in temperate aquatic ecosystems. The genome is 5.7 Mb with a G C content of 38.2%, and it is enriched mostly with genes involved in amino acid and carbohydrate metabolism

Interplay of nutrients, temperature, and competition of native and alien cyanobacteria species growth and cyanotoxin production in temperate lakes

Global warming and eutrophication contribute to formation of HABs and distribution of alien cyanobacteria northward. The current study assessed how alien to Europe Sphaerospermopsis aphanizomenoides and Chrysosporum bergii will co-occur with dominant native Planktothrix agardhii and Aphanizomenon gracile species under changing conditions in temperate freshwaters. The experiments were carried out to examine the effect of nutrients and temperature on the growth rate of cyanobacteria, production of cyanotoxins, and interspecies competition. The highest growth rate was determined for A. gracile (0.43 day-1) and S. aphanizomenoides (0.40 day-1) strains at all the tested nutrient concentrations (IP and IN were significant factors). S. aphanizomenoides adapted to the wide range of nutrient concentrations and temperature due to high species ecological plasticity; however, A. gracile was able to suppress its dominance under changing conditions. Regularity between tested variables and STX concentration in A. gracile was not found, but IP concentration negatively correlated with the amount of dmMC-RR and other non-ribosomal peptides (NRPs) in P. agardhii strains. The relative concentration of NRPs in nontoxic P. agardhii strain was up to 3-fold higher than in MC-producing strain. Our study indicated that nutrients, temperature, and species had significant effects on interspecies competition. A. gracile had a negative effect on biomass of both alien species and P. agardhii

Baltic Sea water tritium and stable isotopes in 2016–2017*

Water samples from the different basins of the Baltic Sea and North Sea were collected during four cruises taken place in 2016–2017. Altogether 60 water samples for 3H activity concentration and 120 water samples for stable isotopes ratio (δ18O and δ2H) were analysed. Exceptionally strong inflow activity from North Sea to the Baltic Sea occurred prior our surveys. The data obtained enabled comprehensive evaluation of tritium and stable isotopes distribution in waters of Baltic Sea and contributing inputs, including riverine and atmospheric freshwater flux and saline water inflow through the Danish Straits. By comparing with the previous studies, we noticed a tendency toward an increase in the δ18O and δ2H values of zero-salinity component over time, which may be due to climate change. In the case of tritium, the influence of artificial sources has also been noticed