Differences in cell wall of thin and thick filaments of cyanobacterium Aphanizomenon gracile SAG 31.79 and their implications for different resistance to Daphnia grazing

Recent studies have shown that the filamentous cyanobacterium Aphanizomenon gracile Lemmermann, strain SAG 31.79, consists of two types of filaments that differ in thickness. These two types are known to vary in resistance to Daphnia magna grazing: thin filaments (&lt;2.5 µm) are more vulnerable to grazing than the thick ones (&gt;2.5 µm). In this study, we investigated whether the difference in the vulnerability to grazing of thin and thick filaments is a result of different thickness of their cell walls, a filament stiffness determinant. We expected thick filaments to have thicker cell walls than the thin ones. Additionally, we analysed whether cell wall thickness correlates with filament thickness regardless of the filament type. A morphometric analysis of cell walls was performed using transmission electron micrographs of ultra-thin sections of the batch-cultured cyanobacterial material.  Our study revealed that the thin type of filaments had thinner cell walls than the thick filaments. Moreover, cell wall thickness was positively correlated with filament thickness. TEM (transmission electron microscopy) observations also revealed that the thin type of filaments was often at different stages of autocatalytic cell destruction, which was mainly manifested in the increase in cell vacuolization and degradation of the cytoplasm content. Based on our findings, we assume that previously reported higher resistance of thick filaments to Daphnia grazing results from greater stiffness and excellent physiological conditions of thick filaments. </p

Plankton hitch-hikers on naturalists’ instruments as silent intruders of aquatic ecosystems: current risks and possible prevention

Organism dispersal is nowadays highly driven by human vectors. This also refers to the aquatic organisms that can often silently spread in and invade new waters, especially when human vectors of dispersal act without brakes. Thus, it is mandatory to continuously identify human-mediated mechanisms of organism dispersal and implement proper biosecurity treatments. In this study, we demonstrate how the plankton net – one of the basic instruments in the equipment of every plankton sampling person is a good vector for plankton dispersal and invasions. We also demonstrate whether keeping the net in an ethanol solution after sampling is a proper biosecurity treatment, and what kind of treatments are implemented by people worldwide. The first simulation shows that bloom-forming cyanobacteria can easily infiltrate into the new environment thanks to the nets, and can prosper there. However, ethanol-based biosecurity treatment efficiently prevented their spread and proliferation in the new environment. The second simulation, based on wild plankton from an eutrophic lake, indicates that a plethora of phyto- and zooplankton taxa can infiltrate into the new waterbody through the net and sustain themselves there if the net is only flushed in the waterbody and left to dry after sampling (an approach that is commonly used by naturalists). Here, we also show that native plankton residents strongly shape the fate of hitch-hikers, but some of them like cyanobacteria can successfully compete with residents. Survey data alert us to the fact that the vast majority of biologists use either ineffective or questionable biosecurity treatments and only less than a tenth of samplers implement treatments based on disinfectant liquids. Our results emphasize that the lack of proper biosecurity methods implemented by the biologists facilitates the spread and invasions of plankton including also invasive species of a great nuisance to native ecosystems. Considering that naturalists usually use different instruments that might also be good vectors of plankton dispersal, it is necessary to develop proper uniform biosecurity treatments. No longer facilitating the plankton spread through hydrobiological instruments is the milestone that we, plankton samplers worldwide, should achieve together in the nearest future if we want to continue our desire to explore, understand, protect and save nature

Plankton hitch-hikers on naturalists’ instruments as silent intruders of aquatic ecosystems: current risks and possible prevention

Organism dispersal is nowadays highly driven by human vectors. This also refers to the aquatic organisms that can often silently spread in and invade new waters, especially when human vectors of dispersal act without brakes. Thus, it is mandatory to continuously identify human-mediated mechanisms of organism dispersal and implement proper biosecurity treatments. In this study, we demonstrate how the plankton net – one of the basic instruments in the equipment of every plankton sampling person is a good vector for plankton dispersal and invasions. We also demonstrate whether keeping the net in an ethanol solution after sampling is a proper biosecurity treatment, and what kind of treatments are implemented by people worldwide. The first simulation shows that bloom-forming cyanobacteria can easily infiltrate into the new environment thanks to the nets, and can prosper there. However, ethanol-based biosecurity treatment efficiently prevented their spread and proliferation in the new environment. The second simulation, based on wild plankton from an eutrophic lake, indicates that a plethora of phyto- and zooplankton taxa can infiltrate into the new waterbody through the net and sustain themselves there if the net is only flushed in the waterbody and left to dry after sampling (an approach that is commonly used by naturalists). Here, we also show that native plankton residents strongly shape the fate of hitch-hikers, but some of them like cyanobacteria can successfully compete with residents. Survey data alert us to the fact that the vast majority of biologists use either ineffective or questionable biosecurity treatments and only less than a tenth of samplers implement treatments based on disinfectant liquids. Our results emphasize that the lack of proper biosecurity methods implemented by the biologists facilitates the spread and invasions of plankton including also invasive species of a great nuisance to native ecosystems. Considering that naturalists usually use different instruments that might also be good vectors of plankton dispersal, it is necessary to develop proper uniform biosecurity treatments. No longer facilitating the plankton spread through hydrobiological instruments is the milestone that we, plankton samplers worldwide, should achieve together in the nearest future if we want to continue our desire to explore, understand, protect and save nature

Biocidal effect of (E)-anethole on the cyanobacterium Aphanizomenon gracile Lemmermann

Biocidal natural substances of botanical origin offer a promising ecofriendly option for controlling toxic cyanobacteria. Herein, we study 11 essential oils and some of their major components for their activity on Aphanizomenon gracile. On the basis of our results we support that Origanum vulgare and O. dictamnus, Ocimum basilicum, Eucalyptus meliodora, Melissa officinalis, and Pimpinella anisum exhibited the strongest activities, and the IC50/1d values of the extracts were calculated to be between 168.43 and 241.97 μg mL−1. When the major components of the biocidal essential oils were tested individually, (E)-anethole was found active, exhibiting an IC50/1d value of 71.35 μg mL−1. On the other hand, the half-life (t1/2) of (E)-anethole was calculated at 1 h. A preliminary attempt of (E)-anethole microencapsulation was conducted, in order to slowly release this biocidal agent, increasing the residual life under open air conditions and thus the biological activity. Results were promising since the microencapsulated product exhibited better activity than did the non-formulated (E)-anethole. This is a first report on the biocidal activity of EOs and (E)-anethole on A. gracile and a preliminary indication of the microencapsulated (E)-anethole potential use as a natural biocidal in fresh waters

Plankton hitch-hikers on naturalists' instruments as silent intruders of aquatic ecosystems: current risks and possible prevention

Organism dispersal is nowadays highly driven by human vectors. This also refers to the aquatic organisms that can often silently spread in and invade new waters, especially when human vectors of dispersal act without brakes. Thus, it is mandatory to continuously identify human-mediated mechanisms of organism dispersal and implement proper biosecurity treatments. In this study, we demonstrate how the plankton net - one of the basic instruments in the equipment of every plankton sampling person is a good vector for plankton dispersal and invasions. We also demonstrate whether keeping the net in an ethanol solution after sampling is a proper biosecurity treatment, and what kind of treatments are implemented by people worldwide. The first simulation shows that bloom-forming cyanobacteria can easily infiltrate into the new environment thanks to the nets, and can prosper there. However, ethanol-based biosecurity treatment efficiently prevented their spread and proliferation in the new environment. The second simulation, based on wild plankton from an eutrophic lake, indicates that a plethora of phytoand zooplankton taxa can infiltrate into the new waterbody through the net and sustain themselves there if the net is only flushed in the waterbody and left to dry after sampling (an approach that is commonly used by naturalists). Here, we also show that native plankton residents strongly shape the fate of hitchhikers, but some of them like cyanobacteria can successfully compete with residents. Survey data alert us to the fact that the vast majority of biologists use either ineffective or questionable biosecurity treatments and only less than a tenth of samplers implement treatments based on disinfectant liquids. Our results emphasize that the lack of proper biosecurity methods implemented by the biologists facilitates the spread and invasions of plankton including also invasive species of a great nuisance to native ecosystems. Considering that naturalists usually use different instruments that might also be good vectors of plankton dispersal, it is necessary to develop proper uniform biosecurity treatments. No longer facilitating the plankton spread through hydrobiological instruments is the milestone that we, plankton samplers worldwide, should achieve together in the nearest future if we want to continue our desire to explore, understand, protect and save nature

Effects of <i>Daphnia</i> exudates and sodium octyl sulphates on filament morphology and cell wall thickness of <i>Aphanizomenon gracile</i> (Nostocales), <i>Cylindrospermopsis raciborskii</i> (Nostocales) and <i>Planktothrix agardhii</i> (Oscillatoriales)

<p>Grazing is recognized as one of the selective factors shaping the morphology and physiology of cyanobacteria. A recent study has shown that the filamentous cyanobacterium <i>Aphanizomenon gracile</i> strain SAG 31.79 thickened in the presence of <i>Daphnia</i> (Cladocera) and its exudates. The aims of our study were: (1) to determine whether this type of response to <i>Daphnia</i> cues is common for other strains of <i>A. gracile</i>, and other species of filamentous cyanobacteria, (2) to test whether the response is due to nutrients recycled by <i>Daphnia</i>, or kairomone induced, and (3) whether it is related to toxin production. Prior to the experiment, cyanobacterial strains were inspected using chromatographic methods for the presence of two toxins, cylindrospermopsin (CYN) and three homologues of microcystin (MC-RR, MC-YR, MC-LR). HPLC analyses showed that all strains were free of cylindrospermopsin, whereas microcystins were detected only in one strain (<i>Planktothrix agardhii</i>). We then tested whether <i>Daphnia</i> exudates can cause thickening of cyanobacterial filaments, which would suggest the morphological changes in cyanobacterial filaments are caused by recycled nutrients. Cyanobacteria were also exposed to sodium octyl sulphate (a commercially available <i>Daphnia</i> kairomone). Transmission electron microscopy (TEM) was used to check whether <i>Daphnia</i> exudates and sodium octyl sulphate trigger thickening of cyanobacterial cell walls, which would be a defence mechanism against grazing. The TEM analysis revealed no significant effect of either <i>Daphnia</i> exudates or kairomone (sodium octyl sulphate) on the cell wall thickness of cyanobacteria. However, our study showed that <i>Daphnia</i> exudates triggered filament thickening in nostocalean cyanobacteria, while filaments of the oscillatorialean strain <i>P. agardhii</i> did not show this response. It was also demonstrated that sodium octyl sulphate alone can also cause filament thickening, which suggests that this might be a specific defence response to the presence of grazers.</p

Identification of Cyanometabolites and Toxicity Assessment of Cyanobacteria Isolates from Chosen Polish Eutrophic Waters and Polar Glaciers

Cyanobacteria have the ability to produce various types of bioactive compounds. Some of them can exert toxic effects on aquatic fauna, including daphnids, which are sensitive organisms that respond fast to toxins. Therefore, these crustaceans are useful for aquatic toxicity assessment. In this study, several dozen cyanobacterial strains isolated from different types of water bodies were analyzed for the presence of anabaenopeptins (APs), anatoxin-a (ATX-a), β-methylamino-L-alanine (BMAA), cylindrospermopsin (CYN), microcystins (MCs), nodularin (NOD), saxitoxin (STX) using immunoassay and chromatographic techniques. We also investigated the toxicity of extracts and filtrates from 40-days-old cyanobacterial cultures using biotests with D. magna and D. pulicaria. Analytical techniques revealed the presence of the cyanometabolites studied in isolates of Aphanizomenon (APs, BMAA, CYN, STX), Planktothrix (APs, MCs), Cuspidothrix (ATX-a, CYN) and Limnothrix (BMAA). Polar strains were free of examined compounds. Biotests revealed a reduction in Daphnia survival in response to some extracts and filtrates. It was also found in the case of one polar strain. However, there was no clear pattern indicating that extracts/filtrates from strains with identified toxic compounds reduced Daphnia survival more than other strains. This suggests that other yet unknown toxic compounds are at play. This study was financed by the Polish National Agency for Academic Exchange (project no. PPN/BEK/2020/1/00241), and partially by the National Science Centre in Poland (project no. UMO-2020/39/D/NZ8/02436)