title: Effects of harmful cyanobacteria on the freshwater pathogenic free-living amoeba Acanthamoeba castellanii.
abstract: Grazing is a major regulating factor in cyanobacterial population dynamics and, subsequently, considerable effort has been spent on investigating the effects of cyanotoxins on major metazoan grazers. However, protozoan grazers such as free-living amoebae can also feed efficiently on cyanobacteria, while simultaneously posing a major threat for public health as parasites of humans and potential reservoirs of opportunistic pathogens. In this study, we conducted several experiments in which the freshwater amoeba Acanthamoeba castellanii was exposed to pure microcystin-LR (MC-LR) and six cyanobacterial strains, three MC-producing strains (MC-LR, MC-RR, MC-YR, MC-WR, [Dha7] MC-RR) and three strains containing other oligopeptides such as anabaenopeptins and cyanopeptolins. Although the exposure to high concentrations of pure MC-LR yielded no effects on amoeba, all MC-producing strains inflicted high mortality rates on amoeba populations, suggesting that toxic effects must be mediated through the ingestion of toxic cells. Interestingly, an anabaenopeptin-producing strain caused the greatest inhibition of amoeba growth, indicating that toxic bioactive compounds other than MCs are of great importance for amoebae grazers. Confocal scanning microscopy revealed different alterations in amoeba cytoskeleton integrity and as such, the observed declines in amoeba densities could have indeed been caused via a cascade of cellular events primarily triggered by oligopeptides with protein-phosphatase inhibition capabilities such as MCs or anabaenopeptins. Moreover, inducible-defense mechanisms such as the egestion of toxic, MC-producing cyanobacterial cells and the increase of resting stages (encystation) in amoebae co-cultivated with all cyanobacterial strains were observed in our experiments. Consequently, cyanobacterial strains showed different susceptibilities to amoeba grazing which were possibly influenced by the potentiality of their toxic secondary metabolites. Hence, this study shows the importance of cyanobacterial toxicity against amoeba grazing and, that cyanobacteria may contain a wide range of chemical compounds capable of negatively affect free-living, herbivorous amoebae. Moreover, this is of high importance for understanding the interactions and population dynamics of such organisms in aquatic ecosystems.
authors: Departamento de Biología, Universidad Autónoma de Madrid, 28049 Madrid, Spain. Pablo.Urrutia_Cordero@biol.lu.se
authors: Pablo
authors: P
authors: Urrutia-Cordero
authors: Ramsy
authors: R
authors: Agha
authors: Samuel
authors: S
authors: Cirés
authors: María Ángeles
authors: MÁ
authors: Lezcano
authors: María
authors: M
authors: Sánchez-Contreras
authors: Karl-Otto
authors: KO
authors: Waara
authors: Hans
authors: H
authors: Utkilen
authors: Antonio
authors: A
authors: Quesada
mesh_terms: D048248:Acanthamoeba castellanii / Q000254:growth & development / Q000502:physiology*; D001427:Bacterial Toxins / Q000737:chemistry*; D003599:Cytoskeleton / Q000378:metabolism; D046869:Dolichospermum flos-aquae / Q000737:chemistry*; D004781:Environmental Exposure; D004784:Environmental Monitoring; D020387:Food Chain; D052998:Microcystins / Q000737:chemistry; D046931:Microcystis / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry*; D013045:Species Specificity
chemical_list: D001427:Bacterial Toxins; D052998:Microcystins; D010456:Peptides, Cyclic