RESUMO
An integral analysis of the acute and chronic toxicity, bioaccumulation, sites of entry, and distribution of four trace metals: copper, iron, lead, and nickel, and the non-trace metal mercury were performed in the ciliate Paramecium caudatum. Mercury was the fastest metal accumulated, and the most toxic. The sensitivity of Paramecium caudatum to the five metals tested (Cu, Fe, Hg, Ni, and Zn) falls in the range of other ciliate species. We observed similarities between the toxicity of the five metals to the ciliate P. caudatum with the rotifer Euchlanis dilatata: (a) Mercury was the most toxic metal in terms of acute and body burdens. (b) Acute values were very similar in both species, Hg as the most toxic and Fe as the less toxic, (c) the vacuole/ingestion chronic tests were more sensitive than growth inhibition chronic tests. These analyses would ideally help generate safer guidelines for protecting aquatic biota.
Assuntos
Mercúrio , Metais Pesados , Paramecium caudatum , Rotíferos , Oligoelementos , Poluentes Químicos da Água , Animais , Bioacumulação , Carga Corporal (Radioterapia) , Metais/análise , Mercúrio/análise , Oligoelementos/análise , Metais Pesados/análise , Poluentes Químicos da Água/toxicidade , Poluentes Químicos da Água/análise , Monitoramento AmbientalRESUMO
Cyanobacteria have been considered a major global threat because of their widespread ability to proliferate and contaminate inland and marine waters with toxic metabolites. For this reason, to avoid risks to humans and environmental health, regulatory legislation and guidelines have been established based on extensive toxicological data. However, most of what is known in this field come from works on microcystin (MC) variants, which effects were almost exclusively tested in metazoan models. In this work, we used acute end-point toxicological assays and high-resolution hybrid quadrupole time-of-flight mass spectrometer coupled with electrospray ionization source (ESI-Q-TOF-MS) analyses to evaluate the deleterious impact of aqueous extracts prepared from cultures of cyanobacteria and environmental bloom biomasses over a non-metazoan model organism, the cosmopolitan fresh/brackish water unicellular microeukaryote, Paramecium caudatum (Ciliophora). Our data suggest that all extracts produced time-dependent effects on P. caudatum survival, irrespective of their metabolite profile; and that this ciliate is more sensitive to extracts containing microginins than to extracts with only MCs, stressing that more toxicological investigations should be performed on the environmental impact of neglected cyanotoxins. Further, our data provide evidence that P. caudatum may be more sensitive to cyanotoxins than vertebrates, indicating that guidelines values, set on metazoans are likely to be inaccurate to protect organisms from basal food web positions. Thus, we highly recommend the widespread use of microeukaryotes, such as ciliates in environmental risk assessment frameworks for the establishment of more reliable cyanotoxin monitoring guideline values.
Assuntos
Cianobactérias/crescimento & desenvolvimento , Paramecium caudatum/fisiologia , Animais , Biomassa , Cilióforos , Cadeia Alimentar , Água Doce/microbiologia , Humanos , MicrocistinasRESUMO
Symbioses between bacteria and eukaryotes are widespread and may have significant impact on the evolutionary history of symbiotic partners. The order Rickettsiales is a lineage of intracellular Alphaproteobacteria characterized by an obligate association with a wide range of eukaryotic hosts, including several unicellular organisms, such as ciliates and amoebas. In this work, we characterized the Rickettsiales symbionts associated with two different genotypes of the freshwater ciliate Paramecium caudatum originated from freshwater environments in distant geographical areas. Phylogenetic analyses based on 16S rRNA gene showed that the two symbionts are closely related to each other (99.4% identity), belong to the family Rickettsiaceae, but are far-related with respect to previously characterized Rickettsiales. Consequently, they were assigned to a new species of a novel genus, namely "Candidatus Spectririckettsia obscura." Screening on a database of short reads from 16S rRNA gene amplicon-based profiling studies confirmed that bacterial sequences related to the new symbiont are preferentially retrieved from freshwater environments, apparently with extremely scarce occurrence (< 0.1% positive samples). The present work provides new information on the still under-explored biodiversity of Rickettsiales, in particular those associated to ciliate host cells.
Assuntos
Paramecium caudatum/microbiologia , Rickettsiales/fisiologia , Simbiose , Brasil , DNA Bacteriano/genética , Índia , Filogenia , RNA Ribossômico 16S/genética , Rickettsiales/genética , Rickettsiales/isolamento & purificaçãoRESUMO
Toxic effects of diuron and carbofuran on Paramecium caudatum were evaluated. Acute and chronic tests were conducted with diuron and carbofuran active ingredients and their commercial formulations, Diuron Nortox(®) 500 SC and Furadan(®) 350 SC, respectively. The sensitivity range of P. caudatum to reference substance sodium chloride was established. A preliminary risk assessment of diuron and carbofuran for Brazilian water bodies was performed. The tests indicated that toxicity of pure diuron and its commercial formulation was similar, while the commercial product carbofuran was more toxic than its pure form. In acute tests, readings were carried out at 2, 3, 4 and 6 h and showed an increase of mortality with increasing exposure time. The sensitivity of P. caudatum to NaCl ranged from 3.31 to 4.44 g L(-1), averaging 3.88 g L(-1). For diuron, the 6 h LC50 was 64.6 ± 3.3 mg L(-1) for its pure form and 62.4 ± 2.5 mg L(-1) for its commercial formulation. Carbofuran active ingredient was less toxic than that of diuron, presenting a 6 h LC50 of 142.0 ± 2.4 mg L(-1) for its pure form and 70.4 ± 2.2 mg L(-1) for its commercial product. Chronic tests showed that these pesticides cause significant decrease on population growth, generation number and biomass of P. caudatum. The 24 h IC50 was 7.10 ± 0.58 mg L(-1) for pure diuron, 6.78 ± 0.92 mg L(-1) for commercial diuron, 22.95 ± 3.57 mg L(-1) for pure carbofuran and 4.98 ± 0.62 mg L(-1) for commercial carbofuran. Preliminary risk assessment indicated that diuron and carbofuran present potential ecological risks for Brazilian water bodies. P. caudatum was a suitable and sensitive test organism to evaluate diuron and carbofuran toxicity to freshwater protozooplankton and, taking into account the relevant role of protozoans in aquatic environments, we strongly recommend its inclusion in ecotoxicological studies.
Assuntos
Carbofurano/toxicidade , Diurona/toxicidade , Ecotoxicologia/métodos , Monitoramento Ambiental/métodos , Paramecium caudatum/efeitos dos fármacos , Praguicidas/toxicidade , Brasil , Água Doce/química , Água Doce/microbiologiaRESUMO
Protozoans are microbial eukaryotes known to be ideal for aquatic ecotoxicological testing. Therefore, aiming to evaluate their possible use in standardized ecotoxicity assays we determined the best cultivation conditions and growth curves for two strains of the ciliated protozoan Paramecium caudatum Ehenberg 1833. One strain (PC1) was isolated from the Monjolinho reservoir-SP (22° 01 S and 47° 53 W) where the mean dissolved O2 is 5.205 mgL-1, pH 6.43 and electrical conductivity 34.75 μS cm-1. The other strain (PC2) from the Óleo lagoon in Jataí Ecological Station- SP (21° 36 S and 47° 49 W), with mean dissolved of 4,42 mgL-1, pH 4.90 and electrical conductivity 10.96 μS cm-1. The higher mean cellular biovolume and density obtained were used to evaluate different cultivation parameters such as temperature, pH, light exposition, stirring regimen and cultivation flask size. Considering protozoan densities and cell biovolume, the best culture conditions for PC1 strain was pH 9.0 at 30 °C and for PC2 was pH 7.0 at 27.5 °C. For both strains and evaluated parameters (biovolume and density), the bottle size did not interfered in the results and absence of light resulted in better ones. Concerning agitation, for PC2, there was no significant difference for this parameter and for PC1 in the absence of shaking we obtained better results. Therefore we decided to make the tests in the absence of light and without shaking. Regarding cell biovolume, the best condition was pH 9.0 at 25 ° C for the PC1 strain and pH 8.0 at 20 ° C for PC2 strain. The generation time calculated in a 96 hours growth curve was 8.35 hours for PC1 and 7.6 hours for PC2. (AU)
Assuntos
Paramecium caudatum/crescimento & desenvolvimento , Paramecium caudatum/citologiaRESUMO
Protozoans are microbial eukaryotes known to be ideal for aquatic ecotoxicological testing. Therefore, aiming to evaluate their possible use in standardized ecotoxicity assays we determined the best cultivation conditions and growth curves for two strains of the ciliated protozoan Paramecium caudatum Ehenberg 1833. One strain (PC1) was isolated from the Monjolinho reservoir-SP (22° 01 S and 47° 53 W) where the mean dissolved O2 is 5.205 mgL-1, pH 6.43 and electrical conductivity 34.75 μS cm-1. The other strain (PC2) from the Óleo lagoon in Jataí Ecological Station- SP (21° 36 S and 47° 49 W), with mean dissolved of 4,42 mgL-1, pH 4.90 and electrical conductivity 10.96 μS cm-1. The higher mean cellular biovolume and density obtained were used to evaluate different cultivation parameters such as temperature, pH, light exposition, stirring regimen and cultivation flask size. Considering protozoan densities and cell biovolume, the best culture conditions for PC1 strain was pH 9.0 at 30 °C and for PC2 was pH 7.0 at 27.5 °C. For both strains and evaluated parameters (biovolume and density), the bottle size did not interfered in the results and absence of light resulted in better ones. Concerning agitation, for PC2, there was no significant difference for this parameter and for PC1 in the absence of shaking we obtained better results. Therefore we decided to make the tests in the absence of light and without shaking. Regarding cell biovolume, the best condition was pH 9.0 at 25 ° C for the PC1 strain and pH 8.0 at 20 ° C for PC2 strain. The generation time calculated in a 96 hours growth curve was 8.35 hours for PC1 and 7.6 hours for PC2.
Assuntos
Paramecium caudatum/citologia , Paramecium caudatum/crescimento & desenvolvimentoRESUMO
The influence of Anabaena spiroides exopolysaccharides (EPS) on copper speciation (total dissolved, particulate and free Cu(2+) ions) and bioavailability in aquatic organisms was investigated. Bacteria were used as the first trophic level, Paramecium caudatum (protozoan) as the second and the copepod cyclopoid Metacyclops mendocinus as the third level. The organisms were obtained from a freshwater reservoir and held under continuous laboratory controlled conditions. Freshwater media containing EPS excreted by A. spiroides (10mgL(-1)) and copper (1.0x10(-6)molL(-1)) were used for bacteria growth. Contamined bacteria were used as food source to protozoan, which was further furnished to copepods. The results showed a reduction of EPS concentration during bacteria growth and also a smaller copper accumulation by microorganisms in the presence of EPS. We concluded that A. spiroides exopolysaccharides have reduced copper entrance into the experimental aquatic microbial food chain.
Assuntos
Anabaena/metabolismo , Cobre/análise , Cobre/metabolismo , Cadeia Alimentar , Polissacarídeos Bacterianos/química , Anabaena/crescimento & desenvolvimento , Animais , Copépodes/metabolismo , Cobre/toxicidade , Água Doce/química , Água Doce/microbiologia , Paramecium caudatum/metabolismo , Polissacarídeos Bacterianos/análise , Polissacarídeos Bacterianos/isolamento & purificaçãoRESUMO
This study aimed to investigate the influence of natural dissolved organic materials (DOM) on copper speciation (total dissolved, particulate, and free Cu2+ ions) and bioavailability during a two-level experimental microbial food chain. Bacteria were used as the first trophic level, and Paramecium caudatum (protozoan) as the second. The organisms were obtained from a freshwater reservoir and kept under controlled laboratory conditions. Three experimental treatments were performed: exposure of the organisms to copper in the absence of DOM, exposure to DOM in the absence of copper, and exposure to both copper and DOM. Freshwater medium containing natural DOM and copper at a total dissolved concentration of 1.8 x 10(-6) mol L(-1) was furnished to bacteria, which was further used as food to the protozoan. The results showed that after bacterial growth, DOM concentration decreased as quantified by total organic carbon determinations. At the same time, free Cu2+ ions concentration increased in the medium. A lower copper concentration was detected in both microorganisms in the presence of DOM. We conclude that natural DOM reduced copper accumulation in the organisms on the first and second trophic levels, thus reducing the entrance of copper into the aquatic microbial food chain.
Assuntos
Bactérias/metabolismo , Cobre/química , Cobre/metabolismo , Compostos Orgânicos/química , Paramecium caudatum/metabolismo , Animais , Calibragem , Cadeia Alimentar , Cinética , Material Particulado , Espectrofotometria AtômicaRESUMO
The binding of diatomic ligands, such as O(2), NO, and CO, to heme proteins is a process intimately related with their function. In this work, we analyzed by means of a combination of classical Molecular Dynamics (MD) and Hybrid Quantum-Classical (QM/MM) techniques the existence of multiple conformations in the distal site of heme proteins and their influence on oxygen affinity regulation. We considered two representative examples: soybean leghemoglobin (Lba) and Paramecium caudatum truncated hemoglobin (PcHb). The results presented in this work provide a molecular interpretation for the kinetic, structural, and mutational data that cannot be obtained by assuming a single distal conformation.