Abstract
The cytotoxicity of cadmium (Cd), arsenate (As(V)), and arsenite (As(III)) on a strain of Chlamydomonas acidophila, isolated from the Rio Tinto, an acidic environment containing high metal(l)oid concentrations, was analyzed. We used a broad array of methods to produce complementary information: cell viability and reactive oxygen species (ROS) generation measures, ultrastructural observations, transmission electron microscopy energy dispersive x-ray microanalysis (TEM–XEDS), and gene expression. This acidophilic microorganism was affected differently by the tested metal/metalloid: It showed high resistance to arsenic while Cd was the most toxic heavy metal, showing an LC50 = 1.94 µM. Arsenite was almost four-fold more toxic (LC50= 10.91 mM) than arsenate (LC50 = 41.63 mM). Assessment of ROS generation indicated that both arsenic oxidation states generate superoxide anions. Ultrastructural analysis of exposed cells revealed that stigma, chloroplast, nucleus, and mitochondria were the main toxicity targets. Intense vacuolization and accumulation of energy reserves (starch deposits and lipid droplets) were observed after treatments. Electron-dense intracellular nanoparticle-like formation appeared in two cellular locations: inside cytoplasmic vacuoles and entrapped into the capsule, around each cell. The chemical nature (Cd or As) of these intracellular deposits was confirmed by TEM–XEDS. Additionally, they also contained an unexpected high content in phosphorous, which might support an essential role of poly-phosphates in metal resistance.
Highlights
Freshwater ecosystems are one of the environments most seriously affected by pollution, becoming a major global threat [1,2]
Since phytoplankton species are the basis of aquatic food webs, there is a considerable body of references on the effects of heavy metals on the growth and
To gather information about these issues, in the present study, we investigate the toxic effects of Cd and As on one strain of Chlamydomonas acidophila isolated from Río Tinto (Southwest, Spain), one of the most unique examples of extreme acidic environments due to its peculiar microbial ecology, in which eukaryotic organisms are the principal contributors of biomass to the river [20]
Summary
Freshwater ecosystems are one of the environments most seriously affected by pollution, becoming a major global threat [1,2]. Heavy metals, mainly produced by industrial activity, are a primary source of contamination. They are a major cause of concern for aquatic environments due to their toxic, persistent, and accumulative properties in organisms, causing devastating effects on the ecological balance of the aquatic environment, and the diversity of aquatic animals [3]. As the metal levels increase, the concern of metal bioaccumulation through the food chain and related human health hazards rises [4]. Public Health 2020, 17, 1650; doi:10.3390/ijerph17051650 www.mdpi.com/journal/ijerph
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