John Wiley & Sons, Ltd.

Copper status of exposed microorganisms influences susceptibility to metallic nanoparticles

Although interactions of metallic nanoparticles (NP) with various microorganisms have been previously explored, few studies have examined how metal sensitivity impacts NP toxicity. Herein, we investigated the effects of copper nanoparticles' (Cu‐NPs) exposure to the model alga, Chlamydomonas reinhardtii, in the presence and absence of the essential micronutrient copper. The toxic ranges for Cu‐NPs and the ionic control, CuCl2, were determined using a high‐throughput ATP‐based fluorescence assay. Cu‐NPs caused similar mortality in copper‐replete and copper‐deplete cells (IC50: 14‐16 mg/L), but were less toxic than the ionic control, CuCl2 (IC50: 7 mg/L). Using this concentration range, we assessed Cu‐NP impacts to cell morphology, copper accumulation, chlorophyll content, and expression of stress genes under both copper supply states. Osmotic swelling, membrane damage, and chloroplast and organelle disintegration were observed by transmission electron microscopy at both conditions. Despite these similarities, copper‐deplete cells showed greater accumulation of loosely bound and tightly bound copper after exposure to Cu‐NPs. Furthermore, copper‐replete cells experienced greater loss of chlorophyll content, 19% for Cu‐NPs, compared to only an 11% net decrease in copper‐deplete cells. The tightly bound copper was bioavailable as assessed by reverse‐transcriptase quantitative PCR analysis of CYC6, a biomarker for Cu‐deficiency. The increased resistance of copper‐deplete cells to Cu‐NPs suggests that these cells potentially metabolize excess Cu‐NPs or better manage sudden influxes of ions. Our findings recommend that toxicity assessments must account for the nutritional status of impacted organisms and use toxicity models based on estimations of the bioavailable fractions. This article is protected by copyright. All rights reserved

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