Copper status of exposed microorganisms influences susceptibility to metallic nanoparticles

Abstract

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.

Copper oxide nanoparticle toxicity profiling using untargeted metabolomics

“…Furthermore, the regulation of NFAT5 derives not only from osmotic stress, but also from growth factors, cytokines, ROS, and ions, for example [ 79 ]. The association of CuO NPs and other metal NPs (with responses attributed to ion release) with osmotic effects has already been made in the assessment of microorganisms such as algae [ 80 ] and bacteria [ 81 , 82 ], and in aquatic systems [ 83 ]. In mammalian nucleated cells, associations between metal NPs and osmotic stress-induced responses are far less reported.…”

Characteristics of the copper‐induced viable‐but‐non‐culturable state in bacteria

“…For instance, Cu-exposed cells have a lower ATP content, and a decreased electron transport and dehydrogenase activity (Chen et al 2019 ; Feng et al 2020 ). In addition, this decreased ATP content has been used to define toxic CuNP levels (Reyes et al 2016 ). While metabolic activity is by definition maintained in VBNC cells, it is often diminished.…”