Effects of Soluble Cadmium Salts Versus CdSe Quantum Dots on the Growth of Planktonic Pseudomonas aeruginosa

Abstract

With their increased use, engineered nanomaterials (ENMs) will enterthe environment where they may be altered by bacteria and affect bacterial processes. Metallic ENMs, such as CdSe quantum dots (QDs), are toxic due to the release of dissolved heavy metals, but the effects of cadmium ions versus intact QDs are mostly unknown. Here, planktonic Pseudomonas aeruginosa PG201 bacteria were cultured with similar total cadmium concentrations as either fully dissolved cadmium acetate (Cd(CH3COO)2) or ligand capped CdSe QDs, and cellular morphology, growth parameters, intracellular reactive oxygen species (ROS), along with the metal and metalloid fates were measured. QDs dissolved partially in growth media, but dissolution was less in biotic cultures compared to sterile controls. Dose-dependent growth effects were similar for low concentrations of either cadmium salts or QDs, but effects differed above a concentration threshold of 50 mg/L(total cadmium basis) where (1) the growth of QD-treated cells was more impaired, (2) the membranes of QD-grown cells were damaged, and (3) QD-grown cells contained QD-sized CdSe cytoplasmic inclusions in addition to Se0 and dissolved cadmium. For most concentrations, intracellular ROS were higher for QD-versus cadmium salts-grown bacteria. Taken together, QDs were more toxic to this opportunistic pathogen than cadmium ions, and were affected by cells through QD extracellular stabilization, intracellular enrichment and cell-associated decay.

Analysis of engineered nanomaterials in complex matrices (environment and biota): General considerations and conceptual case studies

“…The co-occurrence of solutes and nanoparticles can affect nanoparticle bioavailability and uptake [12], which may inform dose and toxicity mechanism assessments. Conceptually, CdSe QDs [36] can dissolve externally to cells or can enter cells either intact after damaging membranes or accumulate in cells as highly reactive toxicants [37]. If QDs remain intact, they are subject to trophic transfer and possible biomagnification in their predators [38].…”

“…Transmission electronic microscopy instruments with energy-dispersive spectrometry (EDS), and electron diffraction can further determine the elemental composition and crystal phase, respectively. Scanning transmission electron microscopy may be particularly useful at identifying ENM in specimens at low concentrations [37], especially when used in conjunction with a high-angle annular dark field detector, which has greater sensitivity with increasing Z number for elements [39]. Electron energy loss spectroscopy can be used to obtain information about the electronic configuration of elements and is also good for quantitative analyses of low Z elements such as oxygen.…”

“…In most cases, microscope images are amenable to quantitative analysis, for example, by some analysis of feature frequency [37] or perhaps by quantitative image analysis using GIS software tools [47,48]. To enable quantitation including statistical analysis, a significant number of images acquired at random locations within a specimen are needed, as well as image acquisition from many independent replicates.…”

“…In these studies, the local electronic structure of metal centers was used to differentiate between intact metals or metal oxides and metal ions bound to receptor sites in the tissues. Similarly, studies with QDs composed of Se and Cd can trace nanoparticle integrity by interrogation of the oxidation state of Se [37]. These techniques are often less invasive than electron microscopy (EM)-based techniques; however, attention must be paid to the generation of artifacts.…”

“…1, pp. [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]2012 # 2011 SETAC Printed in the USA DOI: 10.1002/etc.723 This paper evolved from discussions held at a SETAC-endorsed Technical Workshop held at Clemson University in August, 2010. The workshop was sponsored by the United States Environmental Protection Agency (U.S. EPA), Arcadis-US, and the Clemson University Institute of Environmental Toxicology.…”